Effects of harvesting systems on tree species composition, recruitment, and population structure in Mtangatanga forest reserve, Mzimba District, Malawi.

Abstract

Forests and woodlands are among the most biodiverse and productive terrestrial ecosystems especially in tropics, yet they continue to face extensive degradation driven by unsustainable management. Harvesting systems strongly influence population structure, tree species composition, and recruitment dynamics. The removal of trees alters stand density and may subsequently modify species diversity and forest structure. In Mtangatanga Forest Reserve, both non-selective and unregulated harvesting are practiced with the latter often resulting from non-compliance in areas designated for strict conservation. Selective harvesting and clearcutting are mostly associated with the removal of immature and protected species, potentially undermining forest regeneration. This study evaluated the effects of selective and an unregulated harvesting system practised in Mtangatanga Forest Reserve on species composition, recruitment, and population structure. Twenty concentric nested circular sample plots (ten per harvesting type) were purposively established. Each plot comprised three nested subplots with a radii of 6m, 12m, and 20m, where all trees were identified, enumerated, and measured for diameter at breast height. A total of 644 individual tree species were enumerated, representing 25 species in selectively harvested and 19 in unregulated harvesting areas. Dominant species were in the family of Brachystegia, Julbernardia, and Uapaca. Recruitment, there was no statistically significant difference between unregulated and selective with p > 0.05 in seedling, saplings, and poles. Diversity (Shannon-Wiener index) was significantly higher in selectively harvested areas (H′ = 2.65) than in unregulated areas (H′ = 2.34). There was a significant difference (p < 0.001) with selective harvesting exhibiting a smooth reverse J-shaped size-class distribution, indicating stable recruitment, while unregulated harvesting showed a slightly disturbed pattern. The study concludes that regeneration is sufficient in selectively harvested areas but inadequate under unregulated harvesting. Strengthened forest law enforcement and sustainable management interventions are therefore, recommended to support long-term forest resilience to promote forest-based enterprises.