Sustainable agroforestry to reduce the impacts of climate change (part 2)
In the previous post, I discussed how agroforestry in Sub-Saharan Africa can help mitigate the effects of climate change through carbon sequestration and water recycling. In this post, I will explore two agroforestry case studies from the Sahel and South Africa.
A typical agroforestry system. Source: Katungulu, 2018
Increasing Productivity in the Sahel
The Sahel is a semi-arid region stretching from Western to Eastern Africa. It is the transition from the Sahara to the North and the humid savannah to the South. Primary production in the region is limited by water availability, especially in the Northern Sahelian zone. Woody trees influence the soil water balance through rainfall interception, evapotranspiration and soil infiltration and runoff. In addition, they provide protection for young crops through windbreak and shading. However, the positive influence of agroforestry on soil fertility and primary production in croplands depends on average annual rainfall and soil type. Woody trees must be chosen with caution due to the limited water supply in the Sahel. In addition, the short supply of phosphorus in the Sahelian soil does limit nitrogen fixation in woody trees and thus nutrient uptake from deep soil is restricted. Introducing agroforestry in the Sahel is thus something that requires careful thought and choices.
Agroforestry practices have been successful in the Sahel especially in aiding with climate stress resilience, water, energy and food security and development opportunities. These achievements help promote sustainable development through functional ecosystems, livelihood opportunities and human security in the region. Successful agroforestry systems in the Sahel are distinguished through "conducive environment at the far level in terms of institutions, management, enhancing the farmer's capacity, and good infrastructure." (Elagib and Al-Saidi, 2020:1).
Agroforestry in the Sahel is important for the security of water especially for soil moisture, runoff and groundwater recharge as vegetation cover plays an important role in affecting local and regional rainfall patterns in the Sahel. The southern Congo rainforest is shown to promote rainfall in central Sudan located in the Eastern Sahel. Thus, forests are key for climate change mitigation in the area as agroforestry systems are 15% more likely to promote storms than treeless farms, which in turns helps to increase primary production in the region.
South Africa
Generally, it is accepted that alley-cropping systems of crops and trees through agroforestry can enhance soil fertility while reducing soil erosion and providing food, fuel and fodder for communities. A study conducted by Everson et al, 2009 analysed the effects of four fodder tree species on soil water and maize production in South Africa. 216 trees were planted in rows 0.75m apart intercropped with maize in a north/south direction to minimise the shading on crops. The main goal of this study was to determine the level of competition between the fodder trees and the crops for soil water in an agroforestry system. The water content of the soil was measured in the upper 0.3m of the soil and the rainfall and seasonal trends were recorded over a four year time period. Between 1996-2001, there were no annual anomalies in rainfall patterns.
Overall, there was no evident competition between the maize and the trees for water. In the dry season, it was apparent that the trees were obtaining their water from deeper soil to leave the upper layer for the maise crops indicating that there was no competition between the plants. This could be explained by the trees having deeper taproots and thus obtaining their water from deeper soil as well as the shading effects trees have on the soil, which reduces evaporation rates and thus leaves higher moisture content for the crops.
Thus, while it can be argued that agroforestry system could only work if trees can have access to deeper soil, it is clear from this study that there is no obvious competition between trees and crop for water. However, the success of agroforestry systems does depend on the type of tree chosen, the quality of the soil and the overall access to water. Furthermore, it was noted that the trees do reduce the amount of light crops receive so it may be important to prune the trees and space them further away from crops.
Conclusion
To conclude, agroforestry systems in semi-arid Africa have an enormous potential in mitigating the impacts of climate change through carbon sequestration and water recycling. In addition, agroforestry has a positive impact on development through the primary production of food and fodder and benefiting the livelihood of local communities. However, successful agroforestry systems are dependent on careful planning, good infrastructure and management.
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