Woody plant assemblage and the structure of miombo woodland along a disturbance gradient in Hurungwe, Zambezi Valley, Zimbabwe

Abstract

Miombo woodlands near human settlements are under significant pressures from human activities, with negative consequences on their structure and composition. As studies are limited, we assessed the structure and species composition of a portion of miombo woodland along an increasing disturbance gradient from a national park, through a buffer zone to communal lands in northeast Zimbabwe. Five concentric plots of 2 and 11 m radii were established in each area to record woody species composition, diameter, height, basal area, density and volume as well as evidence of disturbance. Effects of site, growth stage and their interaction on vegetation diversity and structural parameters were tested using a general linear model (GLM). Principal component analysis (PCA) tested the association between species and site and ANOVA the differences in the level of disturbance across strata. Species diversity did not differ between sites except for evenness, which increased with disturbance. Evenness and richness were greater in seedlings and saplings than mature trees across sites, respectively. Sapling and mature tree diameters differed significantly between sites. Volume and density of mature trees declined with increasing disturbance while seedling densities peaked at intermediate disturbance levels (buffer zone). Tree harvesting, was more evident in the buffer zone and in the communal area relative to the national park. In contrast, fire frequency was greater in the national park and in the buffer zone relative to the communal area. The results of this study identify a true miombo woodland dominated by Brachystegia boehmii with a stable population, as illustrated by an inverse-J shape in diameter class distribution on all sites, and that these woodlands are generally resilient to disturbances, maintaining similar species composition and structure at various levels of disturbance. However, continued monitoring of disturbance levels and miombo woodland response is recommended to ensure sustainable utilisation of these resources.

Keywords

Miombo woodlands / cComposition / Diversity / Structure / Anthropogenic disturbances

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