Miombo agroforestry economically and ecologically viable
Models of agroecosystems are usually designed as if they are dead, according to David Storey, who will graduate with a MSc in Ecological Agriculture at the end of this month. Trying to make a model of a living system, one which is both ecologically and economically viable, was the research challenge undertaken by Storey in the southern highlands of Tanzania. Dead systems are those which are very oversimplified, based on predictability models that cannot reflect the various interactions involved in a natural system. In typical agroforestry projects, for instance, trees are planted in lines, to be harvested after three years, with no natural regeneration or room for different stages of growth. Storey's design aims to mimic the living development processes and interactions found in a natural forest
Working on community forestry projects in Tanzania for three and a half years, Storey noticed how unsuccessful the projects were. Exotic species like Eucalyptus, Leucaena and Pine were given for free to the community, to be planted in woodlots. But these trees were not necessarily appropriate to the arid soils, and ended up being decimated by termites. Storey argues that it is much better to use species which are indigenous to the region. 225225Only in the last five years have Miombo forests been acknowledged as containing useful trees. Because of their small size, these trees fall below the official quantifiably productive cut-off point of a 15 cm diameter. Miombo forests cover 270 million ha in Southern Africa and are becoming more common in forestry research because of their many beneficial qualities. Miombo trees are mostly deciduous legumes, so provide a dependable source of nitrogen. Making a mulch of the leaves can release as much if not more nitrogen than manure which is usually collected once a year from the corral. Also, buying manure to supplement the nutrients is ten times more expensive than if farmers collect the leaves for mulch. Miombo foliage also provides a very good source of fodder for cattle and the trees have a remarkable capacity for regeneration.
Storey proposes an agroforestry system with minimal external inputs, which integrates crop and livestock systems into the already existing Miombo forest. His design is based on an analysis of the Miombo trees along a 4x50 m transect typical of the vegetation on existing farms, and keeps within the socio-economic restrictions of an average farmer in the region. His model should allow farm economic profits to rise from the present US 255 to about US 730 per year. Am.S