Adansonia digitata distribution, structure, abundance and elephant damage across Gonarezhou National Park, southeast Zimbabwe.

Abstract

An assessment was made to determine density, structure and distribution of baobabs across Gonarezhou National Park (GNP) management strata, southeast Zimbabwe. The three GNP management strata coincide with a soil group type gradient derived from (i) rhyolite, (ii) malvernia and (iii) granophyre substrates/bedrocks. A total of 225 baobabs were sampled on 15 belt transects of constant width of 0.3km and cumulative total length of 17.2km. The fifteenth baobab point in each belt transect determined the length of a particular belt transect. Abundance was determined from baobab density and frequency. The present study observed that baobab density in GNP ranged from 34.3/km2 in the Central GNP stratum to 69.8/km2 in the Northern GNP stratum. Analysis of variance (P>0.05) showed overall insignificant differences in baobab distribution of basal area, number of stems per plant, plant height and stem density across GNP management strata. The hypothesis that baobabs do not significantly differ in density, structure and distribution across three management strata of GNP was, therefore, accepted. Elephant dung counts and elephant damage levels on baobabs showed no significant differences across study sites (ANOVA: P>0.05), highlighting uniform elephant damage on baobabs across the entire GNP as elephants roam across the park. Some 84.4% baobabs were damaged and some 15.6 % were undamaged, of which 2% were dead. In contrast, the results suggested that baobab density, structure and distribution were significantly different across the GNP soil substrate gradient. Analysis of variance (P>0.05) showed overall significant differences in baobab distribution of plant height and number of stems per plant across the soil substrate gradient. The results highlighted a concern over the unbalanced size class structure distribution of baobabs on malvernia beds plains in GNP, which suggested a recruitment bottleneck. Study sites on granophyre and rhyolite soil substrates/bedrocks were predicted by redundancy analysis (RDA), to be positively correlated and they were of a similar grouping with inversely J-shape size class distribution of baobabs, which indicated viable recruitment and regeneration of baobab population. Overall, GNP did not seem to indicate that baobabs are in danger of extirpation. Baobab extirpation might be the case only on malvernia bed plains in future. The hypothesis that baobabs do not significantly differ in density, structure and distribution across soil substrates in GNP was, therefore, rejected. The present study recommended that protected area management in arid and semi-arid areas should consider (i) formulating clear thresholds of potential concern to allow for the conservation of sensitive woodlands such as Adansonia digitata woodlands and (ii) establishing long-term baobab monitoring programmes for conservation and (iii) management of elephant to attain GNP carrying capacity levels.