This document synthesizes local agro-ecological knowledge regarding tree cover changes in the Blue Nile basin of Ethiopia, specifically focusing on Diga, Fogera, and Jeldu woredas. It highlights the impacts of deforestation on soil and water resources, while demonstrating farmers' awareness of specific tree species that can combat environmental degradation. The findings emphasize a critical gap in understanding how to integrate native trees into current agricultural systems, suggesting the need for technical training and awareness to improve watershed management.

1. 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.
Introduction
The 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 Fogera
Soil 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
Methods
Local 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 discussion
Local 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.
Conclusions
The 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
References
Sinclair, 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.