Abstract:
Anthropogenic disturbances (cultivation, harvesting of poles and firewood and protection) play a
pivotal role in the recovery and growth of Baikiaea-Guibourtia-Pterocarpus woodland species. The aim
of this study is to determine the reliability of tree growth rings in age determination and average radial
growth of re-growing woodland stands. The relationship between stem diameter, number of growth
rings, and age of selected stands was also investigated. The research assisted in understanding the
growth patterns of the key commercial timber species (Baikiaea plurijuga, Guibourtia coleosperma and
Pterocarpus angolensis) of the seasonally dry Baikiaea-Guibourtia-Pterocarpus woodlands around
Gwaai and Tsholotsho in north-western Zimbabwe. Tree rings were physically counted on basal stem
cross-sections collected from 20 trees of different age, for each species in each disturbance regime.
STATISTICA statistical package version 7.0 (StaSoft inc, 1984 - 2006) was used for data analysis. The
Simple Regression Model was used to test for relationships. The relationship between age and growth
rings, showed a strong correlation (p<0.0001). Diameter and number of growth rings had a poor
correlation. This showed that growth rings and not diameter can be used to determine the age of the
three key timber species. Mean annual ring width was significantly different between species within the
same disturbance category (p<0.005) within a specific stand age. Mean radial growth was highest in
abandoned crop fields, compared to pole and firewood collection sites. It was therefore concluded that
forest managers need to adopt disturbance regimes that prompt optimal mean radial growth of at least
key species in the woodlands.
