Shoot Biomass of Natural Stump Regrowth in Cropping Systems in the Subhumid Forest Savanna Mosaic Zone of West Africa.

Abstract

A rapidly growing population calls for intensified cropping in the region, endangering the ecological and economic success of traditional bush fallowing which depends on a site specific balance of crop and fallow components in space and time. Research has hence given trees and shrubs a key role in ecosystem conservation as well as in increasing crop yields, yet the contribution of naturally occurring stumps to shoot biomass turn-over in farmers' fields has not been evaluated with respect to its agroforestry potential. The regrowth and productivity of natural stump species was therefore studied in different cropping systems and environments in southern Bénin in and compared to exotic agroforestry trees. In fields where negative impacts of land-use on natural vegetation, such as burning and weeding, was still moderate, 32 stump species with densities of 0.0315 m_2 were recorded contributing a total of 14.2 g m_2 shoot dry matter after 285 days of regrowth. By renouncing burning and selective weeding, number of stump species increased to 36 in the subsequent year, producing 98.8 g m_2 total shoot dry matter at densities of 0.086 individuals m_2. In particular, species of the mature forest such as Albizia species, Baphia nitida, Lecaniodiscus cupanoides, Morinda lucida, and Rauvolfia vomitoria responded favorably to protection, contributing not only significant amounts to shoot biomass turnover, but also being much more efficient in accumulating biomass than exotic agroforestry species such as Gliricidia sepium. Neither NPK fertilization nor planting of fast growing exotic tree species influenced natural stump growth and productivity in any significant way. The preservation and management of natural stumps between crops represents therefore an economic agroforestry option worth consideration in the future. This would simultaneously help to conserve the multiple products and services of these stump species to man as well as preserve the functioning of the natural ecosystem in the region.