The effect of catena position and stump characteristics on the coppice response of three savannah fuelwood species

Abstract

Fuelwood is still the primary energy source for rural households across the savannah biome of Africa. Coppice growth is an important species-specific trait that strongly influences fuelwood production and regeneration, and yet coppice growth patterns are poorly understood in African savannahs. It is therefore vital that factors affecting coppice growth of species, such as environment conditions and harvesting technique, be better understood in order to develop models for sustainable fuelwood use. This study investigated coppice growth and resource allocation strategies in relation to (1) position along the landscape catena and (2) harvesting technique, for three savannah fuelwood tree species: Dichrostachys cinerea, Albizia harveyi and Combretum collinum. The study was conducted in a dystrophic semi-arid savannah in the far north-east of South Africa. A total of 1146 harvested stumps were sampled in topland and bottomland sites in three locations around a rural village. Stump characteristics (diameter and height) and coppice shoot variables (number of shoots, length and diameter of each shoot, length of longest shoot, and diameter of fattest shoot) were measured for each stump. Three soil samples were taken in each site for physical and chemical analysis. No statistically significant differences were found in soil variables between topland and bottomland sites, probably due to low sample size. Coppice resource allocation strategies varied between species. D. cinerea exhibited a ‘quantity-driven’ strategy, with the production of large numbers of relatively small coppice shoots with high length:diameter ratio (shoot taper function). C. collinum exhibited a ‘quality-driven’ strategy, characterized by the production of a relatively low number of larger coppice shoots. Coppice growth variables for A. harveyi were intermediate between those of the other two species, suggesting a strategy where allocation of resources to the number and growth of shoots is more balanced. However, allocation of resources relative to the size of the cut stem, indexed by total shoot basal area:stump basal area ratio, did not differ significantly between species. Coppice growth was strongly favoured in bottomland sites for D. cinerea, and to a lesser degree, C. collinum. Catenal position had a negligible influence on coppice growth of A. harveyi. Number of shoots produced increased with cutting height for all three species. For all three species the number of shoots increased with stump diameter, and mean shoot size also increased with stump size for D. cinerea. There was a significant negative relationship between stump diameter and total shoot basal area:stump basal area ratio for A. harveyi and C. collinum. A framework for optimizing different coppice growth variables according to species, catenal position and harvesting technique is given.