A synthesis of local agro-ecological knowledge on drivers of tree cover change in the Blue Nile Basin: opportunities and constraints to

integrating trees in Diga, Fogera and Jeldu Woredas in Ethiopia.

IntroductionThe quantity and position of trees in a landscape can have significant impacts on farm soil and water resources. Strategic placement of trees can also help mitigate against issues in watershed management. Here we present a synthesis of local knowledge studies conducted in three micro-catchments of the Blue Nile Basin (Diga, Fogera and Jeldu Woredas) exploring natural and anthropogenic drivers of tree cover change as understood by farmers and local experts. This approach can help to better design interventions and gain important historical context within a data sparse environment.

The Diga lowlands provides a clear example of the mechanisms by which deforestation has led to increased erosion, increased fertility loss, increased soil deposition (which has dried the headwaters of streams), decreased rainfall and decreased water quality (Figure 1).

The farmers interviewed demonstrated detailed agro-ecological knowledge on how the physical attributes of trees impact on water and soil resources. Farmers were able to identify tree species which ameliorate the effects of a wide range of environmental degradation issues (Table 1). The tree species known to fulfil these functions were mostly seen at low frequency in the sites, or known to be extinct from the area. Local knowledge on these trees’ regulating services, as well as their utilities has been retained, however, there were found to be knowledge gaps on how to integrate native trees into the cereal and horticultural cropping systems and manage them to reduce competition. Diga was the only research site with well established agroforestry practices, with coffee intercropped with remnant forest species.

Environmental degradation Diga Jeldu FogeraSoil erosion Croton macrostachyus,

Myrica salicifolia, Vernonia amygdalina

Hagenia abyssinica, Ekebergia capensis, Celtis africana

Adhatoda schimperiana, Sesbania sesban

Groundwater decline Syzygium guineense, Albizia schimperiana, Cordia africana

Ekebergia capensis, Ficus spp., Dombeya torrida, Strychnos spinosa

Syzygium guineense, Ficus spp.

Soil fertility loss Erythrina abyssinica, Hagenia abyssinica, Polyscias fulva, Vernonia amygdalina

Hagenia abyssinica, Dombeya torrida, Nuxia congesta

Croton macrostachyus, Cordia africana

Waterlogging Eucalyptus spp. Eucalyptus spp. Acacia spp., Eucalyptus spp.Biodiversity loss Albizia schimperiana,

Ekebergia capensis, Combretum collinum, Prunus africana

Sapium ellipticum, Olea europaea ssp. africana, Nuxia congesta

Otostegia integrifolia, Olea europaea ssp. africana, Combretum molle

MethodsLocal knowledge about drivers of tree cover change was elicited using knowledge-based systems methods (Sinclair and Walker, 1998; Walker and Sinclair, 1998). The knowledge was recorded using the AKT5 software. Detailed knowledge was acquired by repeated semi-structured interviews with a purposive sample of 116 willing and knowledgeable people and focus group discussions were held in three of the NBDC Nile 2 project sites (Plates 1-3). Stratification was based on age, wealth, gender and location. Participatory mapping, historical timelines and transect walks were used to complement interviews. The majority of the knowledge was from men.

Results and discussionLocal knowledge revealed that all three sites suffered from rapid deforestation of native tree cover over the last 40 years. All three systems were recognised by farmers as declining in agricultural productivity. The decline of native forest in Jeldu was found to be more rapid than the other two sites, partially due to market pressures from the capital city. Fogera and Diga were found to have remnant native forest still present, although certain tree species had disappeared completely due to over-exploitation for their products. This was associated with population expansion which has driven land cultivation into more marginal land (such as steeper slopes and marshy lowlands), resulting in land degradation and heightened pressure on common grazing land.

ConclusionsThe results suggest that farmers in all three sites had a significant understanding of interactions between trees, soil and water. Although farmers understood the various functions of trees in watershed management according to on-farm niches and ecosystem service provisioning, there was still a critical gap in understanding the logistics of integrating them at a higher frequency into the current agricultural systems. Such gaps in knowledge should be addressed through technical training and awareness raising. In order to fulfil project goals of improving watershed management in the Blue Nile Basin, farmers’ knowledge about native trees needs to be taken into account when designing tree interventions and promotion of agroforestry species by local government nurseries.

Plate 1: Landscape in Diga, showing trees scattered across the farming landscape. Photograph taken by Genevieve Lamond, ICRAF/Bangor University. July 2011. Plate 2: Landscape in Jeldu, showing cultivation on steep slopes and eucalyptus woodlots. Photograph taken by Martha Cronin, ICRAF. April 2013.

Figure 1: Local knowledge about drivers of tree cover change in Diga lowlands. Nodes represent human actions (boxes with rounded corners), natural processes (ovals), or attributes of objects, processes or actions (boxes with straight edges. Arrows connecting nodes show the direction of causal influence. The first small arrow on a link indicates either an increase ( ) or decrease ( ) in the causal node, and the second refers to the effect node. Numbers between small arrows indicate whether the relationship is two-way (2), in which case an increase in A causing a decrease in B also implies that a decrease in A would cause an increase B, or one-way (1), where this reversibility does not apply.

Plate 3: Landscape in Fogera, showing tree composition on farms. Photograph taken by Fabien Balaguer, Bangor University. July 2011.

Table 1: A sample of environmental degradation issues faced in each of the sites and the tree species known by farmers to ameliorate the effects but were in low numbers across research sites.

Martha Cronina (m.cronin@cgiar.org), Genevieve Lamondb, Fabien Balaguerb, Flavia Venturinib, Tesfaye Sidaa, Tim Pagellab and Fergus Sinclaira,b

a World Agroforestry Centre (ICRAF), Kenya, b School of the Environment, Natural Resources and Geography, Bangor University, UK

ReferencesSinclair, F. L. and Walker, D. H. 1998. “Acquiring qualitative knowledge about complex agroecosystems. Part 1: Representation as natural language”. Agricultural systems 56, pp. 341-363.Walker, D.H. and Sinclair, F. L. 1998. “Acquiring qualitative knowledge about complex agroecosystems. Part 2: Formal representation”. Agricultural systems 56, pp. 365-386.