An analysis of vegetation cover components in relation to climatic trends along the Botswana Kalahari Transect

Information on soil organic carbon (SOC) and vegetative cover components (e.g. plant litter) in relation to climatic factors along savanna ecosystem moisture gradients is critical to the understanding of ecosystem functioning and should provide insight into vegetation adaptations to climatic change. This work intends providing a synthesis of both vegetative cover components and climatic trends along the Botswana Kalahari Transect (BKT) to indicate the extent to which present day climate might influence the natural vegetation cover. Independent field results of natural vegetation cover components from 57 sites along the BKT showed general increases in both SOC and vegetation cover components along the temperature/moisture gradient. However an anomalous trend towards lower values was identified in the north central Kalahari. This takes the form of declines in density and structural type of woody vegetation cover (and SOC) with increases in shrubs and gasses. Climatic data which are available from synoptic stations offset along the transect show general increases in temperature and rainfall along the BKT but the trends are also characterised by apparently anomalous declines in the north central Kalahari region. The anomaly takes the form of decreased rainfall and increased temperature. In terms of tentative correlation between the two data sets, the highest degree of apparent association takes place between the vegetative components and temperature data. This suggests that while rainfall is obviously significant, temperature variation (including diurnal temperatures) may have a greater effect on the distribution of SOC, woody and live herbaceous cover, than had previously been thought. In terms of plant responses to climatic conditions in the north central Kalahari, this may be explained in terms of soil moisture deficits and concomitant increases in evaporation/ evapotranspiration which has likely contributed to near surface calerete formation over time. Hence both climatic and edaphic factors appear to have been influential in retarding plant growth and limiting species types. Further work is required to explore these relationships along the Kalahari Transect.