Disturbance impacts on the persistence niche of key species in the Baikiaea–Guibourtia–Pterocarpus woodlands of north-western Zimbabwe

The persistence niche (studied through different modes regeneration) of three key species (Baikiaea plurijuga (Harms), Guibourtia coleosperma (Benth.) J. Leonard and Pterocarpus angolensis) (DC) under five different disturbance regimes (eight years after cessation of disturbance) was studied in the Baikiaea–Guibourtia–Pterocarpus woodlands of north-western Zimbabwe. The disturbance regimes were: protected area (no disturbance); timber concession area (timber harvesting); pole and firewood harvesting sites; abandoned crop fields (after clearing for agriculture); and burnt sites (fire disturbance). Influence of stump diameter and height on regeneration factors was investigated. For each disturbance regime, six main plots (100 m × 100 m) each were systematically laid out (20 m apart) to assess regeneration. In each main plot, 10 m wide transects (5 m apart) were surveyed for seedlings and saplings of the target species (at least 100 plants of each species), resulting in 7 transects per main plot, 42 transects in each study site and 210 transects in total. Number of seedlings with or without a rootstock (i.e., just grown from seed) was recorded. Diameter of stumps was measured at the cut surface. Shoot height was measured from their origin. Each target species was associated with mode of regeneration (χ² = 27 642, P < 0.001). Most plants regenerated from root suckers. Regeneration mode is dependent on disturbance regime (B. plurijuga χ² = 225.66, p < 0.001; G. coleosperma χ² = 158.62, p < 0.001; and P. angolensis χ² = 144.01, p < 0.001). Stump diameter negatively influenced number of sprouts for B. plurijuga and P. angolensis, but positively influenced sprout height for all species. Stump height positively influenced sprout height for G. coleosperma and P. angolensis. The study therefore concludes that disturbances are necessary in facilitating sprouting and growth of suppressed shoots. Stump height and diameter influence the ability of stumps to regrow vegetatively through sprouting. Weak relationships between stump diameter/height and coppice density and shoot height suggest that there are other factors that affect vegetative regrowth through coppicing.