Vanishing Multipurpose Indigenous Trees in Chobe and Kasane Forest Reserves of Botswana

The continued threat to the forest and land resources has been acknowledged in many parts of Botswana. In 2003, a field study was carried out to assess the structure and composition of Chobe and Kasane Forest Reserves. In both forest reserves ten plots (25 m x 25 m) were established at 100 m inter-plot spacing along a transect of 1 km. The information recorded from each sample plot includes tree and shrub species name (species identification), diameter at breast height (dbh) and height of all trees with at least 3-cm and indicators of biotic disturbances/human and animal disturbances (stems cut, dead and wounded trees, grazing/browsing, burnt areas). The forest structure was described by species diameter class distribution, basal area and species diversity index (Shannon's Index) while the number of different species described the forest composition. Chobe Forest Reserve showed the highest number of total stems per hectare/tree density (2048 stems/ha) as compared with Kasane Forest Reserve (544 stems/ha) with most of the trees being found in the 21-30 cm (672-stem ha -1 ) and 41-50 cm (144-stem ha -1 ) diameter classes respectively. Chobe showed significantly (P = 0.05) higher tree basal area (146.20 m 2 ha -1 ) and species diversity (H: 7.7281) as compared with Kasane (i.e. basal area: 41.93 m 2 ha -1 and H: 6.7038). The average tree mortality rate in Chobe was 60% with Pterocarpus angolensis showing the highest proportion (21% tree losses). Out of the 40% living trees, however, fire or elephants either wounded 16.3%. Kasane showed higher proportion of wounded living trees (26.5%) as compared to Chobe. It is concluded that Pterocarpus angolensis (Mukwa), Baikiaea plurijuga (Mukusi) , Combretum zeyheri , Combretum gratissimus, Terminalia sericea (Mogonono) , Burkea africana ( Monalo /Musheshe) and Lonchocarpus capassa dominate the vegetation of Chobe and Kasane Forest Reserves. Chobe Forest Reserve, however, is high diverse in terms of species and more stable as compared with Kasane Forest Reserve. Abundance of young trees in Chobe Forest Reserve provides an indication that regeneration in the forest reserve was taking place and also that the plant population structure is stable. Human activities (eg. illegal and selective harvesting of valuable species) and plant damage by other biotic factors are responsible for the observed losses of valuable indigenous species such as Pterocarpus angolensis , increased land degradation and suppressions of natural regenerations. To reduce the risk of damage from future biotic and abiotic disturbances on Botswana's forest resources, therefore, there is a need for harmonizing societal needs, resource potential and institutions guiding resource use, effective and sustainable forest management, forest conservation and enhancement of forest carbon stocks. More detailed studies, however, are required to determine the species richness (relative density), abundance (relative dominance), importance value index, diversity, volume distribution and canopy cover of all Botswana forests. Qualitative and quantitative data on the destructive impacts of biotic and abiotic disturbances are also urgently needed. Fire management plan and policy also need to be developed.