Restoring the Soil - Canadian Foodgrains Bank

Decision Tree Guide41Native trees and exotic trees can both be used to provide dispersed shade. A combinationwill provide a wider variety of trees and increase biodiversity, and willtherefore be a more sustainable option. If the farmers select native tree species, goto #25.25. Dispersed shade with native species. The species you decide to use will probablydepend on what is locally available. If a lot of trees already exist in the fields,you can pick and choose among those species, selecting leguminous trees withoutspines, if possible. Though it does have the problem of thorns, Faidherbia albida(previously Acacia albida) is easily the most desirable in very drought proneareas like the northern Sahel because it drops its leaves during the rainy seasonand therefore does not need to be pruned. (Other trees will need some pruningimmediately before the rainy season to reduce crop shading.) Furthermore,because it is dormant during the rainy season, it does not compete with nearbycrops for water. Therefore, despite its thorns, F. albida is preferred by farmers innorthern Sahel. Nevertheless, as one moves from the drier areas to higher rainfallregions, the advantages of the F. albida will diminish in importance, and theproblems of its thorns and relatively slow growth will make it less desirable thansome other species.Trees like the shea butter trees that produce an income are also a desirable option.Those wanting to use native species in dispersed shade systems in very dry areas(such as the northern Sahel) should consider using the Farmer Managed NaturalRegeneration (FMNR) system. In this system, instead of establishing nurseriesand planting trees (a process that in these extremely difficult environments failsmore often than it succeeds), farmers are encouraged to quit cutting or burning,and to protect the trees that grow naturally each year from stumps or undergroundroots in their fields. In many of these environments, well over 50 suchstumps or roots per ha already exist. Trees grown this way almost always survive,and often grow much faster than trees grown from seeds because the new trees donot have to grow a new root system. On the other hand, farmers have to resignthemselves to having trees of various species growing in their fields in a randomspacing. In Mali, many Dogon farmers prune these trees in order to maximizecrop production under the trees, and some plant additional trees by feedingviable seeds of desired species to their cattle. FMNR has been used to successfullypopulate hundreds of thousands of hectares of cropland with trees in Mali,Burkina Faso and southern Niger.26. Dispersed shade with exotic species. First, remember that having many differentspecies in your field (that is, having high biodiversity) is always good. If youcan combine some native trees with the exotic trees, the system will be less riskyand perhaps more sustainable—because if one tree species dies out, others canstill be used. It should be noted that most native trees grow much more slowlythan leucaena or mother of cacao.