Agroforestry has multiple benefits, it's important that they are raised in food security debates so that they can reach their potential.
Agroforestry – the integration of trees and shrubs with crops and livestock systems – has strong potential in addressing problems of food insecurity in developing countries. Done well, it allows producers to make the best use of their land, can boost field crop yields, diversify income, and increase resilience to climate change.
To date, the uptake of agroforestry has been constrained partly because it has lacked a natural 'home' in policy space, but that may be changing thanks to a growing body of evidence of what it can achieve, and how to make it work. The FAO last month published a guide to advancing agroforestry on the policy agenda with case studies of best practice, and is due to hold a conference on forests and food security and nutrition in May.
"In recent years we've seen increasing interest in agroforestry as an important component of sustainable land use and development," says Douglas McGuire, team leader on the FAO's Forest Resources Management team. "The many advantages it offers are being better understood."
Much of that new understanding has come from the FAO itself and from the World Agroforestry Centre (ICRAF), which has built up a body of research on issues such as the use of particular tree varieties and how they can improve soil quality, complement specific field crops, and generate new income streams for smallholders.
For example, one of the major potential benefits of on-farm trees is their ability to replenish nutrient-depleted soil, and the results of a 12-year study by ICRAF published in September 2012 showed how the planting of a particular tree variety – Gliricidia – as a fertiliser tree alongside maize improved the stability of harvests of this staple food crop in sub-Saharan Africa.
The study, based on farming systems in Malawi and Zambia, foundGliricidia to be particularly effective at drawing nitrogen from the air and fixing it in the soil, reducing the need for large doses of manufactured nitrogen fertilisers. The leaves shed by the trees also replenish the soil, increasing its structural stability and capacity to store water.
Another fertiliser tree – Faidherbia, an indigenous African acacia – has also been found to be useful in agroforestry systems thanks partly to its unusual phenology. Faidherbia goes dormant and sheds its nitrogen-rich leaves during the early rainy season, when crops are being planted, and resumes leaf growth in the dry season. That means it fertilises crops at a useful time, but doesn't compete with them for light, nutrients or water.Several studies have found Faidherbia-maize inter-cropping to increase maize yields, by as much as 400% in one area of Malawi.
This doesn't mean that particular tree varieties should necessarily be pushed as "good" for all farming systems; rather, it's important to use the right trees in the right place. "There are often trade-offs involved, and these need to be carefully assessed and balanced, according to the objectives one is trying to achieve," says McGuire. "Soil fertility enhancement, erosion control, food production, wood production, and shading are all factors. Systems where wood production may be a main objective might not be the most favourable to enhancing soil fertility, but that may be an acceptable trade-off under the given circumstances."
Even where certain trees can bring clear benefits, they are often a long-term investment. Resource-poor smallholders can be reluctant to allocate land to trees when it might take years to reap the rewards. But depending on the objectives, certain varieties or planting techniques can speed things up.
"Calliandra and leucaena are two leguminous trees which are known to deliver relatively quick pay offs for use as fodder for livestock," says Frank Place, impact assessment adviser at ICRAF and co-editor of the FAO guide. More
