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LUCID’s Land Use Change Analysis as an Approach for Investigating Biodiversity Loss and Land Degradation Project

By

Robert Mutuhi Chira

P.O. Box 30197Nairobi, Kenya

December 2003

Changes in Wildlife Habitat and Numbers in Embu and Mbeere Districts, Eastern Province, Kenya

LUCID Working Paper Series Number: 37

Address Correspondence to:LUCID Project

International Livestock Research InstituteP.O. Box 30709Nairobi, Kenya

E-mail: [email protected] Tel. +254-20-630743

Fax. +254-20-631481/ 631499

Changes in Wildlife Habitat and Numbers in Embu and Mbeere Districts, Eastern Province, Kenya

LUCID Working Paper Number 37

By

Robert Mutuhi Chira

P.O. Box 30197Nairobi, Kenya

December 2003

Address Correspondence to:LUCID Project

International Livestock Research InstituteP.O. Box 30709Nairobi, Kenya

E-mail: [email protected] Tel. +254-20-630743

Fax. +254-2-631481/ 631499

Copyright © 2003 by the: International Livestock Research Institute, andUnited Nations Environment Programme/Division of Global Environment Facility Coordination.All rights reserved.

Reproduction of LUCID Working Papers for non-commercial purposes is encouraged. Working papers may be quoted or reproduced free of charge provided the source is acknowledged and cited.

Cite working paper as follows: Author. Year. Title. Land Use Change Impacts and Dynamics (LUCID) Project Working Paper #. Nairobi, Kenya: International Livestock Research Institute.

Working papers are available on www.lucideastafrica.org or by emailing [email protected].

LUCID Working Paper 37 ii

TABLE OF CONTENTS

TABLE OF CONTENTS..............................................................................................................iiiCHAPTER 1: HISTORIC PERSPECTIVE OF THE SURVEY AREA...................................1

1.1 Introduction.............................................................................................................................11.2 Climatic conditions and vegetation types...............................................................................31.3 Geology and Topography........................................................................................................31.4 Soils.........................................................................................................................................31.5 Water Resources......................................................................................................................31.6 Human Population...................................................................................................................31.7 Agriculture and livestock........................................................................................................41.8 Wildlife conservation..............................................................................................................41.9 Mwea National Reserve – Location and legal status..............................................................51.10 Status of wildlife in the reserve.............................................................................................5

1.10.1 Elephants........................................................................................................................51.10.2 Other mammalian species...............................................................................................6Species.......................................................................................................................................7Reserve......................................................................................................................................8Outside.......................................................................................................................................8

1.11 Factors that led to wildlife declines in Mbeere District........................................................81.11.1 Human population increases...........................................................................................81.11.2 Poaching.........................................................................................................................91.11.3 Tree felling and land clearing.........................................................................................91.11.4 Fires..............................................................................................................................101.11.4 Fencing of the reserve..................................................................................................10

CHAPTER 2: VEGETATION CHARACTERIZATION, SPECIES COMPOSITION AND STRUCTURE IN MWEA NATIONAL RESERVE..................................................................11

2.1 Introduction...........................................................................................................................112.2 Methods.................................................................................................................................11

2.2.1 Vegetation Classification................................................................................................112.2.2 Woody plant species composition..................................................................................12

Total density of all species = -----------------------------------------------...........................................122.2.3 Woody species composition and abundance..................................................................132.2.4 Woody species structural composition...........................................................................13

2.3 Results...................................................................................................................................132.3.1 Vegetation classification................................................................................................132.3.2 Vegetation types species characterization......................................................................132.3.3 Common woody species composition and abundance...................................................142.3.4 Woody species density and diversity.............................................................................20

A. mellifera Bushed Woodland...................................................................................................21A. mellifera Bushed Woodland...................................................................................................21

2.3.5 Relative frequency of occurrence of 12 common woody species..................................212.4 Discussion.............................................................................................................................25

CHAPTER 3: HERBACEOUS LAYER SPECIES COMPOSITION, DENSITY AND DIVERSITY IN MWEA NATIONAL RESERVE....................................................................27

3.1 Introduction.........................................................................................................................273.2 Methods................................................................................................................................273.3 Results..................................................................................................................................28

3.3.1 Herbaceous species composition....................................................................................283.3.2 Wooded grasslands.........................................................................................................283.3.3 Acacia mellifera bushed woodland................................................................................28

LUCID Working Paper 37 iii

3.3.4 Commiphora africana bushed woodland.......................................................................303.3.5 Bushland.........................................................................................................................303.3.6 Wet season herbaceous species density and diversity indices........................................32

3.4 Discussion.............................................................................................................................35CHAPTER 4: MAMMALIAN SPECIES COUNT, HABITAT USE AND INTERACTION IN MWEA NATIONAL RESERVE...........................................................................................36

4.1 Introduction.........................................................................................................................364.2 Methods................................................................................................................................36

4.2.1 Mammalian species counts.............................................................................................364.3 Results..................................................................................................................................36

4.3.1 Seasonal herbivore densities and distribution................................................................364.3.2 Acacia mellifera bushed woodland................................................................................374.3.3 Commiphora africana bushed woodland.......................................................................384.3.4 Bushland vegetation type...............................................................................................394.3.6 Wooded grasslands.........................................................................................................414.3.7 Transition zone...............................................................................................................43

Wooded grasslands.........................................................................................................................434.3.8 Herbivore habitat preferences and distribution..............................................................434.3.9 Elephant interaction with other mammalian species......................................................43

F-value.........................................................................................................................................44Mean dung density during the dry season......................................................................................44Mean dung density during the wet season......................................................................................44

4.4 Discussion.............................................................................................................................455.0 References................................................................................................................................47

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LIST OF FIGURES

Figure 1: Embu and Mbeere Districts in the National context............................................2Figure 2: Mwea National Reserve – Regional setting.........................................................6Figure 3: Changes in land-cover types in Embu-Mbeere Districts between 1987 and 20019Figure 4: Changes in land-use types in Embu-Mbeere Districts between 1987 and 2001 10Figure 5: Vegetation types in Mwea National Reserve.....................................................15Figure 9: Relative frequency of 21 common woody species in the wooded grasslands in

Mwea National Reserve....................................................................................19Figure 10: Mean total Density of all species in various vegetation types in the reserve...20Figure 11: Proportion of twelve woody plant height classes in vegetation types in the

reserve ...............................................................................................................22Figure 12: Population structure denoted by relative frequency of woody species height

classes in the reserve.........................................................................................23Figure 13: Population structure denoted by relative frequency of woody speices height

classes in four vegetation types in the reserve...................................................24Figure 14: Wet season grasses and dicots dry biomass in burned and unburned wooded

grasslands..........................................................................................................30Figure 15: Wet season grasses to dicots dry bimass in three vegetation types in the

reserve................................................................................................................32Figure 16: Dung density as an index of utilization of the Acacia mellifera bushed

woodland by large herbivores during the dry and wet seasons.........................37Figure 17: Dung density as an index of utilization of the Commiphora africana bushed

woodland by large herbivores during the dry and wet seasons ........................38Figure 18: Dung density as an index of utilization of the bushland habitat by large

herbivores during the dry and wet seasons........................................................40Figure 19: Dung density as an index of utilization of the riverine vegetation type by large

herbivores during the dry and wet seasons........................................................40Figure 20: Dung density as an index of utilization of the wooded grasslands by large

herbivores during the dry and wet seasons........................................................42 Figure 21: Dung density as an index of utilization of the transition zone by large

herbivores during the dry and wet seasons........................................................42

LUCID Working Paper 37 v

LIST OF TABLES Table 1: Predation and crop destruction cases reported on average for various species in

Embu and Mbeere districts between 1979 and 1986..............................................7Table 2: Number of individuals by species encountered in Mwea National Reserve during

the 1983 and 1984 ground counts...........................................................................7Table 3: Location, fate and status of mammalian species translocated into Mwea National

Reserve....................................................................................................................8Table 4: Critical t-test values for Shannon-Wiener diversity indices between vegetation

types in Mwea National Reserve..........................................................................21Table 5: Relative frequency of 12 woody species by vegetation types in the reserve.......21Table 6: Wet season grass and dicot species composition, biomass and frequency in

burned and unburned wooded grasslands. G – Grass species; D - Dicots............28Table 7: Wet season grass and dicot species composition, biomass and frequency in three

vegetation type. G – Grass species D - Dicots......................................................31Table 8: Wet season grass species density estimates for vegetation types in the reserve. 33Table 9: Wet season dicots density estimates for vegetation types in the reserve.............34Table 10. Wet season Shannon-Wiener diversity indices and their critical t-test values

between vegetation types......................................................................................35Table 11: Dry and wet seasons mean ±SE dung density for herbivores in the A. mellifera

and the C. africana bushed woodlands.................................................................39Table 12: Dry and wet seasons mean ±SE dung density for herbivores in the bushlan and

the riverine vegetation types.................................................................................41Table 13: Dry and wet seasons mean ±SE dung density for herbivores in the transiton...43Table 14: Dry and wet seasons meanSE dung density as a measure of herbivore

occupancy for various vegetation types in Mwea NR..........................................44Table 15: G-test critical values in elephant habitat interaction with other mammalian

species in the reserve (3df)...................................................................................45

LUCID Working Paper 37 vi

CHAPTER 1: HISTORIC PERSPECTIVE OF THE SURVEY AREA

1.1 Introduction1

The survey area covers the current Embu and Mbeere Districts of Eastern Province of Kenya (Figure 1). One-third of the survey area enjoys a combination of good climate and fertile soils ideal for small scale farming (Embu District), while two-thirds mostly in Mbeere District is of marginal agricultural potential only (Jaetzold and Schmidt, 1983). The upper midland (enjoying good climate and fertile soils) had 30% of the land under annual crops, 20% of it used for perennial crops, and 20% used for grazing, while forage was produced on 6% of the farm area by 1983 (Jaetzold and Schmidt, 1983). In comparison half of land in Mbeere District was under annual crops and the other half under pasture. This reflects the different potentials of these zones.

Wildlife in most of the Embu District was decimated on the advent of commercial agricultural activities and is currently restricted in Mt. Kenya National Park and the surrounding forest. For instance by 1909, elephants were abundant in Mt. Kenya where they lived permanently. They were, however, found to move to the bamboo forest in dry period and when it was wet, they moved onto the lower slopes and raided the farms bordering the forest (Roosevelt, 1909). Roosevelt (1909) also reported entire seasonal migrations of elephants although the movements were not regular. By 1924, however, the sighting of elephants in the open country was becoming less common and elephants had become adapted forest life seeking refuge from man (Percival, 1924). By 1950s elephant crop raiding had become a long-standing problem warranting the building of moats to protect farms and shooting on control. Similar trends were observed for other wildlife species depending on level of conflict with human activities. However, there were fewer conflicts between human and wildlife within the marginal arid areas of Mbeere District. The human population was low in the Mbeere and Machakos Districts. The people in these two Districts were mainly hunter-gatherers and livestock herders. The two activities presented minimal human-wildlife conflicts and as a result wildlife was still abundant in the area up to 1970s.

Most of the marginal agricultural potential areas, in much of the now Mbeere District was not inhabited before 1914 and wildlife roamed the area with several wildlife species common to this eco-climatic zone well represented (Van de Weg and Mbuvi, 1975). The wildlife kept on decreasing with increasing human populations. For instance, the area with shallow and very shallow soils, rolling topography and dense bush north and south of the Kindaruma Dam along the Tana River was considered of no agricultural value, and was only considered suitable for range activities (Van de Weg and Mbuvi, 1975). Van de Weg and Mbuvi (1975) recommended this poorly productive land to be set aside as a game reserve. Other areas for instance Masiga block, Mavuria and Riakanau were recommended for extensive range management. The Gategi area was recommended for extensive rainfed arable farming with intermediate technology and/or large-scale rainfed arable farming to large-scale irrigation farming. The northern portion of Gategi and Kirima was recommended for small holder rainfed arable farming with intermediate technology and/or extensive range management (Van de Weg and Mbuvi, 1975).

The Mbeere District has undergone drastic human population transformation since the 1960. The district retained much of its wildlife up to 1970s until human pressure through poaching, subsistence hunting and habitat destruction drastically continued reducing their numbers. Most human pressure was emanating from increasing agricultural activities due to more human settlements by migrating communities who were primarily from the higher altitude area where they practiced agriculture.

1 This paper is derived from a Ph.D. thesis by the author from the University of Nairobi Department of Zoology.

LUCID Working Paper 37 1

Figure 1. Embu and Mbeere Districts in the National context

In comparison the Embu district had lost its wildlife earlier in the century due to escalating crop raiding conflicts resulting to erection of barriers, construction of moats and shooting on control.

This document will mainly concentrate on wildlife trends in the marginal drier areas of Mbeere district where wildlife was still abundant by 1970s although scanty literature limited quantification of wildlife numbers. The document is structured to give the climatic conditions of the area, topography, soils, historic perspective of wildlife trend, human population trends and conservation initiatives. Similarly, the report also analysis the changing anthropogenic activities that may have contributed to declines and demise of some wildlife species in the district. The report also gives a case study of the Mwea National Reserve to reflect on the past environmental conditions that prevailed within the marginal areas of Mbeere District. The climatic conditions in the district can broadly support woodlands, bushland and wooded grasslands (Pratt and Gywnne, 1977). The three vegetation types characterize the Mwea National Reserve and are used in this report in trying to reflect on the broader vegetation types that were typical of the district. The reserve is the only conservation area within the district with a sizable population of wildlife that used to roam this area. There are quite a number of wildlife species, which are now locally extinct and have the reserve as the only available opportunity for their re-introduction.


1.2 Climatic conditions and vegetation types The area enjoys a hot dry climatic conditions characteristic of much of the Eastern Province. The rainfall is bi-modal and is not well distributed over the year making it a marginal agricultural potential area. The rainfall peaks in April during the long rains and again in November during the short rains when most of the rainfall is received. There are three vegetation types characteristic of this eco-climatic zone. These vegetation types are the wooded grasslands, the bushland and woodlands (Pratt and Gywnne, 1977). Changes in vegetation types within a short distance are attributed to both changes in total rainfall and soils. For instance, at regional scale, change from forest through woodlands to grasslands could be a reflection of decline in total rainfall. Similarly, changes in vegetation over a short distance on the other hand is more likely to be a reflection of changes in soils, where changes may be due to geology or topography changes or from shallow soils on slopes to deep alluvial plains. Such a change may also reflect an interaction between geology and topography.

1.3 Geology and TopographyThe geology of the Mbeere District is mostly a basement system of granite and igneous rock (Bear, 1952). Most of the district is moderately dissected (undulating) peneplain with some portions in the western part being slightly dissected (very gently undulating) peneplain (Van de Weg and Mbuvi, 1975).

1.4 SoilsSoils in Mbeere District are developed on undifferentiated basement system rocks, well drained, shallow, dark red to yellow red stony loamy to clay (Chromic Cambosols, Paralithic and stony phase with ferralic Arenosols, Lithic phase) (Van de Weg and Mbuvi, 1975). Black cotton soils occur in flat areas suitable for irrigated agriculture. Other soil types include grey sandy soils reddish brown soils. The soils are very dusty in the dry season and muddy in the wet season and are well drained apart from the black cotton soils. The soils are highly erodable especially in areas that are over grazed or denuded and along the existing road network.

1.5 Water ResourcesApart from Tana and Thiba Rivers, which are permanent, the rest of the rivers are seasonal, running intermittently during seasonal rainfall as floods. Much of their water runs off superficially through small valleys channeled into the two major rivers. The district also partially covers part of the five hydroelectric reservoirs, the Kamburu reservoir, constructed in 1976 by the then Tana River Development Authority (now Tana and Athi Rivers Development Authority). To the west up stream, is Gitaru reservoir while down stream is Masinga reservoir constructed in 1974 and 1982 respectively (Chebures, 1989). Tana River marks the boundary between Mbeere district to the north and Machakos district to the south.

1.6 Human PopulationMbeere District was scarcely populated by 1970s. For instance, Gachoka Division had a population of approximately 77,000. There were roughly 17,000 households in the division, with a population density of 59 people per km2 by 1979 (Jaetzold and Schmidt, 1983). Migration into the area was previously very slow, perhaps because of its low agriculture potential. Due to increasing population pressure among other things, this trend has changed and new settlements are common today. Virgin land has been cleared and marginal areas are increasingly being put under cultivation. The district is now inhabited by a number of ethnic groups, two of the major ones being Embu and Mbeere. In the south and bordering Machakos District, the Kamba are represented in great numbers and through out the district there are numerous Meru and Kikuyu communities (Falk and Larsson, 1987). Most of these people are subsistence farmers with smallholding, but the Mbeere community was formerly primarily livestock keepers. Migration of other communities into the district and changes in economic trends had far reaching effects on wildlife number and habitats size in the district. The traditional way


of life and the customary security based on ties of kinship and extended families have become eroded. These changes in traditions are partially due to increasing economic pressure (Falk and Larsson, 1987). The changing traditions that tolerated wildlife and trends in economy in the district have further exacerbated the decline in wildlife numbers and their habitats in the district.

1.7 Agriculture and livestockThe main crops grown for home consumption are maize, beans, cowpeas, pigeon peas and green grams. Cotton used to be the most important cash crop in the 1970s while sorghum and millet are grown in the southern drier areas of the district. The wide range of food crops in particular the planting of sorghum and millet in Mbeere District reflects the farmers’ desire to spread production risks (Jaetzold and Schmidt, 1983). However, risk of drought and subsequent crop failure can not be excluded completely. The land under cotton production has been decreased over the years owing to high cost of farming inputs e.g. fertilizers, pesticides and delayed payments. Currently there is little or no growing of cotton in the district with farmers concentrating mainly on subsistence crop growing (Jaetzold and Schmidt, 1983). Subsistence farming and increasing human population in the district has resulted into clearing of more land for agriculture putting more pressure and minimizing areas that used to be under wildlife. Encroachment on wildlife areas has also been accelerated by changes in economic fortunes of the communities in the district who relied on cotton as a cash crop.

In addition to crop farming, most farmers keep some cattle, goats and sheep in the district. Between 11% and 25% of the grazing livestock were sheep and goats, and between 16% and 35% of the cattle kept were male (Jaetzold and Schmidt, 1983). Land adjudication has not been completed and marginal areas are increasingly being cultivated. Makima location is an example of this, where until recently, most of the farms were situated along the Thiba and Tana Rivers, but are now spreading allover the drier areas (Falk and Larsson, 1987). Farming on government land has become relatively common and is usually organized as leasehold for unspecified period of time. This has further increased pressure on formerly remaining wildlife habitats pushing some species to local extinction. The haphazard settlement on government land has turned disastrous as far as soil conservation is concern, since farmers do not feel responsible for the long-term productivity or use of the land. Instead they are most likely to extend maximum exploitation of the land they occupy (Falk and Larsson, 1987). The decreasing soil fertility has further led to clearing of more bushland and woodland for subsistence farming encroaching on wildlife habitats. Landless squatters, although few, usually living on large scale farms and government land, or on the boundaries of Mwea National Reserve engage themselves in environmentally exploitative activities such as poaching, charcoal burning and extensive farming. These activities are incompatible with wildlife conservation leading to their decline in such affected areas.

1.8 Wildlife conservationThere exists very little information on the history of wildlife numbers and their trends in Mbeere district. The area was not inhabited before 1914 and mammalian species common to this eco-climatic region were well represented. In general wildlife numbers gradually decreased as human settlements and activities in the area increased. The tremendous human population increase in the district gave way to poaching, subsistence hunting, encroachment, overgrazing and habitat destruction through charcoal burning. These activities led to decline in wildlife numbers, curtailed their movement patterns and subsequently led to local extinction of some species. Some of the locally extinct wildlife species are the giraffe, lion, leopard, cheetah, kongoni, lesser-kudu and the black rhino. It was not until 1975 that Mwea National Reserve was established to protect some of the remnant wildlife species in the area (Chebures, 1989).


1.9 Mwea National Reserve – Location and legal statusMwea National Reserve covered an area of 68km2 and was placed under the jurisdiction and management of the then larger Embu County Council in 1975. It is the only conservation area in the district. Wildlife and peasant farmers with their livestock occupied the reserve before its gazettment and were later evacuated in 1975 and allocated 10 acre plots outside the 68km2 of the reserve (Chebures, 1989). In 1978, part of the reserve was annexed during land adjudication of the entire location, leaving the current area the reserve occupies, of 42km2. The reserve is now vested under the jurisdiction of the Mbeere County Council of Mbeere District, Eastern Province.

The reserve lies at the confluence of Thiba and Tana Rivers to the northwest and southeast of the reserve respectively. The reserve borders Kamburu reservoir to the south, the second Dam in series of the country’s five hydroelectric dams. It lies between latitudes 0o 45’ and 0o 52’ south and longitudes 37o 35’ and 37o 40’ east and at an altitude of between 950m and 1150m above sea level (asl). The reserve is easily accessible from Nairobi, 180km away via Thika-Garissa road by turning north on Kitui-Embu junction, 71km east of Thika Municipality. On this road, the reserve is accessible by turning left into a murram road at Machanga shopping center a few kilometers from Kivaa Township, another distance of 11km to Makima Trading Center. The other alternative route is through Embu Municipality, through Embu-Kamburu-Kivaa road and turning right at Machanga again, 40km from Embu (Figure 2).

1.10 Status of wildlife in the reserve

1.10.1 ElephantsElephants are known to greatly affect the structure and dynamics of vegetation, whenever they occur, and if their density is high, they could seriously damage their habitat affecting other mammalian species (Kabigumila, 1993, Ruggiero, 1993, Tchamba, 1995). The elephants as been described as a keystone species due to its unique ecology (Western, 1990) and is therefore the most important wildlife species in the reserve. Mwea National Reserve is a home to a few individuals of elephants that were enclosed by the electric fence in 1998. Although no sufficient past information is available on their population status, Chebures (1989) reported 49 elephants in the reserve while Poole et al. (1992) estimated 40 individuals. Litoroh (1994) estimated a population of 50 individuals in four distinct groups. Njumbi et al. (1995) counted 48 elephants while Sakwa et al. (1995) counted 45 elephants. This shows that the elephant population has not been increasing since the 1980s. Before intensive human settlement in the area, elephants were free ranging, moving down the Tana River to Kiambere forest and probably as far as North Kitui National Reserve and back. Although human settlement has now curtailed this free movement, it is not known how much of this elephant movement took place before the electric fence was erected in 1998. However, a few elephants were known to utilize Ndune Hills, 7km northwest of the reserve during the dry season (Litoroh, 1994). The reason for the elephants' movement to Ndune Hills is not well know but is thought to have been initiated by the presence of salt licks in the area (Chebures, 1986).

Before 1998, the elephants in Mwea were known for their farm raiding, especially during the growing season, due to the high nutritive value of food crops compared to naturally available food sources. The conflicts were escalating by day and this created a demand for conflict resolution strategies. This occurred shortly after the elephant populations in the country had suffered serious poaching in 1970s and 80s. This was among the government’s strategies in ensuring their numbers build-up again in many areas of the country. Fencing of the reserve was conducted after translocating a family group of 23 individuals to Tsavo East National Park in 1996 leaving approximately 27 individuals. The aim was to reduce the elephant density in the reserve, which was 1.18 elephants km-2 ahead of an envisaged fencing program, which was completed in 1998. Mwea National Reserve is one of the smallest elephant conservation areas in the country with an elephant density of 0.6km-2 (1998 figures)


within a small area of 42km2. An indirect elephant count using elephant dung piles after a group of 23 individuals were translocated to Tsavo East National Park yielded a minimum of 50 elephants in Mwea National Reserve (Chira, 2003).

Figure 2. Mwea National Reserve – Regional setting

1.10.2 Other mammalian speciesCensus of large game in Mwea National Reserve has not been routinely conducted and has mainly been initiated for certain management decisions. For instance, the elephant counts were conducted to estimate their numbers a head of an envisaged translocation programme. The translocation was by then considered important due to increasing cases of elephant/human conflicts in the area. The rationale was to leave a manageable number of elephants that could be supported within the enclosed 42km2 of Mwea National Reserve.

Other mammalian species were also counted prior to development of a management plan for the reserve (Chebures, 1986, 1989). Table 1 shows the predation and crop destruction cases reported on


average at Embu Research station each year from 1979 to 1986 (Mwakangaru, 1989). The reported cases covers both Embu and Mbeere Districts. Cases on livestock predation and crop raiding have a bearing on species abundance although such cases will very much depend on species foraging behaviour. The hyena had the highest reported cases on livestock predation each year, while the elephant had the highest cases of reported crop destruction. This indirect deduction on numbers may hold true since the number of reported cases e.g. for lion, kongoni, leopard seemed to decrease as we approach the late 1980 (Mwakangalu, 1989). However, two ground counts were conducted in 1983 and 1984 (Table 2), which shows the abundance of various mammalian species in Mwea National Reserve. The ground surveys were carried out twice in 1983 and later in 1984 (Chebures, 1986).

Impala, buffalo, waterbuck, coke’s hartebeest (kongoni), and lesser kudu dominated the reserve by 1983. The kongoni, the lesser kudu and the bushpig are now locally extinct in the reserve as well as the surrounding areas. In 1984, the hippo, buffalo, impala and elephant were numerous in the reserve. There were, however, no records of the lesser kudu and the bushpig while only 6 kogoni were counted in 1984. This shows a drastic decline of some medium sized species within one year. These counts should, however, be considered as estimates since the thick vegetation in Mwea National Reserve precludes direct counts since visibility is reduced to less than 10m in most areas (Chira 2003).

Table 1: Predation and crop destruction cases reported on average for various species in Embu and Mbeere districts between 1979 and 1986

SpeciesPredation: Average num. of cases per species/year

SpeciesCrop destruction: Average num. of cases per species/year

Lion* 2 Elephant 49Leopard* 8 Buffalo 27Hyena* 19 Hippo 24Crocodile 6 Monkeys 22Cheetah* 2 Kongoni* 1

Wild pig* 6Warthog 4Bushbuck 29

* - Locally extinct mammalian species in Mbeere District

Table 2: Number of individuals by species encountered in Mwea National Reserve during the 1983 and 1984 ground counts

Year EL BF JK BB BP KG WB DU HP IM LK1983 7 82 3 5 3 15 26 9 - 130 131984 27 60 - 15 - 6 15 - 70 30 -

EL – Elephant BF – Buffalo JK – Jackal BB – BushbuckBP – Bushpig* KG – Kongoni* WB – Waterbuck DU – Grey duikerHP – Hippo IM – Impala LK – Lesser kudu** - Locally extinct mammalian species in Mbeere District

The reserve has lost a number of species such as the black rhino, kongoni, lesser kudu. wildpig, lion, leopard etc common to this eco-climatic region and concerted efforts are being undertaken for their re-introduction. Kenya Wildlife Service (KWS) in 2000 re-introduced the Rothschild’s giraffe, while in 2001, 30 Burchell’s zebra were also re-introduced through the assistance of Bio-diversity


Conservation Programme (BCP) of the Community Development Trust Fund (CDTF). The translocation was aimed at re-introducing the species, decimated by poachers in the 1970s to 80s and enhance attractiveness of the reserve to boost tourism in the area. Table 3 shows the population size of these two species re-introduced into the reserve (Chira 2002). Thirty zebras were translocated to Mwea National Reserve from Naivasha where on arrival five died (Table 3). Out of 25 that remained in the reserve four are alive but outside the reserve while a similar number of zebra also escaped from the reserve and can not be accounted for. Out of the 9 giraffes translocated into the reserve in 2000, the number has since increased to 12 with three young (Chira, 2002).

Table 3: Location, fate and status of mammalian species translocated into Mwea National ReserveSpecies Translocated Alive Reserve Outside Dead Unknown YoungZebra 30 21 17 4 5 4 0Giraffe 9 12 12 0 1 0 3

1.11 Factors that led to wildlife declines in Mbeere DistrictSeveral factors may have led to drastic decline of wildlife and in some cases, to species local extinction. Some of these mammalian species used to be abundant in the area in the 1960s and before. The factors leading to mammalian declines in the area are mainly anthropogenic starting with the burgeoning human population early in the 1970s. Some of these factors are discussed below.

1.11.1 Human population increasesThe district was scarcely populated by 1960s where for instance Mwea location had a population density of 10-19km-2. Similarly, its sub-locations Gategi and Riakanau had a population of 16km-2 each (Van de Weg and Mbuvi, 1975). By 1979, Mwea location had tripled it population density to 59km-2 in approximately 20 years period (Jaetzold and Schmidt, 1983). The Mbeere communities were hunter gathers and cattle herder and had no or very little impact on wildlife and its habitats. In the later years, migration by other ethnic communities into the area predominantly occupied by Mbeere and Embu ethnic groups had become common and frequent. The main causes of these migrations were in search of land for subsistence cultivation. At the same time a few ranching schemes were established for instance the Mwea Ranching Scheme. This led to clearing of bushes and woodlands, decreasing the acreage available to wildlife. After the collapse of the schemes the ranches were subdivided for settlement driving wildlife out. A case in point is the Mwea ranching scheme where by 1989 there were a few remnant wildlife species for instance the kongoni, zebra and other plains game. None of these mammalian species are found here due to present human settlements. Currently, for instance in Makima location cultivation has extended from the riverbanks to marginal drier area. These activities have interfered with wildlife habitats to an extent where the adjacent area was declared a national reserve in 1975, to protect the remaining wildlife.

Figures 3 and 4 show land cover types and land use types in Embu-Mbeere Districts between 1987 and 2001 respectively. Figure 3 shows a general decline in land cover types in the two districts where for instance the areas under bush had declined by 27.3%, those under grasslands by 13.2% while areas under woodland had declined by 17.7% in a period of 14 years. These changes are also reflected in changes in landuse types over the same period (Figure 4). The landuse types indicate that the areas under mixed bush/crops had increased from 420.9ha to 465ha while those under grazing land had decreased from 59.6ha to 36.7ha between 1987 and 2001. Information on land use changes is corroborated by changes in land use type within the same period. For instance as agricultural activities increased in the two districts, rainfed-mixed bush/cultivation and rainfed-wheat and pasture had also increased by 10.4% and 16% between 1987 and 2001 respectively (Figure 3). The two-landuse practices were mainly concentrated within the marginal areas of the districts where wildlife was plenty during the 1960s and 70s.


1.11.2 PoachingBefore 1914, the Mbeere district was scarcely populated. The human population gradually built up giving way to poaching and other wildlife malpractice. Hunting was a traditional activity before then but as the human population increased and land became scarce, hunting went beyond the subsistence level. In the later years poaching became a norm for professional commercial hunters climaxing in the 1970s and early 80s driving the rhinos to local extinction in this area. Although commercial poaching abated by late 80s, subsistence hunting continued wiping out some medium size mammalian species. Some of the mammalian specie wiped out were the lesser kudu, the bushpig and the kongoni, which were still common in the area up to late 1980s. The carnivores were a source of conflict with livestock herders and were mainly exterminated through poisoned allows and treated meat. At present only a few herbivore species are remaining in the reserve and hardly any carnivores at all.

1.11.3 Tree felling and land clearingPopulation increase in Mbeere District resulted in a number of subsistence activities such as charcoal burning and clearing more land for agriculture. The two activities have since been increasing causing reduction to woodlands and other wildlife habitats. These environmentally exploitative activities were severe on government land where the people had no responsibility for the land’s long-term productivity. The situation was made worse after the collapse of the cotton industry, which to an extent formed the main backbone of the communities’ economy. Currently tree felling is putting more pressure around and within the conservation areas where woody resources are still abundant. This has cascade effect on wildlife species by interfering with their habitats hence reducing their numbers.

Figure 3. Changes in land-cover types in Embu-Mbeere Districts between 1987 and 2001 (source: Olson et al., LUCID Working Paper 20)


Figure 4. Changes in land-use types in Embu-Mbeere Districts between 1987 and 2001 (source: Olson et al., LUCID Working Paper 20)

1.11.4 FiresFires were used at the initial stages in bush clearing for agriculture. The fires were fairly common during the dry season when they are hot enough to kill most of the vegetation. The same method is still being used in low human density areas along the main dams along Tana River. Fires are quite effective in opening virgin area for cultivation damaging wildlife habitat. Contrary to cultivated areas, fires are becoming a limiting factor to maintenance of grasslands in Mwea National Reserve where woody species continue to invade the wooded grasslands. A fire management programme is currently required to arrest the situation to encourage the wooded grassland occupancy by the resident plains game and the translocated mammalian species.

1.11.4 Fencing of the reserveBefore intensive human settlement in the area, elephants were free ranging, moving down the Tana River to Kiambere forest and probably as far as North Kitui National Park and back. Although human settlement has now curtailed this free movement, it was not known how much of the elephant movement used to take place before the electric fence was erected enclosing the reserve. Similarly, the elephants were also known to visit Ndune hills to the northeast of the reserve probably in search of salts. Before 1998 the elephants used to raid farm and due to the ensuing conflicts a population of 27 elephants were enclosed within the reserve. Elephants are known to cause serious damage to vegetation that can have far reaching consequences to other mammalian habitat users (Barnes, 1982,


Western, 1989, Dublin, et al. 1990, Waithaka, 1994, Leuthold, 1996). The fencing of elephants present an ecological imbalance that may affect other mammalian species composition and density in the reserve further reducing the reserve’s wildlife biodiversity. This may arise through elephant alteration of the reserve’s vegetation dynamic.

CHAPTER 2: VEGETATION CHARACTERIZATION, SPECIES COMPOSITION AND STRUCTURE IN MWEA NATIONAL RESERVE

2.1 IntroductionThere has been very little intensive ecological work on vegetation structure, composition and trends in Mwea National Reserve since the area was declared a National Reserve. Chebures (1986; 1989) attempted to classify the vegetation types through inventories of species characteristic of each vegetation type. However, such inventories were specifically for the purpose of developing a management plan for the reserve. His work constitutes the initial baseline information although no quantitative data was generated for future monitoring activities to detect ecological changes and the direction such changes have taken. The scenario has been complicated by the new management interventions through fencing and therefore the need to have quantitative data to be able to track down future changes in relation to possible mammalian species succession in the reserve.

In this study woodlands were further classified in relation to the most dominant species characterizing different sections of the central area of the reserve. One section of the reserve is predominantly under Acacia mellifera and hence classified as Acacia mellifera bushed woodland while the other section of the woodland is under Commiphora africana and therefore classified as Commiphora africana bushed woodland. This further vegetation classification was used to allow determination of whether there are differences in woody species density, diversity and species associations in reference to most dominant woody species. The other vegetation types i.e. the grasslands and bushland areas have common woody species peculiar to each vegetation type that required no further sub-divisions.

The aims of the present study was to quantify the various vegetation types in Mwea National Reserve through the Point Centered Quarter (PCQ) method of vegetation sampling and analysis. The data collected through PCQ method were used to determine the woody species density, dominance, frequency and their relative values. The summation of the three relative values gives a measure of species importance value. The study also aimed at quantifying the structural composition of the woody species, a factor that can be monitored for future changes. The density and diversity of these woody species were also determined, as parameters that will serve as baseline information for future analysis on trends in density and diversity.

2.2 Methods

2.2.1 Vegetation ClassificationLand-cover map was derived from Landsat TM imagery captured in January 2001 for Mwea National Reserve. An extensive field survey was carried out the same month using a GPS receiver to collect training points. These points were used in the evaluation of consistency with which land-cover types could be correctly identified from the colours of the corresponding pixels on the Landsat. The exercise aimed at collecting mid-point GPS reading of homogenous plots in each vegetation type in the field of at least 30m2, a minimum sampling area approximately equivalent to the imagery spatial resolution. These points were used in creating classification criteria for the land-cover types and accuracy assessment. Satellite imagery interpretation and geo-referencing was done using Arcview computer programme. The programme was used to collate the field observations and data with the satellite imagery to discriminate colour patterns for vegetation types.


2.2.2 Woody plant species compositionA grid map was used to locate the sampling sites in the reserve. Representative vegetation stands characterized by homogeneity in species composition and physiognomic structures were selected for stratified sampling. In each of these sites, line transects starting points were randomly selected. Transects orientation from the starting point was determined by the nature of the topographic features of the area, with transects cutting across drainage channels. A total of 49 Point Centered Quarter (PCQ) transects, each 200m long were established in the reserve to determine woody species composition in various vegetation types. Fourteen transects were set-up in Acacia mellifera bushed woodlands, 12 transects in Commiphora africana bushed woodland and wooded grasslands while a further 11 transects were established in the bushland. The individual woody species nearest to the point in each quarter was located and its basal diameter, height and point–to-individual distance determined. Woody species with basal diameter less than 1cm were not considered for PCQ analysis. The point-to-individual distances were measured to the center of the plant (Cox, 1990).

The point-to-individual distances were first totaled for all species and all points and then averaged to give the mean point-to-individual distance. The mean point-to-individual squared gave the mean area per individual, which was the average area of surface on which one individual occurs. The density per hectare in the area sampled was obtained through the following equation (Cox, 1990).

10,000 m2 Total density of all species = -----------------------------------------------

(Mean point-to-individual distance (m))2

The basal area values for individuals for each woody species were summed and divided by the number of individuals of the species to give average dominance values for various species (Cox, 1990). Absolute and relative values for density, dominance and frequency together with importance value for each woody species were determined by the following equations (Cox, 1990).

Number of individuals of a species1) Relative density = -------------------------------------- x 100

Total individuals of all species

Relative density of a species x Total density of all species2) Density = ---------------------------------------------------------------------

100

3) Dominance = Density of species x Average dominance value for species

Dominance of a species4) Relative dominance = ------------------------------------- x 100

Total dominance for all species

Number of points at which species occurs5) Frequency = --------------------------------------------------

Total number of points sampled

Frequency value for species6) Relative frequency = -------------------------------------------- x 100

Total frequency values for all species


7) Importance Value = Relative density + Relative dominance + Relative frequency

2.2.3 Woody species composition and abundanceThe PCQ transects from each vegetation type were further analyzed for 25 woody species commonly found in the reserve. The woody species relative frequencies were determined to establish the proportion and contribution of each woody species encountered in each vegetation type.

2.2.4 Woody species structural compositionThe data were further analyzed for woody species population structure, categorized into percentage woody species within the following height classes: 1-2m, 2.1-3m, 3.1-4m, 4.1-5m, 5.1-6m and >6m. The data were used to determine the proportionate contribution of each height class to total number of individual woody plants in all height classes in each vegetation type. The absolute density (number per hectare), number of species and species diversity indices for each transect were also determined. The diversity index was determined using the Shannon-Wiener equation (Cox, 1990).

H/ = - Pi log Pi

Where H/ = density and Pi = decimal fraction of individuals belonging to the ith species. ANOVA and pair-wise comparison between vegetation types for significant differences for population structural composition and distribution between height classes and relative percentage frequency were conducted using SPSS statistical packages. Arcsine data transformations for percentage values were conducted before subjecting them to parametric tests. Diversity indices were tested for differences using t-test (Zar, 1974).

2.3 Results

2.3.1 Vegetation classificationA mosaic of vegetation types occurred in the reserve (Figure 5). The map developed shows the location of various vegetation types with poorly defined boundaries between the various vegetation types. The main vegetation types were bushland, woodland (Acacia mellifera and Commiphora africana bushed woodlands), wooded grasslands and riverine vegetation types.

2.3.2 Vegetation types species characterizationWoody species PCQ data was analyzed to determine species density, density, dominance and their relative values, but tables of results not shown in this section. This section, however, shows woody species with the highest importance value index (IVI), frequencies and densities.

Thirty-five woody species were encountered in Acacia mellifera bushed woodland. seven of these A. mellifera, Commiphora africana, Grewia bicolor, Combretum aculeatum, G. virosa, Lannea sp. and G. tembensis had the highest importance value indices (IVI). High frequency and density characterized six of these seven woody species. The seventh, Lannea sp. had relatively low frequency and density, but had the highest dominance value. In Commiphora africana bushed woodland, a total of thirty-five woody species were encountered. C. africana, Acacia mellifera, premna resinosa, Grewia bicolor, A. tortilis, G. virosa and Lannea sp. were the seven woody species with the highest importance value indices. The first four woody species were characterized by high frequency and density values.

Thirty-four woody species were recorded during the study in the bushland habitat. Five of these species, C. africana, A. mellifera, G. bicolor, A. ataxacantha and Premna resinosa had the highest importance value indices. These five species were also characterized by high frequency values while the first two had the highest dominance values compared to other woody species in the habitat. In the


wooded grassland vegetation type, 47 woody species were encountered. Among these woody species Terminalia brownii, C. africana, Ormocarpum kirkii, Acacia hockii, Combretum molle, Sterculia africana, Maytenus putterickioides and Lannea sp. had the highest importance value indices exceeding 10.00 each. The first three woody species were characterized by high frequency and density values compared to other woody species in this habitat.

2.3.3 Common woody species composition and abundanceTwenty-five woody species were found in all vegetation types. Figures 6-9 show their relative frequency and abundance in each vegetation type as identified through PCQ data analysis.

Of these, 18 were very common to A. mellifera bushed woodlands, 20 very common in C. africana bushed woodlands, 23 very common in bushland areas and 21 very common in wooded grasslands. Very common species were defined as those woody plants with the relative frequency above 1% in each vegetation type.

The woody species of A. mellifera bushed woodland (Figure 6) was dominated by a composition of A. mellifera, Commiphora africana, Grewia bicolor, Combretum aculeatum and G. virosa. The five woody species constituted 65% of all the woody species in this vegetation type. Their relative frequency followed that order with A. mellifera having the highest value of 21% and the least for G. virosa at 8%. Conversely, C. africana bushed woodland (Figure 7) had 63% of the woody species composed of C. africana, A. mellifera, Premna resinosa, G. bicolor and G. virosa with C africana showing the highest relative frequency of 24% in this vegetation type.


Figure 5. Vegetation types in Mwea National Reserve


Legend for figure 6: Acacia mellifera bushed woodland woody species abbreviations and their scientific names

Species Abbreviation Species Scientific NameAca ata Acacia ataxacanthaAca bre Acacia brevispicaAca etb Acacia etbaicaAca mel Acacia melliferaAca tor Acacia tortilisAlb ant Albizia anthelminticaBos ang Boscia angustifoliaComb acu Combretum aculeatumComb exa Combretum exalatumComi afri Commiphora africanaComi edu Commiphora eduliComi sch Commiphora schimperiCord ova Cordia monoicaGrew bic Grewia bicolorGrew tem Grewia tembensiGrew vilo Grewia virosaMay put Maytenus puttrickioidesOrm kir Ormocarpum kirkiiPre res Premna resinosaSol ren Solanum renchii


Figure 6: Relative frequency of 18 common woody species in the Acacia mellifera bushed woodland in Mwea National Reserve

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G. bicolor, A. ataxacantha, Commiphora africana, Premna resinosa and A. mellifera are the most frequently common species in that order characterized the bushland habitat (Figure 8) respectively. These species relative frequencies were approximately 10% for each of the former three woody species, while A. mellifera at 8% had the least. The five woody species constituted a relative frequency of 48% of all woody species in this vegetation type.

The wooded grasslands (Figure 9) was characterized by Terminalia brownii, C. africana, Ormocarpum kirkii, A. hockii and Combretum molle as the most frequent plant species with their relative frequency decreasing in that order. The percentage frequency of occurrence was ranging between 12% for Terminalia brownii and 7% for Combretum molle. The six woody species contributed a relative frequency of 50% of all woody species in this vegetation type.

Legend for figure 7 and 8: Commiphora africana bushed woodland and bushland woody species abbreviations and their scientific names

Species Abbreviation Species Scientific NameAca ata Acacia ataxacanthaAca bre Acacia brevispicaAca etb Acacia etbaicaAca mel Acacia melliferaAca tor Acacia tortilisAlb ant Albizia anthelminticaBos ang Boscia angustifoliaCiss amp Cissus amphyllanthaComb acu Combretum aculeatumComb exa Combretum exalatumComi afri Commiphora africanaComi edu Commiphora eduliComi sch Commiphora schimperiCord ova Cordia monoicaGrew bic Grewia bicolorGrew tem Grewia tembensisGrew vilo Grewia virosaMay put Maytenus puttrickioidesOrm kir Ormocarpum kirkiiPre res Premna resinosaSol ren Solanum renchiiSte afri Sterculia africanaTer bro Terminalia brownii


Figure 7. Relative frequency of 20 common woody species in the Commiphora africana bushed woodland in Mwea National Reserve

Figure 8.:Relative frequency of 23 common woody species in the bushland habitat in Mwea National Reserve


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Figure 9: Relative frequency of 21 common woody species in the wooded grasslands in Mwea National Reserve

Legend for figure 9: Wooded grassland woody species abbreviations and their scientific names

Species Abbreviation Species Scientific NameAca hoc Acacia hockiiAca mel Acacia melliferaAca nil Acacia niloticaAca sen Acacia senegalAca tor Acacia tortilisComb frag Combretum fragransComb mol Combretum molleComi afri Commiphora africanaDob rot Dombeya rutundifoliaGrew bic Grewia bicolorGrew tem Grewia tembensisGrew vilo Grewia virosaLan riv Lannea rivaeMay put Maytenus puttrickioidesMay sen Maytenus senegalensisOrm kir Ormocarpum kirkiiOzo ins Ozoroa insignisPre res Premna resinosaRhus nat Rhus natalensisSte afri Sterculia africanaTer bro Terminalia brownii


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2.3.4 Woody species density and diversityThe density indices were calculated for all woody species including those with basal diameter of less than 1cm that were not taken into account during the PCQ data analysis. Figure 10 shows the woody species densities for four vegetation types in Mwea National Reserve. Acacia mellifera bushed woodland had the highest density of woody plants followed closely by Commiphora africana bushed woodland, while the bushland habitat had the least density. The Tukey-B post range test found significant differences between vegetation types. There were significant differences in mean total density of all woody species (F3,45 = 7.36, p<0.05) between the four vegetation types in the reserve. The mean density of woody species in the wooded grassland at 1,205/ha was significantly lower than in the Acacia mellifera, Commiphora africana bushed woodlands and in the bushland habitat (Figure 10).

The diversity indices were also calculated for all woody species including those with basal diameter of less than 1cm. The wooded grassland had the highest woody species diversity index at 1.33 followed by the bushland at 1.31 and A. mellifera bushed woodland at 1.17. The least in diversity was Commiphora africana bushed woodland at 1.09. Two of the four vegetation types, Acacia mellifera bushed woodland and Commiphora africana bushed woodland were found to be significantly different in their species diversity from the rest of the vegetation types (Table 4). The wooded grassland and bushland habitats were, however, not significantly different in their woody species diversity.

Figure 10. Mean total Density of all species in various vegetation types in the reserve


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Table 4: Critical t-test values for Shannon-Wiener diversity indices between vegetation types in Mwea National Reserve

Vegetation types A. mellifera Bushed Woodland

C. africana Bushed Woodland.

Bushland habitat

A. mellifera Bushed WoodlandC. africana Bushed Woodland. 3.28* (1844)Bushland habitat 6.45* (1816) 9.32* (1585)Wooded grasslands 6.81* (1696) 9.52* (1474) 0.09 (1439)* - Significant critical values Degrees of freedom (df) in parenthesis

2.3.5 Relative frequency of occurrence of 12 common woody speciesElephants preferred 12 woody species as food items, which were also found to be common to all vegetation types in the reserve. These species were A. mellifera, C. africana, C. edulis, C. schimperi, Grewia bicolor, G. tembensis, G. virosa, Premna resinosa, Combretum aculaetum, A. ataxacantha, A. brevispica and A. tortilis (Table 5). The 12 woody species contributed 78% of all woody species in the Acacia mellifera bushed woodland, 85% in the Commiphora africana bushed woodland, 72% in the bushland vegetation type and 22% in the wooded grasslands (Table 5). The low percentage of the 12 woody species common to all vegetation types in wooded grasslands makes the habitat unique in its species composition. The Tukey-B post range test found significant differences in the 12 woody plants relative frequency between vegetation types (F3,44 = 6.1; P<0.05), where the mean proportion of the 12 woody plants in the wooded grasslands at 5.4% differed significantly from those of other habitat types.

Table 5: Relative frequency of 12 woody species by vegetation types in the reserve

Vegetation typeSpecies A. mellifera

bushed woodland

C. africana bushed woodland

Bushland habitat

Wooded grasslands

Acacia mellifera 20.49 12.31 7.70 1.47Commiphora africana 13.29 24.14 10.43 12.23Grewia bicolor 12.68 9.97 10.11 2.77G. tembensis 3.90 2.80 2.41 0.65G. virosa 9.51 7.17 4.82 0.00Premna resinosa 2.07 9.50 9.47 2.94Combretum aculeatum 6.46 4.67 5.46 0.16A. ataxacantha 2.56 4.52 10.43 0.00A. brevispica 2.32 2.18 3.53 0.00A. tortilis 1.34 3.43 2.25 1.47C. edulis 1.59 2.80 1.77 0.49C. schimperi 2.07 1.40 3.53 0.00Total 78% 85% 72% 22%


Figure 11 shows the proportion of height classes of the 12 woody species for each vegetation type. A higher proportion of woody species within height class 1-2m There were more of these 12 woody species in other vegetation types compared to the wooded grasslands vegetation type constituted the wooded grasslands. The rest of the vegetation types were mainly dominated by woody species below 4m in height. Woody plant species of 4m in height or below constituted 85% of all woody species in the reserve, 65% of which were the 12 most common woody species to all habitats.

Figure 11: Proportion of twelve woody plant height classes in vegetation types in the reserve

The structural composition (species distribution between height classes), however, did not differ significantly (Figure 11) between these four vegetation types (F3,20 = 0.10; P>0.05). The vegetation types in Mwea National Reserve may therefore be broadly defined by the dominance (or co-dominance) of one of the identified 12 common woody plant species.

2.3.5.1 General woody species structural compositionFigure 12 and 13 show the population structure denoted by relative frequency of woody species height classes. The results give the proportion of each height class to the total woody individuals enumerated in each vegetation type. The woody species were categorized into total individuals woody plants constituting height classes namely: 1-2m, 2.1-3m, 3.1-4m, 4.1-5m, 5.1-6m and >6m in height.

Figure 12 shows relative frequency of six height size classes of woody species in the reserve. The relative frequency denotes the population structure (woody species height class distribution) in Mwea National Reserve. The Tukey-B post range test found significant differences between the mean proportion of woody plants within height classes 1-2m and 2.1-3m high at 33.09% and 29.81%


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respectively (Figure 12), compared to all other height classes in the reserve (F5,288 = 41; P<0.05). Similarly the mean proportion of woody plants within height classes 3.1-4m at 22.8% and 4.1-5 at 19.99% were also significantly different from those of height classes 5.1-6m and >6m high respectively. The population structure was skewed in favour of smaller woody plants.

Figure 12: Population structure denoted by relative frequency of woody species height classes in the reserve

2.3.5.2 Acacia mellifera bushed woodland vegetation type The woody species distribution within each class reflects that of the whole reserve where height classes 4m in height and below constituted 72% of all woody species encountered (Figure 14). The Tukey-B post range test found significant differences between different height classes (F5,72 = 10.4; P<0.05). The mean proportion of individuals within height class 5-6m high at 14.57%, were significantly lower compared to those within height classes 1-2m, 2.1-3, 3.1-4m and those within height class 4.1-5m. Similarly, the mean proportion of individual plants within height class >6m had a lower mean of 16.04%, which differed significantly from those of height classes 1-2m, 2.1-3m and 3.1-4m high. This vegetation type was, however, dominated by woody species within height classes below 3m. The least mean proportion of woody species was within height class 5.1-6m in height (Figure 13).

2.3.5.3 Commiphora africana bushed woodland vegetation typeThe woody species height classes below 4m high constituted 69% of all woody plant species in this vegetation type, a population structure in favour of the lower height classes. The Tukey-B post range test found significant differences in the proportion of woody plants among different height classes.


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Figure 13: Population structure denoted by relative frequency of woody speices height classes in four vegetation types in the reserve

The mean proportion of individual woody plants within height class 2.1-3m at 33.15% (Figure 13) was significantly higher compared to those in all other height classes in this vegetation type (F5,66 = 14.3; P<0.05).

There was also a significant difference in the proportion of woody plants between height class 5.1-6m at 16.08% and height classes 1-2m and 3.1-4m both of which hand higher means. Similarly height class >6m had a lower mean proportion of woody plants at 11.08%, which differed significantly from those of height classes 1-2m and 3.1-4m high. The mean proportion of woody plants within height class 4.1-5m had a higher mean at 22.03%, which differed significantly with that within height class >6m in height. The highest proportion of woody species in Commiphora africana bushed woodland were found within height classes below 3m in height, while the least were among those above 6m high.

2.3.5.4 Bushland vegetation typeThe population structure in the bushland vegetation type was also skewed in favour of height classes 2.1-3m and 3.1-4m high, which constituted 55% of all woody plant found here (Figure 13). Most of


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70.0

A.mellifera bushed woodland C. africana bushed woodland Bushland habitat Wooded grassland

Vegetation type

Rel

. fre

q.1-2m 2.1-3m 3.1-4m 4.1-5m 5.1-6m >6m

the woody individuals found in this vegetation type were within height classes 2.1-3m and 3.1-4m high. This was a deviation in trend from the other vegetation types which had higher percentages of woody plant species within height classes 1-2m and 2.1-3m. However, the height categories of 3.1-4m and below in height constituted 71% of all woody plant species which compared well with other vegetation types.

The Tukey-B post range test found significant differences in the proportion of woody plants between height classes (Figure 13) in favour of lower height classes (F5,60 = 13.8; P< 0.05). The mean proportion of woody plants found within height class 2.1-3m at 32.99% was significantly higher compared to those of height classes 1-2m, 4.1-5m, 5.1-6 and mean proportion of woody plants above 6m. The mean proportion of woody plants within height class 3.1-4m at 26.88%was also significantly higher compared to those of height classes 5.1-6m and over 6m high. There was also a significantly lower mean proportion of woody plants within height class >6m at 10.09% compared to those in height classes 1-2m and 4.1-5m high.

2.3.5.5 Wooded grasslands vegetation typeThe population structure in the wooded grasslands was in favour of height class 1-2m, which constituted 65% of all woody plant species in this vegetation type (Figure 13). Approximately 91% of all woody species in this vegetation type were below 4m in height. The population structure defined by proportion of woody plants within height classes, also shows a significant difference as in the other vegetation types (F5,66 = 78; P<0.05). The mean proportion of woody plants within height class 1-2m high at 54.64% was significantly higher compared to those of other height classes (Figure 13). Similarly there were significant differences in mean proportion of woody plants in height class 2.1-3m at 24.05%, which was higher compared to all others height classes. Mean proportion of individual woody plants in height class 3.1-4m at 15.1% was significantly higher compared to those in height class >6m high.

2.4 DiscussionThe PCQ results show that Mwea National Reserve (MNR) vegetation types can be distinctively characterized by the dominance or co-dominance of one or two of the 12 identified woody species. The four main vegetation types are dominated or co-dominated by either Acacia mellifera, Commiphora africana, Grewia bicolor, G. virosa and A. ataxacantha woody species with the exception of the wooded grasslands. Terminalia brownii and C. africana among other woody species dominated the wooded grasslands making it a unique vegetation type from the others. The woody species compositional difference between the three vegetation type, namely the A. mellifera bushed woodland, C. africana bushed woodland and the bushland from the wooded grasslands can be explained mainly by differences in endaphic factors. For instance the areas covered by wooded grasslands have black cotton, gray sandy and reddish soils, while the areas covered by woodlands and the bushland have reddish to grey sandy soils (Bear, 1952). The wooded grassland had the most distinctive woody species composition from other vegetation types making it the most diverse in species composition probably owing to these endaphic factors.

The proportion of the 12 woody species in each vegetation type complement the PCQ results in that in A. mellifera and C. africana bushed woodlands they constituted 78% and 85% of all woody plants found in these habitats respectively (see Table 5). Similarly the proportion of the 12 woody species constituted 72% and 22% of all woody plants in the bushland and wooded grasslands respectively. The proportion of the 12 woody species again shows the compositional difference and abundance of woody species between the wooded grasslands and other vegetation types. The wooded grassland had the highest diversity compared to other vegetation types although it had significantly lower mean density of woody plants (F3.45 = 7.36; p<0.05). Other vegetation types did not show any differences in their woody species densities.


The population structure of woody plants in the reserve was in favour of woody plants below 3m in height. The mean percentage of woody plants below 3m in height in A. mellifera bushed woodland (59%), C. africana bushed woodland (59%) and bushland (57%) were almost similar but lower, compared to those of the wooded grasslands at 79% (Figure 13). The increase in seedlings (>1m) and immature (1-3m) woody plants in the wooded grasslands indicates invasion of this habitat by young woody species or probably lack of their utilization by elephants. Elephant visitation of the wooded grasslands was lower compared to other vegetation types. There was, however, no significant variation in the structural composition (F5,288 = 0.1; P>0.05) between vegetation types in that they were all dominated by woody plants below 3m compared to those above 3m in height. This observation is a clear indicator of a healthy plant community with high recruitment rate and lack of serious perturbation by elephants. It is evident from this study that the recruitment woody plants are cable of replacing mature woody plants drying through elephant related mortality and other causes.

The vegetation in MNR does not show evidence of high elephant pressure on seedlings and recruitment classes. Switching to these two height classes for food by elephants may have serious repercussions on vegetation in the reserve. In comparison, Dublin et al. (1990) noted that in the 1990s, there were few trees in the larger height-classes in the Serengeti-Mara ecosystem and elephants were feeding on the small seedlings. The scenario was different in the 1960s where elephants largely ignored seedlings (Croze, 1974). Norton-Griffiths (1979) and Dublin et al. (1990) further observed that although the switching from large to younger woody plants may have been a reflection of availability rather than preference, it had important repercussions. This is because woodlands seem to be far more sensitive to impact on regenerating seedlings than to those on mature trees (Norton-Griffiths (1979) and Dublin et al. 1990). Caughley’s (1976) “Stable limit cycle hypothesis” of woodland recovery requires that seedlings have a safe refuse from elephants. Destruction of young trees (<1m) is an important factor (Ross et al., 1976) and it raises concern when it reaches 50% of total woody species within this height class. Destruction and reduction of seedlings in MNR should serve as a future signal for immediate reduction of number of elephants in the reserve.

It is necessary to strike a balance between the elephant and the woodland to provide adequate relief for seedling trees. Ross et al. (1976) observes that this balance would be achieved when the number of young trees entering the mature age class is approximately equal to the number of mature trees dying while still considering other factors other than tree mortality from the effect of elephant browsing. Constant monitoring of woody plants height classes may help in determining the timing of the most appropriate management intervention to reduce habitat destruction by elephants and other causes.


CHAPTER 3: HERBACEOUS LAYER SPECIES COMPOSITION, DENSITY AND DIVERSITY IN MWEA NATIONAL RESERVE

3.1 IntroductionMwea National Reserve was not previously actively managed even though a couple of management plans were developed in 1980s. One of the major vegetation type that is faced with serious threat are the wooded grasslands. This vegetation type has a high proportion of recruitment woody plants mainly invading from the woodlands of the reserve (see chapter 2). Similarly, there are also incidences of invasive herbaceous species that have also dominated the wooded grasslands (Chira, 2002). The invasion by both the woody and herbaceous species has lowered the quality and quantity of food resources of the wooded grasslands (Chira 2002). The invasive species trends has not been arrested due to lack of a fire management plan for over 20 years according to reserve’s records. The study has demonstrated the usefulness of a fire management programme for the reserve. There were some areas, which were accidentally burned during this study, with fires originating from near human settlements. The burned areas show emergence of grass species that are stimulated by fires and are of high quality to herbivores. With the current re-introductions, there is need to maintain the quality of the reserve’s wooded grasslands.

Quantification of the reserve’s woody and herbaceous species composition and structure at this point in time was aimed at providing baseline information on the present status of the reserve’s herbaceous layer. This information is a pre-requisite in the management of the reserve and its biodiversity as well as providing the necessary platform and insight in assessing the future direction of change of ecological processes in the reserve. The study also aimed at identifying indicator woody and herbaceous plants that may be used in future assessment of the mammalian species role in the reserve. Such changes in both the woody species and the herbaceous layer may have varying impact on other mammalian species and bio-diversity in the reserve in general. The study looks at the herbaceous species composition, density and diversity in all vegetation categories of the reserve.

3.2 MethodsA total of 22 transects were established in Mwea National Reserve immediately after the wet season for herbaceous layer sampling. The data represent information on herbaceous layer biomass, density, cover and frequency after the end of the short rains. A section of wooded grassland adjacent to human settlement was accidentally burned. This section was sampled and data acquired compared with that collected for the unburned area of the wooded grasslands. Twelve transects were randomly established in the wooded grasslands, four of which were in the burned wooded grassland area and eight in the unburned area. Six transects were established in bushland habitat and four each in Acacia mellifera and Commiphora africana bushed woodlands. All transects established in the reserve were 200m long. The herbaceous layer sampling procedures were applied within the four previously identified and distinct vegetation types to establish the characteristic associations of herbaceous layer.

Quadrat sampling technique was adopted where 1x1m quadrats were used for sampling of herbaceous layer in the reserve. A quadrat was randomly placed within each 50m section along each transect. All transects were selected randomly within each vegetation type from a grid map. Individual dicots and grass species were enumerated in each quadrat. Each quadrat was later clipped and individual species separated. Their wet weight was immediately determined by use of a hand held balance, dried to a constant weight at 800c in the laboratory and their oven-dry weight recorded using an electronic balance. The data were analyzed for species composition, density frequency and results grouped by vegetation types. The results for wooded grasslands were further categorized in relation to management interventions that occurred through burning. The Shannon-Wiener diversity indices were tested for significant differences using a t-test (Zar, 1974). The density and frequency of the


herbaceous species were calculated using similar formulae as discussed under woody species section (Cox, 1990).

3.3 Results

3.3.1 Herbaceous species composition The herbaceous data was analyzed for species composition, biomass, density and frequency and the results grouped by vegetation types. The results of the wooded grasslands were further categorized in relation to management interventions that occurred through burning. Tables 6 to 8 show the species composition of dicot and grasses in each vegetation type, their respective oven-dry weight and frequency. The results also show the quantitative composition of dicots in relation to grasses in each vegetation types.

3.3.2 Wooded grasslandsIn the unburned wooded grasslands (Table 6) shows that Sehima nervosum, had a mean dry biomass of 40.3gm-2 followed by Andropogon schirensis at 15.3gm-2. The burned area generally had lower total mean biomass for grasses at 6.7gm-2 compared to 11.1gm-2 of the unburned wooded grassland. Themeda triandra, a highly nutritive grass species tended to increase in biomass at 8.5gm-2 in the wooded grasslands after the burn. The Indigofera sp. registered the highest biomass among the herbaceous dicots. This species had a mean biomass of 9.8gm-2 in burned wooded grassland, which was higher than in the unburned area at 0.67gm-2. The grasses had a relatively higher biomass at 60.89gm-2 (81%) compared to herbaceous dicots at 14.28gm-2 (19%) in the burned area (Figure 14). Similarly the grass biomass at 89.1gm-2 (90%) far exceeded that of the dicots at 9.9gm-2, which contributed only 10% of the total herbaceous biomass in the unburned wooded grassland (Figure 14).

Sehima nervosum and Heteropogon contortus were the main grass species most common in both burned and unburned wooded grassland as evidenced by their high frequency values (Table 6). Tephosia pumila and Endostemon teleticaulis were the two dicots most frequently encountered in the burned and unburned wooded grasslands respectively.

3.3.3 Acacia mellifera bushed woodlandHerbaceous layer in the Acacia mellifera bushed woodland vegetation was dominated by dicot species compared to grass species (Table 7). The grasses and dicots contributed 36% and 64% of the total oven-dry biomass in this habitat respectively (Figure 15). Entropogon macrostachyus had a mean biomass of 1.8gm-2 followed Cenchrus ciliaris at 1.7gm-2, while the least was Heteropogon contortus at 0.7gm-2 (Table 7). The dicots biomass was dominated by that of Eragrostis caespitosa at 3.6gm-2 followed by that of


Table 6: Wet season grass and dicot species composition, biomass and frequency in burned and unburned wooded grasslands. G – Grass species; D - Dicots

Type Burned area Unburned areaSpecies Mean dry

Biomass (gm-

2)

Frequency Mean dry Biomass(gm-2)

Frequency

Andropogon distachyus G 11.66 0.13Andropogon schirensis G 7.47 0.22 15.28 0.28Bothriochloa bladhii G 4.19 0.11Cenchrus ciliaris G 3.33 0.11Eragrostis caespitosa G 1.13 0.17 6.59 0.19Heteropogon contortus G 12.47 0.39 12.96 0.3Hyperthelia dissolute G 9.71 0.28 0.54 0.06Panicum maximum G 2.62 0.06Sehima nervosum G 11.19 0.5 40.27 0.59Sorghum purpureo-sericeum G 0.38 0.03Themeda triandra G 8.46 0.11 1.25 0.03

Cassia fallacina D 0.14 0.06Dyschoriste hildebradtii D 0.19 0.06 0.95 0.15Endostemon teleticaulis D 1.44 0.17 1.72 0.41Helichrysum sp D 0.03 0.06 0.02 0.03Hermannia oliveri D 0.04 0.06Indigofera sp D 9.83 0.17 0.67 0.13Indigofera volkensii D 0.36 0.03Phyllanthus maderasperensis D 0.04 0.11 0.02 0.03Ruellia patula D 1.43 0.17 6.03 0.16Spermacoce sphaerostigma D 0.01 0.06Tephrosia pumila D 1.18 0.22 0.07 0.03Tragia plukenetii D 0.05 0.03Trimfetta flavescens D 0.25 0.06 0.00 0.03Vernonia aemulans D 0.11 0.03Vigna sp D 0.08 0.03

Hibiscus calyphyllus at 2.1gm-2. Entropogon macrostachyus and Setaria pumila were the most frequently encountered grass species in Acacia mellifera bushed woodland. Hermannia uhligii, Hibiscus calyphyllus, Endostemon tereticaulis, Barleria eranthemoides, Barleria micrantha and Aspilia pluriseta were the most frequently encountered dicots in this vegetation type. The total grasses biomass at 8.1gm-2 (36%) was relatively lower than of the dicots at 14.51gm-2, which constituted 64% of the total biomass in this vegetation type (Figure 14).


Figure 14: Wet season grasses and dicots dry biomass in burned and unburned wooded grasslands

3.3.4 Commiphora africana bushed woodlandIn the Commiphora africana bushed woodland, Enteropogon macrostachyus had a mean biomass of 6.5gm-2 followed by Setaria pumila at 1.4gm-2 while Cenchrus ciliaris had the least biomass of 0.2gm-

2 (Table 7). These first two species had a combined oven-dry biomass of 91% of total grass biomass in this habitat, and were also the most frequently encountered.

Barleria micranthus had a mean biomass of 7.2gm-2 followed by B. eranthemoides at 2.4gm-2, and had both a combined oven-dry biomass of 63% of the total dicot biomass in Commiphora africana bushed woodland. The two dicots were also the most frequently encountered species in this habitat. Dicots and grass species biomass accounted for 64% (15.3gm-2) and 36% (8.6gm-2) of the total biomass respectively (Figure 15).

3.3.5 BushlandIn the bushland habitat Sehima nervosum had a mean biomass of 4.9gm-2 followed by Setaria pumila at 4.1gm-2 while Cenchrus ciliaris had the least biomass of 0.02gm-2. S. nervosum and S. pumila had a combined biomass of 57% of total grass biomass in this habitat (Table 7). Barleria micrantha had a mean biomass of 3.2gm-2 followed by B. eranthemoides at 0.89gm-2 and Commelina benghalensis at 0.88gm-2. Generally, grasses and dicots accounted for 69% (15.8gm-2) and 31% (7.1gm-2) of the total biomass in bushland vegetation type respectively (Figure 15). Setaria pumila was the most abundant grass species, while Commelina benghalensis, Barleria micrantha, Hibiscus calyphyllus and B. eranthemoides were the most frequently encountered dicots in this habitat.


Figure 14: Wet season grasses and dicots dry biomass in burned and unburned wooded grasslands

0

10

20

30

40

50

60

70

80

90

100

Burnt Unburnt

Treatment

Bio

mas

s (g

m-2

)

Grasses Dicots

Table 7: Wet season grass and dicot species composition, biomass and frequency in three vegetation type. G – Grass species D - Dicots

A. mellifera habitat

C. africana habitat Bushland habitat

SpeciesType Mean

dry Biomas (gm-2)

Frequency

Mean dry Biomass (gm-2)

Frequency

Mean dry Biomass (gm-2)

Frequency

Brachiaria deflexa G 1.54 0.13Brachiaria laersioides G 0.30 0.04Cenchrus ciliaris G 1.72 0.06 0.16 0.06 0.02 0.04Dactyloctenium germinatum G 0.08 0.04Digitaria milanjiana G 0.76 0.06 1.38 0.09Digitaria scalurum G 0.96 0.06Enteropogon macrostachyus G 1.82 0.13 6.46 0.19Eragrostis caespitosa G 0.64 0.13 3.38 0.13Heteropogon contortus G 0.70 0.06 0.19Sehima nervosum G 4.86 0.13Setaria pumila G 1.08 0.13 1.37 4.14 0.48Sporobolus festivus G 0.04 0.04Themeda triandra G 1.15 0.06Abutilon fruticosum D 0.47 0.06Acalypha psilostachya D 0.16 0.06 0.73 0.13Achyranthes aspera D 0.08 0.06Acalypha volkensii D 0.04 0.13Asparagus flagellaris D 0.69 0.06 0.10 0.04Aspilia pluriseta D 0.00 0.31 0.04 0.25 0.00 0.09Barleria eranthemoides D 1.73 0.38 2.41 0.63 0.89 0.26Barleria micrantha D 1.52 0.31 7.16 0.56 3.16 0.30Brachiara deflexa D 1.87 0.44Cassia absus D 0.03 0.06Cissampelos mucronata D 0.04 0.06Cissus quadrangularis D 0.42 0.06Commelina benghalensis D 0.24 0.19 1.12 0.50 0.88 0.35Crabbea velutina D 0.27 0.13 0.02 0.04Endostemon tereticaulis D 0.39 0.38 0.00 0.04Eragrostis caespitosa D 3.56 0.19Helinus intergrifolia D 0.23 0.13 0.30 0.04Hermania uhligii D 0.18 0.50 0.00 0.13Hibiscus calyphyllus D 2.14 0.38 1.84 0.38 0.00 0.13Indigofera volkensii D 0.28 0.06Ipomea involucrate D 0.04 0.04Justica sp D 0.08 0.06 0.00 0.06Leucaus martinicensis D 0.29 0.06 0.03 0.04Plectranthus caninus D 0.16 0.06Polygala sadebeckiana D 0.66 0.31Pupalia lappacea D 0.52 0.25 0.41 0.19 0.01 0.09Rhynchosia schimperi D 0.16 0.13


Spermacoce sphaerostigma D 0.12 0.06 0.10 0.09Tephrosia pumila D 0.04 0.06 0.42 0.09Trimfetta flavescens D 0.16 0.38 0.00 0.06 0.00 0.04Vernonia galamensis D 0.19 0.06 0.28 0.13 0.28 0.13

Figure 15: Wet season grasses to dicots dry bimass in three vegetation types in the reserve

3.3.6 Wet season herbaceous species density and diversity indicesHypethelia dissoluta, Heteropogon contortus, Brothriochloe bladhii, Andropogon schirensis and Selima nervosum were the grass species with the highest density values in the burned area of wooded grasslands (Table 8). The herb species in this habitat had density values less than 1.00 with Cassia fallacia and Tephrosia pumila having higher density values compared to the rest (Table 9). Sehima nervosum grass species had the highest density values in the unburned wooded grasslands followed by Andropogon schirensis and Andropogon distachyus (Table 8). Endostemon teleticaulis was the only herb species that registered a comparatively higher density compared to other herb species in this habitat (Table 9). All grass species in Acacia mellifera bushed woodland registered low-density values less than 1.00 (Table 9). Leucaus martinicensis herb species shows a higher density in this habitat and was closely followed by Hibiscus calyphyllus and Commelina benghalensis (Table 9).


0

2

4

6

8

10

12

14

16

18

A. mellifera bushed woodland C. africana bushed woodland Bushland

Vegetation types

Bio

mas

s (g

m-2

)

Grasses Dicots

Table 8: Wet season grass species density estimates for vegetation types in the reserve

SpeciesVegetation typeBurned Unburned Aca mel Comi afri BushlandDensity (m2)

Density (m2)

Density (m2)

Density (m2)

Density (m2)

Andropogon distachyus 1.16Andropogon schirensis 1.39 1.22Bothriochloa bladhii 1.72Brachiaria deflexa 1.92Brachiaria laersioides 2.08Cenchrus ciliaris 0.22 0.06 0.06 0.04Dactyloctenium germinatum 0.04Digitaria milanjiana 0.13 2.46Digitaria scalurum 0.31Enteropogon macrostachyus 0.69 6.38Eragrostis caespitosa 0.28 0.38 0.38 0.50Heteropogon contortus 1.78 0.81 0.31Hyperthelia dissoluta 2.17 0.16Panicum maximum 0.78Sehima nervosum 1.17 2.81 0.38Setaria pumila 0.44 7.56 15.42Sorghum purpureo-sericeum 0.66Sporobolus festivus 0.13Themeda triandra 0.56 0.16 0.31Aca mel – Acacia mellifera bushed woodlandComi afri – Commiphora africana bushed woodlandBurned – Burned wooded grasslandUnburned – Unburned wooded grasslandBushland – Bushland habitat

In Commiphora afaricana bushed woodland vegetation type, Setaria pumila and Enteropogon macrostachyus were the only two grass species that had the highest density values compared to the others (Table 8). Dicot species that were recorded to have density values above 1.00 were Commelina benghalensis, Barleria micrantha, Vernonia galamensis, Spermacoce sphaerostigma, Barleria eranthemoides and Hibiscus calyphyllus (Table 9). Setaria pumila had a higher density value in the bushland vegetation type compared to other grass species (Table 8). Other grass species that registered higher densities were Digitaria milanjiana, Brachiaria laersioides and Brachiaria deflexa. Acalypha psilostachya, Commelina benghalensis, Acalypha volkensii and Spermacoce sphaerostigma were the only dicot species that registered density values above 1.00 (Table 9).


Table 9: Wet season dicots density estimates for vegetation types in the reserve

SpeciesVegetation typeBurned Unburned Aca mel Comi afri BushlandDensity (m2)

Density (m2)

Density (m2)

Density (m2)

Density (m2)

Abutilon fruticosum 0.50Acalypha psilostachya 1.94 6.50Acalypha volkensii 1.42Achyranthes aspera 0.44Asparagus flagellaris 0.06 0.04Aspilia pluriseta 0.75 0.56 0.08Barleria eranthemoides 1.50 1.44 0.75Barleria micrantha 0.94 3.00 0.75Cassia absus 0.06Cassia fallacina 0.78Cissampelos mucronata 0.06Cissus quadrangularis 0.06Commelina benghalensis 2.31 3.25 1.46Crabbea velutina 0.44 0.08Dyschoriste hildebradtii 0.06 0.19Endostemon teleticaulis 0.33 1.28 0.56 0.04Eragrostis caespitosa 1.19Helichrysum sp 0.33 0.09Helinus intergrifolia 0.19 0.13Hermannia oliveri 0.11Hermannia uhligii 1.38 0.13Hibiscus calyphyllus 2.38 1.19 0.17Indigofera sp 0.44 0.41Indigofera volkensii 0.03 0.13Ipomea involucrata 0.08Justica sp 0.06 0.06Leucaus martinicensis 4.75 0.17Phyllanthus maderasperensis 0.72 0.13Plectranthus caninus 0.06Polygala sadebeckiana 1.00Pupalia lappacea 0.63 0.38 0.13Rhynchosia schimperi 0.33Ruellia patula 0.22 0.38Spermacoce sphaerostigma 0.44 1.88 1.33Tephrosia pumila 0.72 0.03 0.13 0.46Tragia plukenetii 0.03Trimfetta flavescens 0.22 0.22 1.13 0.06 0.13Vernonia aemulans 0.41Vernonia galamensis 1.81 2.69 0.71Vigna sp 0.03Aca mel – Acacia mellifera bushed woodland Burned – Burned wooded grasslandComi afri – Commiphora africana bushed woodland Bushland – Bushland habitatUnburned – Unburned wooded grassland


The Acacia mellifera bushed woodland habitat followed by the burned area of wooded grassland registered the highest diversity indices compared to the other vegetation types in Mwea National Reserve (Table 10). The habitat with the least herbaceous diversity was Commiphora africana bushed woodland, which closely followed that of the bushland vegetation type. The herbaceous layer diversity indices show significant differences between vegetation types (Table 10) with the exception of that between Commiphora africana bushed woodland and bushland vegetation type.

Table 10. Wet season Shannon-Wiener diversity indices and their critical t-test values between vegetation types

Vegetation type

Burned Unburned Aca. mel. Comi. Afri. Diversity index

Burned 1.17Unburned 3.98*

(599)1.05

Aca. mel. 3.66* (635)

7.43* (701) 1.27

Comi. Afri. 10.52* (568)

5.15* (627) 14.96* (889)

0.91

Bushland 8.28* (803)

3.67* (847) 12.14* (1185)

1.22 (1534) 0.94

* - Significant critical values Degrees of freedom (df) in parenthesisBurned - Burned wooded grasslandUnburned - Unburned wooded grassland Aca. mel. – Acacia mellifera bushed woodlandComi. Afri –Commiphora africana bushed woodland Bushland – Bushland vegetation type

3.4 DiscussionThe wooded grasslands had several invasive herbaceous and woody species mainly common to woodlands and the bushland. These invasives are reducing the available pasture area, pasture quality and quantity of food resources to herbivores. However, sporadic fires in the wooded grasslands seem to have improved the grass species composition and biomass. This treatment was mainly through accidental fires, which were occurring and starting sporadically in grassland areas near the human settlements.

Savanna grassland are known to be maintained by rainfall, herbivores, soils and fires (Sinclair, 1975; Norton-Griffiths, 1979; Deshmukh and Baig, 1983; Deshmukh, 1984; Broutton et al., 1988a; Broutton et al., 1988b; Dublin, et al., 1990, Dublin, 1995, Mwangi and Western, 1998). Management of grasslands is better achieved by use of fires with all other conditions remaining constant. For instance it was observed that fire by itself in the Serengeti-Mara ecosystem in the 1960s could hold woody species recruitment rates well below adult mortality rate even at burning rates which were conservative (Sinclair, 1975; Norton-Griffiths, 1979). Conversely, even under the most extreme conditions of elephant-related tree mortality, elephants were not able to reduce woody species recruitment rates below adult mortality rates causing a decline in woodland vegetation (Dublin et al. 1990).

The wooded grassland invasion by woody plants and herbaceous plants continue to decrease the quality of pasture for grazers. Elephants alone may not quickly reverse the trend even if they happen to use the wooded grasslands as their key habitat in future. Usage of fires, its timing and frequency are


the main solutions in controlling the current encroachment of wooded grasslands by woody and herbaceous plants. A fire management programme should also take into account the future increase and effect of elephant browsing and other mammalian species trampling of vegetation in the reserve. Elephant browsing and other mammalian species trampling and browsing were hypothesized to hold the Serengeti-Mara within the current new state after fires in 1960s and 1970s, where woody species recruitment rate are below those necessary to balance adult tree mortality rates (Dublin et al. 1990).

CHAPTER 4: MAMMALIAN SPECIES COUNT, HABITAT USE AND INTERACTION IN MWEA NATIONAL RESERVE

4.1 IntroductionMwea National reserve vegetation structure precludes visual wildlife census techniques because in most of the vegetation types (Acacia mellifera bushed woodland, the riverine, Commiphora africana bushed woodland, the bushland and vegetation transition zones) visibility is reduced to between 5 and 10m by the thick undergrowth. Translocation of a family of 23 elephants to Tsavo East National Park in 1996 traumatized the elephants that were left behind, which are usually shy and cryptic in their behaviour. This characteristic behaviour further reduces census enumerator’s chances of counting the elephants directly. Poaching of animals for subsistence has reduced the other mammalian species in the reserve to low densities making it impossible to conduct a direct count to determine their numbers. Due to these direct count limitations, an indirect technique using mammalian droppings was used to determine their population size, habitat utilization and distribution within the reserve.

The study aimed at establishing the relative density of mammalian species utilizing various habitats and whether their habitat use is influenced by the distribution of elephants in the reserve. The dung density for each mammalian species is used as a index to estimate the level of occupancy of each vegetation type.

4.2 Methods

4.2.1 Mammalian species countsIndirect animal counts in Mwea National reserve were conducted at the middle of the dry season and end of the wet season. The frequency of encounter of dung piles provides indices of habitat utilization by various species (Komer and Brotherton, 1997; Koster and Hart, 1998). Fecal pellets were identified and assigned to various species depending on their shape and size (Hashim and Deffula, 1996). Transects were established in Acacia mellifera bushed woodland, Commiphora africana bushed woodland, bushland habitat, wooded grasslands, riverine vegetation type and the transition zone between these vegetation types. The riverine and the transition zones vegetation were considered as a separate vegetation type. The dung belt transects were 10m wide running the length of transects between 300-500m long. The results were expressed as dung pile per hectare. The dung density per hectare was used as an index of distribution, utilization and abundance. Testing for differences in mammalian species distribution between seasons was conducted using t-test for independent samples. The Tukey-B post range test was used to test for significant differences in mammalian abundance and distribution between vegetation types. G-test analysis for goodness of fit was used to determine association between elephant and other mammalian species in both dry and wet seasons.

4.3 Results

4.3.1 Seasonal herbivore densities and distribution Figures 16 to 21 show the large herbivore dung densities in the reserve during the dry and the wet seasons. The dung densities were analyzed with respect to vegetation types. The dung densities were


used as an index of habitat occupancy and preference by various species. The results show that the dung densities for all species were generally more per hectare during the dry season compared to the wet season.

4.3.2 Acacia mellifera bushed woodlandFigure 16 shows the dung densities for various large herbivores that were enumerated in the A. mellifera bushed woodland vegetation type. In exception of the warthog, waterbuck, giraffe and zebra, all other herbivore species encountered in the reserve utilized this vegetation type. The impala and the duiker had a higher occupancy in this vegetation type compared to others during the dry and the wet seasons. The rest of the species had dung densities of less than 20/ha each in both the dry and the wet seasons. The baboon had a significantly higher mean dung density at 17.95/ha (t8 = 3.69; P<0.05) during the wet season (Table 11) while the impala mean dung density at 106.68/ha was found to be significantly higher during the dry season (t10 = 2.98; P<0.05). The rest of the herbivore species were not found to have significant seasonal preference for A. mellifera bushed woodland.

Figure 16: Dung density as an index of utilization of the Acacia mellifera bushed woodland by large herbivores during the dry and wet seasons


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Figure 17: Dung density as an index of utilization of the Commiphora africana bushed woodland by large herbivores during the dry and wet seasons

4.3.3 Commiphora africana bushed woodlandCommiphora africana bushed woodland (Figure 17) had a high herbivore occupancy compared to other vegetation types as evidenced by high dung densities, which were above 20 dung piles per hectare for most species. The dung densities for most herbivores were generally more per hectare during the dry season compared to the wet season. The habitat was most preferred by the elephant in both seasons and in the dry season by both the impala and the warthog. Herbivore occupancy in this vegetation type between seasons did not change significantly except for the duiker (t6 = 2.59; P<0.05) and the sunni (t6 = 4.21; P<0.05). These species had a higher mean dung density at 26.82/ha and 21.98/ha respectively in the dry season compared to the wet season (Table 11). Other herbivore species did not show seasonal preference for this habitat.


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Table 11: Dry and wet seasons mean ±SE dung density for herbivores in the A. mellifera and the C. africana bushed woodlands

Acacia mellifera bushed woodland dung densitySpecies Dry season dung

density - mean ± SEWet season dung density - mean ± SE

t-value P-Value

Baboon 10.66±1.25 17.95±1.53 t8 = 3.69* P<0.05Bushbuck 18.87±3.75 7.66±1.35 t10 = 2.03 P>0.05Buffalo 15.01±4.20 8.09±1.12 t7 = 1.78 P>0.05Dik-dik 14.01±5.62 6.41±1.16 t7 =1.18 P>0.05Duiker 34.63±9.27 24.50±6.98 t10 = 0.81 P>0.05Elephant 17.70±3.99 15.42±3.23 t9 = 0.43 P>0.05Impala 106.68±19.84 34.71±4.65 t10 = 2.98* P>0.05Sunni 17.49±4.97 6.90±1.53 t7 = 2.25 P>0.05

Commiphora africana bushed woodland dung densityBaboon 32.59±6.91 27.23±3.86 t9 = 0.55 P>0.05Bushbuck 35.35±16.15 14.21±5.95 t8 = 1.02 P>0.05Dik-dik 9.25±1.44 11.66±3.96 t9 = 0.69 P>0.05Duiker 26.85±8.43 1.92±0.96 t6 = 2.59* P<0.05Elephant 62.58±25.21 53.28±17.83 t8 = 0.27 P>0.05Impala 60.66±20.61 16.65±2.36 t8 = 1.70 P>0.05Sunni 21.98±3.46 6.51±1.24 t6 = 4.21* P<0.05Waterbuck 25.83±16 10.28±3.26 t7 = 0.85 P>0.05Warthog 43.25±24.81 7.22±1.91 t7 = 1.65 P>0.05* - Denotes significant difference between pairs

4.3.4 Bushland vegetation typeThe bushland habitat was generally preferred by herbivores during the dry season compared to the wet season except for elephants, as evidenced by their dung densities (Figure 18). The habitat was significantly more utilized by the bushbuck (t6 = 2.68; P<0.05), the dik-dik (t6 = 2.76; P<0.05) and the warthog (t7 = 11.22; P<0.05) during the dry season (Table 12). Other herbivore species did not show any change in habitat preference between the two seasons. High herbivore dung densities at above 20/ha for most species in the bushland in either of the seasons show the importance of this habitat as is the case for C. africana bushed woodland.

The elephant, the impala and the baboon had this vegetation type as their principal habitat in both seasons. The buffalo, the giraffe and the zebra were, however, conspicuously absent in 4.3.5 Riverine vegetation type


Figure 18: Dung density as an index of utilization of the bushland habitat by large herbivores during the dry and wet seasons

Figure 19: Dung density as an index of utilization of the riverine vegetation type by large herbivores during the dry and wet seasons


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The riverine vegetation type was preferred by a few herbivores during the dry and the wet seasons (Figure 19). The habitat was not significantly utilized by any of the species among seasons, although there was a proportionately higher number of impala found here during the dry season as evidenced by their dung density (Table 12). It was a principal habitat for baboons during the dry and the wet seasons. Other herbivores in this habitat had dung densities fewer than 20 dung piles per hectare during the two seasons. A higher proportion of herbivores found in the A. mellifera bushed woodland, C. africana bushed woodland and the bushland were not represented in this habitat.

Table 12: Dry and wet seasons mean ±SE dung density for herbivores in the bushlan and the riverine vegetation types

Bushland habitat dung densitySpecies Dry season dung

density mean ± SEWet season dung density - mean ± SE

t-value P-Value

Baboon 47.33±20.34 29.78±5.9 t6 = 1.04 P>0.05Bushbuck 15.05±2.06 7.59±1.87 t6 = 2.68* P<0.05Dik-dik 16.96±3.54 6.03±1.77 t6 = 2.76* P<0.05Duiker 43.72±12.96 17.03±6.10 t7 = 2.00 P>0.05Elephant 44.19±21.33 90.65±36.15 t6 = 1.11 P>0.05Impala 44.08±26.63 34.10±6.97 t6 = 0.36 P<0.05Sunni 10.09±2.48 9.24±1.34 t6 = 0.30 P<0.05Waterbuck 18.23±4.37 7.64±2.49 t6 = 2.11 P>0.05Warthog 52.53±3.44 9.19±2.12 t7 = 11.22* P<0.05

Riverine vegetation type dung densityBaboon 45.84±27.56 44.98±26.66 t7 = 0.02 P>0.05Buffalo 14.13±6.41 5.77±0.90 t6 = 1.29 P>0.05Duiker 7.88±0.99 19.08±8.62 t6 = 1.29 P>0.05Elephant 17.48±4.99 25.16±9.83 t8 = 0.70 P>0.05Impala 80.89±68.51 13.62±3.79 t7 = 1.12 P>0.05Warthog 8.21±2.19 8.60±2.73 t7 = 0.11 P>0.05* - Denotes significant difference between pairs

4.3.6 Wooded grasslandsThe wooded grasslands were principal habitat for the giraffe and the zebra and were not found in any other vegetation type in the reserve (Figure 20). This vegetation type was also an important habitat for the impala and the buffalo. The four herbivore species were most pre-dominant in this vegetation type as shown by their dung densities of about 20 dung piles per hectare. Conversely, the bushbuck and the sunni occupancy was low in this habitat. Herbivore occupancy in this habitat did not show any significant difference between the dry and the wet seasons (Table 13).


Figure 20. Dung density as an index of utilization of the wooded grasslands by large herbivores during the dry and wet seasons

Figure 21. Dung density as an index of utilization of the transition zone by large herbivores during the dry and wet seasons


Figure 20: Dung density as an index of utilization of the wooded grasslands by large herbivores during the dry and wet seasons

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4.3.7 Transition zoneHerbivore species were poorly represented in this habitat compared to all other habitats in the reserve (Figure 21). The only herbivores found to prefer this habitat were the baboon, the elephant and the impala. They, however, had proportionately higher dung densities per hectare during the dry season compared to the wet season, although no significant differences were recorded in their occupancy between the two seasons (Table 13).

Table 13: Dry and wet seasons mean ±SE dung density for herbivores in the transiton zone and the wooded grasslandsTransition zoneSpecies Dry season dung

density - mean ± SEWet season dung density - mean ± SE

t-value P-Value

Baboon 28.56±15.22 8.14±1.83 t8 = 1.33 P>0.05Elephant 12.16±3.17 10.06±1.63 t7 = 0.63 P>0.05Impala 41.75±16.54 10.70±3.08 t7 = 2.08 P>0.05Wooded grasslands

Bushbuck 7.38±2.26 6.66±2.36 t10 = 0.20 P>0.05Giraffe 24.40±5.57 38.63±8.72 t15 = 1.38 P>0.05Impala 35.61±18 47.29±22.57 t15 = 0.37 P>0.05Sunni 7.60±5.91 8.91±6.47 t8 = 0.33 P>0.05Zebra 29.17±9.46 66.57±18 t15 = 2.01 P>0.05

4.3.8 Herbivore habitat preferences and distributionThe mean dung densities of herbivores did not show any significant difference in their habitat occupancy among vegetation types during the dry season, except for sunni (Table 14). The mean dung density for the sunni at 21.98/ha in Commiphora africana bushed woodland was only significantly higher than in the wooded grasslands (F3,13 = 3.78; P<0.05). The buffalo shows preference for wooded grasslands during the wet season (t8 = 3.29; P<0.05) compared to the A. mellifera bushed woodland (Table 14). Similarly, the elephant mean dung density of 90.65/ha in the bushland habitat was significantly higher than in A. mellifera bushed woodland, the riverine vegetation type and the transition zone (F4,18 = 3.98; P<0.05). These significant differences indicate preferences in elephant occupancy of the bushland habitat during the wet season. Other herbivores did not show preference of any of the vegetation types in the reserve in terms of their occupancy during the wet season (Table 14).

4.3.9 Elephant interaction with other mammalian speciesTable 15 shows the G-test critical values of elephant association with other mammalian species in four vegetation types, the A. mellifera, C. africana bushed woodlands, bushland and riverine vegetation types. These were the main habitats commonly utilized by elephants in the reserve. The tests were performed to determine whether the elephants


Table 14: Dry and wet seasons meanSE dung density as a measure of herbivore occupancy for various vegetation types in Mwea NR

Species A. mellifera bushed woodland

Bushland habitat

C. africana bushed woodland

Riverine vegetation type

Transition zone

Wooded grasslands

F-value P-value

Mean dung density during the dry seasonBaboon 10.661.25 47.3320.34 32.596.91 45.8427.56 28.5615.22 F4,19 =0.99 P>0.05Bushbuck 20.473.88 20.055.25 35.3516.15 7.392.26 F3,22 = 2.12 P>0.05Buffalo 154.20 14.136.41 26.719.57 F2,14 =0.60 P>0.05Dik-dik 145.62 14.414.38 9.791.75 F2,14 = 0.56 P>0.05Duiker 34.639.27 43.7212.96 26.938.42 7.880.99 F3,15 = 2.22 P>0.05Elephant 18.363.43 44.1921.33 62.5825.21 17.484.99 12.163.17 F4,21 = 2.07 P>0.05Impala 106.6819.84 44.0826.63 60.6620.61 80.8968.51 32.4619.25 35.9419.72 F5,30 = 1.16 P>0.05Sunni 17.494.97 10.092.47 21.983.46 7.602.64 F3,13 = 3.78* P<0.05Warthog 52.533.44 43.2524.81 8.095.23 F2,7 = 1.25 P>0.05Waterbuck 18.224.37 25.8315.99 t7 = 0.41 P>0.05

Mean dung density during the wet seasonBaboon 17.951.53 29.785.89 27.233.86 44.9826.66 8.141.83 F4,19 = 1.18 P>0.05Bushbuck 7.661.35 7.591.87 16.737.63 6.662.35 F3,11 = 1.63 P>0.05Buffalo 8.091.12 19.313.23 t8 = 3.29* P<0.05Dik-dik 6.411.16 6.031.77 11.663.96 F2,9 = 1.47 P>0.05Duiker 24.506.98 17.036.09 4.990.96 19.088.62 F3,14 = 1.56 P>0.05Elephant 15.423.28 90.6536.15 53.2817.83 25.169.85 10.061.63 F4,18 = 3.98* P<0.05Impala 34.714.65 34.106.97 16.652.35 13.613.79 10.73.08 47.2922.57 F5,22 = 1.94 P>0.05Sunni 6.901.53 9.241.34 6.521.24 8.912.89 F3,14 = 0.46 P>0.05Warthog 9.192.12 7.221.91 8.602.73 F2,12 = 0.20 P>0.05Waterbuck 7.642.49 10.283.26 t6 = 0.65 P>0.05


influenced the distribution of other mammalian species during both the dry and the wet seasons. Both wet and dry season comparisons were conducted using dung counts in each vegetation type as a measure of habitat use by each species. The distribution of other mammalian species in the reserve was found to be independent of that of the elephants in the dry season, except that of the bushbuck, which corresponded, with that of the elephants (Table 15). The situation did not change much during the wet season. The distribution of most mammalian species during the wet season was not found to closely associate with that of the elephants (Table 15). The dik-dik, the sunni and the waterbuck were the only species found to closely associate with elephants in their habitat utilization during the wet season.

Table 15: G-test critical values in elephant habitat interaction with other mammalian species in the reserve (3df).

Species Dry season G-value

P-value Wet season G-value

P-value

Baboon 26.39* P<0.05 85.66* P<0.05Bushbuck 7.37 P>0.05 192.5* P<0.05Buffalo 51.12* P<0.05 13.3* P<0.05Dik-dik 14.32* P<0.05 4.6 P>0.05Duiker 59.82* P<0.05 13.35* P<0.05Impala 80.59* P<0.05 507.95* P<0.05Sunni 34.91* P<0.05 5.06 P>0.05Waterbuck 9.99* P<0.05 1.57 P>0.05Warhog 7.82* P<0.05 23.53* P<0.05

- Denotes significant difference in elephant and species distribution

4.4 DiscussionThere were no significant associations (P>0.05) between elephants and other mammalian species during the wet season and the dry season. The bushbuck, however, showed close association with the elephant during the dry season while the dik-dik, the sunni and the waterbuck were closely associating with the elephant during the wet season. Lack of strong association between the elephants and other mammalian species is a clear indication that elephants do not influence habitat use by other mammalian species. Similarly, very few animals showed seasonal preference among the various habitats in Mwea National Reserve. Seasonal changes in elephant distribution and habitat selection has been well documented elsewhere in African (Laws et al., 1975; Williamson, 1975; Eltringham, 1977; Leuthold, 1977; Western and Lindsay, 1984; Lewis, 1986). As a key stone species, elephants will also influence the distribution of other mammalian species in a given ecosystem (Western, 1989). Other studies have also established that water availability and distribution are the most important factors affecting or limiting elephant local movement (Laws, 1970; Weir, 1972; Poche, 1974; Kerr and Fraser, 1975). The elephant distribution and habitat selection coincide with seasonal climatic changes and the corresponding changes in food and water availability (Viljoen, 1989). The seasonal use of habitat is probably an important mechanism of survival and optimum utilization of resources, while at the same time reducing the impact on dry season habitat (Viljoen, 1989).

Mwea NR elephant population used to exhibit these seasonal movements before the erection of the electric fence in 1998. These movements probably conferred recovery time for vegetation resulting in reduced damage on vegetation in the reserve. Curtailment of these movements by the fence and subsequent increase in elephant density in the reserve may in the future exacerbate elephant impact on vegetation. Currently, however, there are no signs of serious elephant related


impacts on vegetation as evidenced by high proportion of seedlings (<1m) woody plants (see chapter 2). Similarly, the availability and distribution of water is not and will not in the future be a critical factor in elephant distribution and movement within the MNR. This observation will be true as long as the reserve will be endowed with the current large water frontage, where animals walk a short distance in search of water. Most of the other mammalian species did not exhibit seasonal changes in their distribution within the reserve. The short distance moved in search of water may probably also explain this. This observation may further be supported by the fact that the year round lush riverine vegetation was not significantly selected as the preferred habitat in the dry season (P>0.05). The animal were using the riverine vegetation as well as other vegetation types further away probably due to accessibility of water along the Thiba and Tana rivers during the dry season.


5.0 References

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3 · web viewsehima nervosum and heteropogon contortus were the main grass species most common in...

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