Ecosystem services must be preserved in Sahelian parklands
The sustainability of agroforestry parklands in the Sahelian zone of West Africa is under threat from an increasing population and climate change. To improve production, greater research – combined with local knowledge – is needed on the ecosystem services provided by the parklands.
“Trees in the parklands provide important services, such as the provision of food and livestock fodder, as well as create microclimates that can be favourable for production and increase the carbon content of soils,” outlines Jules Bayala, Senior Scientist in Ecophysiology with the World Agroforestry Centre and lead author of a new article in Current Opinion in Environmental Sustainability which provides a synthesis of ecosystem functions that occur as a result of the interactions between various components in the parklands.
Bayala and colleagues compiled data on parkland practices from a wide range of sources, including research projects, replicated experiments and observational studies. In their synthesis, they look specifically at the effects of parkland systems on food production and climate change in the Sahel.
The scientists found that trees in the parklands have an important role in a range of ecosystem services, including: provisioning services (such as food and fodder), regulating services (such as climate and water availability), and supporting services (such as nutrient cycling).
“Any measures to increase and diversify production in the parklands must ensure these important services are preserved or enhanced,” stresses Bayala.
In the agroforestry parklands of the Sahel, generations of farmers have grown crops and raised livestock in fields scattered with trees. The trees are primarily remnants from original natural woodland, and while in some parklands a single tree species may dominate, in others a mixture of tree species and shrubs can be found.
“The parkland trees are an important source of firewood, medicine, food and in some cases income,” explains Bayala. “They also help to reduce erosion and provide fodder and shade for livestock.”
In managing the parklands, farmers rely on their ecological knowledge of the system in order to make decisions that minimise risks associated with variations in climate. Typically they plant staple cereal crops (millet, sorghum and maize) together with legumes such as cowpea or rotated with groundnut. Livestock feed on crop residues and the leaves and pods of fodder tree species while also depositing manure in fields which aids nutrient recycling.
“The complex interactions between trees, crops and livestock affect the way in which ecosystem services in the agroforestry parklands function in several ways.”
For example, while trees may actually have a slightly negative effect on cereal yields (due to competition for light, nutrients and water), they provide an essential provisioning service as a source of edible products for nutrition and in providing high quality livestock fodder that is particularly important during the dry season and droughts.
Trees also help to regulate climate and water availability. The scientists found that crops grown under certain trees are less exposed to excessive temperatures and less affected by wind. Soils under trees may hold more water or change the way in which water is redistributed from deeper to shallower layers of soil. This latter function may be an important mechanism to reduce drought stress whereby particular trees can access deeper water.
The scientists also point out that trees in the parklands can have some negative effects relating to climate and water. The microclimate under trees can be more humid leading to greater disease such as fungal attack. There can also be reduced water under trees as a result of dense canopy cover.
Perhaps the most important supporting service offered by trees is that of preserving and sustaining favourable soil conditions for the production of staple crops. Trees help to increase carbon storage which is important for soil fertility. If leaf litter fall and decomposition is combined with leguminous species, the soil has higher nitrogen content. Birds and other animals depositing faeces under trees can also help to improve soil fertility.
“There is an argument that trees may not actually contribute to soil fertility but merely redistribute it,” says Bayala. “In any case, trees maintain fertility, and without them fertility would be rapidly depleted.”
Bayala and colleagues believe there is a need for more comprehensive analysis of the multiple benefits and services provided by parkland trees. They stress the importance of applying scientific understanding to improve farming livelihoods in low-productivity areas of the Sahel.
Download the full article:
Bayala J, Sanou J, Teklehaimanot Z, Kalinganire Z and Ouédraogo SJ (2013) Parklands for buffering climate risk and sustaining agricultural production in the Sahel of West Africa. Current Opinion in Environmental Sustainability 6: 28–34.
This article appears in a special issue of the journal Current Opinion in Environmental Sustainability on the theme ‘Sustainability challenges.’ The full special issue is available Open Access at http://www.sciencedirect.com/science/journal/18773435/6/supp/C
The issue will be launched during the World Congress on Agroforestry in Delhi, India in February2014.