Enhancement of diversity, stand structure and regeneration of woody species through area exclosure: the case of a mopane woodland in northern Botswana

INTRODUCTION: An area exclosure is the practice of land management that involves the exclusion of livestock and humans from openly accessing an area that is characterized by severe degradation. Area exclosures have been employed as cheap and convenient means of rehabilitating degraded forests/woodlands. A study was carried out to (i) assess the species richness, diversity and evenness; (ii) determine the densities, frequencies, dominance and importance value index; and (iii) assess the population structure and regeneration status of woody species inside and outside the fence (area exclosure) of Okavango Research Institute (ORI) located in Maun, northern Botswana. RESULTS: Thirty-five woody species were recorded inside (32 spp.) and outside (24 spp.) the ORI compound, and the population structure and regeneration status of the woody species were better inside than outside the ORI compound. The exclosure had seven times higher mean density of woody species than outside ORI, and an exceptional regeneration of seedlings was observed inside than outside the ORI compound, suggesting the process of recovery of the degraded woodland. The frequencies of more than half of the woody species also showed increment inside than outside the exclosure. The results suggest that the exclosed area is still in an initial recovery stage since it had been an open grazing area prior to the establishment of the exclosure. Most of the woody species encountered outside ORI showed hampered recruitment and regeneration, owing to different anthropogenic impacts and overgrazing by animals. CONCLUSIONS: Despite the relatively short period (10 years) of exclosure establishment, results from the present study have further provided empirical evidences on the actual crucial roles played by area exclosures to increase woody species richness, diversity, evenness, density, frequency, dominance and important value index as well as enhance the population structure and regeneration of the woody species in northern Botswana. Future research is recommended focusing on comparative studies on herbaceous species richness, diversity and density, horizontal and vertical distribution of soil seed banks, species richness of soil microorganisms, plant and soil biomass, plant and soil carbon pools (above and below ground) as well as soil contents and properties inside and outside the ORI compound.