analysis of biodiversity and biomass in the ankasa
TRANSCRIPT
C. Consalvo1, L. Belelli Marchesini1, R. Valentini1
1 Department of Forest Science and Resources (DISAFRI), University of Tuscia - Viterbo, ITALY
For more information:
Claudia Consalvo
University of Tuscia - Department of Forest Environment and Resources
Via De Lellis, 01100 Viterbo- Italy
phone ++39 0761 357412
Analysis of biodiversity and biomass in the Ankasa
Resource Reserve, Ghana
The Ankasa Resource Reserve
The Ankasa Conservation Area lies in Southwest Ghana on the border with
the Ivory Coast. It covers 509 km2 and includes the Nini-Suhien National
Park (166 km2) and the Ankasa Resource Reserve (343 km2). Ankasa
represents the most biodiverse rain forest in Ghana and unlike the Nini-
Suhien National Park is not fully protected.
The climate of the area is characterized by a distinctive bi-modal rainfall
pattern occurring from April to July and September to November. The
average annual rainfall is 1700 to 2000 mm. Mean monthly temperatures are
typical of tropical lowland forest and range from 24°C to 28°C. Relative
humidity is generally high throughout the year, being about 90% during the
night falling to 75% in early afternoon.
The topography is characterized by rugged, deeply divided terrain in the north
and west with flatter swampy ground associated with the Suhien watershed in
the East. Its maximum elevation is 150 m, though most lies below 90 m.
UNIVERSITY OF CAPE COAST
Materials and methodsTwo transects were demarcated for a total surface of 2 ha. The height of the
trees was estimated with Vertex laser V 1.6 or with a visual estimation. The
diameter of the trees was taken at 1.30 m above the ground. All the plants with
diameter over 5 cm were measured in every subplot.
Aim
Tropical rainforests play a crucial role for the biosphere and therefore are a
natural reserves of biological diversity and store large amounts of carbon
playing a major role in the global carbon budget.
This study was conducted in the framework of CarboAfrica project, and was
aimed at the ecological characterization of the Ankasa tropical forest.
ConclusionDue to the low level of secondary and pioneer species and the high rate of biodiversity, Ankasa reserve can be considered an undisturbed forest. Ankasa is also an
important carbon stocks estimated at 135 t C ha-1 in stand biomass. In light of these results it is clear that the African tropical forests, yet undergoing an impressive
rate of deforestation should be considered with great attention to avoiding the biodiversity loss, and mitigating climate change.
ResultsAlong the sampling area of 2 ha, 38 families, 114 genera and 184 species were found. A total of 1898 plants with a diameter at breast height >5 cm was found
with an average density per hectare of 950 plants. The species were listed into a different categories (Fig. 2). This encapsulates the most of the ‘ecological niche’
of the overall species.
DISAFRIDISAFRIDepartment of Forest Environment and Resources
Dipartimento di Scienze dell’Ambiente Forestale e delle sue Risorse
UNIVERSITY OF TUSCIA
Fig 4 – Ipsometric curve. The structure
of the Ankasa Forest consists of large
diameter trees but with reduced stature
with plants that rarely exceed 40 meters in
height.
Shade-bearers80%
NPLD 8%
Swamp species 2%
Pioneers4%
Unclassified6%
Black6%
Gold9%
Blue16%
Scarlet2%
Red5%
Pink5%
Green45%
Others12%
0
3
6
9
12
15
18
21
24
27
30
33
36
39
42
45
48
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38
Bio
mass
an
d n
um
ber
of
pla
nts
(%)
Classes of diameter (cm)
Biom rel tot freq rel tot
7,5 17,5 27,5 37,5 47,5 57,5 67,5 77,5 87,5 97,5 107,5 117,5 127,5 137,5 147,5 157,5 167,5 177,5 187,5
60 - 100 cm 100 - 195 cm
Number of plants
5 – 60 cm
Fig 2 - Distribution of the number of plants in the
different categories of temperament.
•Pioneers are generally species that benefit from
forest disturbance.
•NPLDs are ‘Non pioneer light demanders’, being
intermediate between the previous and next
categories.
•Shade-bearers are often to be found healthy in the
shady understorey, and rarely benefit from
disturbance
•Swamp species are largely restricted to rivers
and/or swamps.
The basal area per hectare was estimated as 50 ± 11,5 m2 ha-1(average ± dev.st.).
The aboveground biomass was 271 t ha-1 which equals to a carbon stock of 135
t C ha-1 after applying a conversion factor of 0,47 gC/g d.m.
The estimated LAI was 6 ± 1.01 (average ± dev.st.).
The maximum value of LAI in tropical forests
varies from 4 to 7. Phenology in tropical forests is
more related to the water balance rather than to
changes in temperature and solar radiation. In
comparison to other regions, the variation of these
two variables during the year is reduced.
Fig 5 - Distribution of biomass and number
of plants in various classes of diameter. The
plants included in the intermediate diameter
classes are those that have a greater
development in height and providing a
significant contribution to the total biomass.
Into the sampling area, the following issues
were analyzed:
•Biodiversity - Several biodiversity indices
were calculated, including the Genetic Heat
Index (GHI)[1] for estimating the abundance of
rare species in the forest population.
Leaf area index (LAI) - the LAI was
estimated by hemispherical photo process.
Photos were taken with a Nikon D200 camera
(Fig. 1) and with a lens Nikkor fisheye 10.5
mm, every 10 m. The images were processed
with the software CAN-EYE devloped by
INRA-CSE, Avignon, France.
•Biomass - the aboveground biomass was
estimated using an allometric equation
developed for the Wet Evergreen Forests:
Biomass=standing dry biomass (kg)
D=diameter (cm)
H=height (m)
Biomass = exp [-3,3012+0,9439 ln (D2H)]
References[1] Hawthorne, W., Grut, M., & Abu-Juam, M. (1998). Forest production and biodiversity conservation in Ghana, and proposed international support of biodiversity conservation.
The poor attendance rate of secondary and pioneer species indicates that the
disturbance in this forest has been very limited and is confined to small areas.
The high biodiversity that characterizes Ankasa forest is remarked by the GHI
which resulted in 197, within the sampling area. The percentage distribution of
species according to the index of rarity is shown in Fig. 3
Fig 1 - Measuring LAI by
hemispherical photo technique.
0
1
2
3
4
5
6
7
8
9
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20
LAI
Sub plot
LAI
LAI
Fig 6 - LAI values estimated
in the sub plots along the
transects.
Fig 3 - Star ratings for biodiversity conservation.
•Black: urgent attention to conservation of populations
needed. Rare internationally and not common in Ghana.
•Gold: fairly rare internationally and/or locally.
•Blue: widespread internationally but rare in Ghana, or
vice-versa.
•Scarlet, red and pink: common but under pressure
from exploitation.
•Green: no conservation concern.
•Others: species not yet considered
Biomass
stem diameter [cm]
0 20 40 60 80 100 120 160 180 200
tree
hei
ght [
m]
0
5
10
15
20
25
30
35
40
Error bars: standard deviation
Dashed line: nonlinear regression
Error bars: standard deviation
Dashed line: nonlinear regression
Error bars: standard deviation
Dashed line: nonlinear regression
H = 28,6 *(1-0,97d)
R2 = 0,98