Sustainable agroforestry to reduce the impacts of climate change (part 1)

Sub-Saharan Africa has seen drastic population growth in the past decade with nearly 50% of the population living in dense urban centres. Such rapid growth puts pressure on agricultural production and thus, land use. Decline in soil fertility and increasing soil erosion are threatening the survival of small scale farming in Africa Additionally, farm production is under threat from climate change, especially the unstable monsoon patterns and the production of livestock fodder. 


What is Agroforestry? 

Agroforestry is the intentional addition of plants and trees in croplands and livestock systems. It is a practice credited in reducing the impacts of climate change on land and providing food and resources to both people and livestock. In recent years, more studies have investigated the benefits of agroforestry in Sub-Saharan Africa to improve soil fertility, prevent soil erosion and produce high quality, year round fodder for livestock while generating income for local communities.  In 2019, a group of NGOs announced they would fund $85 million for a project to enhance agroforestry in Tanzania, Uganda, Malawi, Zambia, Kenya and Ethiopia in what they are calling "the biggest land restoration project ever seen." In addition to encouraging the regeneration of land and conserve biodiversity, the Global EverGreening Alliance hopes this project will capture 20 billion tons of CO2 annually by 2050, which would aid in offsetting the fossil fuel emissions during that same period. Today, agroforestry is estimated to have captured 45 gigatons of carbon and this figure is estimated to grow as more countries adopt agroforestry practices in their farm and crops lands. 

Crops in Sub-Saharan Africa benefiting from the proximity of drought resistant woody plant shrubs. Source: Mongabay

Climate change mitigation

By improving cropping practices and reforesting farms, cultivated lands have a significant potential of reducing the impacts of climate change. Mbow et al, 2014, investigated the prospects of agroforestry in Sub-Saharan Africa in storing carbon. Tree density in farmlands range from a low cover of 5% in regions like the Sahel to more than 45% in tropical ecosystems. In Sub-Saharan Africa, 15% of farms have tree cover of at least 30%, this suggests that there is a high potential that Sub-Saharan Africa could be an important carbon sequester while reducing other agricultural greenhouse gas emissions through increased agroforestry. However, the success of mitigating climate change through agroforestry depends on the tree species selection and the management of such plantation. Furthermore, the soil characteristics, topography, rainfall, and agricultural practices will determine the ability of mitigating climate change through agroforestry. For example, to improve soil fertility, nitrogen fixing trees will be best suited and in order to improve the availability of freshwater, plantations will need to be more dense to reduce evaporation. It is estimated that agroforestry systems have 3-4 times more biomass than treeless farmlands and in Africa they are the third largest carbon sink after primary forest and fallows. An estimated 1550 million hectares are suitable for some type of agroforestry in Africa reflecting that globally, agroforestry systems have a much higher potential than previously believed. 

Overcoming seasonal water limitations 

The benefits of increasing tree cover on farmlands go beyond carbon sequestration as it can help with biodiversity protection, decreased albedo and drainage basin conservation. Agroforestry plays a part in ecosystem functions through water recycling by increased rainfall utilisation compared to traditional farms. Trees help crops with soil moisture uptake through the adaptability of using off-season rainfall and residual water remaining in the soil after the cropping period. Furthermore, there is clear evidence that agroforestry improve water use in farmlands by reducing the loss of water from runoff, evaporation and drainage. In Burkina Faso, Tobella et al, 2016 explored how Shea trees changed their source of water depending on the season. It was discovered that during the wet season, despite having the most water in the soil surface, Shea trees accessed water from slightly deeper soil in order to allow the crops to use the surface water. In contrast, in the dry season, the trees obtain most of their water from groundwater, thus leaving the remaining shallow water to crops. Understanding the symbiotic relationship between trees and crops can give crucial information about water use and how to adapt to the seasonality of precipitation in Africa.

In the next post, I will discuss two case studies. The first being how agroforestry has increased productivity in the Sahel region and the second being soil water competition in South Africa.