WOOD BIOMASS ESTIMATION IN DRY MIOMBO WOODLAND IN ZIMBABWE

This paper is concerned with the wood yield of two of the most common indigenous tree species of Zimbabwean miombo woodland, Brachystegia spiciformis and Julbernardia globiflora. Simple wood yield models were calculated for each of the two species in regenerating dry miombo woodland in central Zimbabwe, in an area which receives a mean annual rainfall of 766 mm. The data were analysed at two levels: initially each stem was treated as an individual, and then stems were combined in coppice stools. The two species were analysed separately at first. Total dry wood biomass was measured in kilograms and stem volume was estimated using stem diameter (d) at 30 cm above ground, stem length (L) (as opposed to tree height) or a combination of both. All data were transformed using the log10 transformation. The best yield model, accounting for 0.98 of the variation for both species, proved to be one using SIGMA (d2L) as the independent variable. A second model, using the diameter of the largest stem in the coppice stool, also gave good r2 values and in view of the time needed to measure all the stems in each coppice stool, this model was considered to be most useful in developing biomass tables. The functions developed for each species separately were not significantly different and therefore the data were combined to produce one model for both species.