Synergies and trade-offs amongst multiple functions of trees in agricultural landscapeswca2014-2461 Shem Kuyah 1 2,*Ingrid Öborn 1 3,Anders Malmer 3,Edmundo Barrios 1,A S. Dahlin 3,Mattias Jonsson 3,Catherine Muthuri 1 2,Sara Namirembe 4,John Nyaga 1,Ylva Nyberg 3,Fergus L. Sinclair 1 1World Agroforestry Centre, 2Jomo Kenyatta University of Agriculture and Technology (JKUAT), Nairobi, Kenya, 3Swedish University of Agricultural Sciences (SLU), uppsala, Sweden, 4Swedish University of Agricultural Sciences (SLU), uppsala, Kenya
There has been a recent surge of interest in multifunctional landscapes within an agroforestry context but little formal assessment of the roles that trees play across the spectrum of ecosystem service provision now considered important in sub-Saharan Africa. We reviewed functions of trees in fields, on farms and in agricultural landscapes across contrasting landscapes in SSA to assess the scientific evidence base about their impact on ecosystem service provision. Data was gathered primarily from peer reviewed journal articles dating from 1995 to 2013, selected using a combination of electronic and manual literature searches. This resulted in 324 articles relevant to arid (3%), semi-arid (50%), sub-humid (25%) and humid (22%) agro-ecological zones. The articles referred to 184 sites across SSA. The majority of studies were from West and Central Africa (42%), followed by eastern (37%) and southern Africa (21%); of which 25, 66 and 45% of the regions’ studies were conducted in Nigeria, Kenya and Malawi, respectively. The functions of trees were grouped into four major ecosystem service classes from the millennium ecosystem assessment: (1), provisioning, (2) supporting (3) regulating and (4) cultural. The review shows that trees influence provision of food, fodder, fuel, timber and non-timber products; they support biological nitrogen fixation, nutrient cycling, primary production, soil fertility and water cycling; and regulate agro-biodiversity, carbon sequestration, genetic resources, microclimate, pests and diseases, soil erosion, weeds and wind speed either positively or negatively and to varying extent depending upon tree species, site and management. Food production, nutrient cycling, primary productivity and soil fertility are the foremost functions explored, contributing over 60% of the studies. Trade-offs and synergies amongst ecosystem functions of trees are evident across scales and it is clear that they often play a vital role in sustaining productivity gains from agricultural improvement, through tightening nutrient, water and carbon cycles.