Changes in abundance and distribution of Protea caffra in the central and northern Drakensberg as a consequence of climate and land use change

Bachelor Thesis


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University of Cape Town

The study investigated changes in populations of Protea caffra at five sites in the central and northern regions of the uKhlahlamba Drakensberg Park, a UNESCO world heritage site. Based on an archaeological study in 1994 that used charcoal remains to compare the size of Protea species populations in the Drakensberg to a much earlier era (between 1260 to 1880 BP), it was hypothesized that there would be a further decline in the number of individuals. A total of 76 historical photographs (dated from 1950-1995) were re-photographed in 2014 and the number of individual P. caffra plants in the two sets of photographs counted to assess the extent and rate of population change. The landform units were demarcated on each photograph according to their catenal position, aspect, elevation and the extent of rocky cover. Geological parameters for each landform unit were obtained from GoogleEarth, climatic data from the South African Atlas of Climatology and Agrohydrology and fire data from MODIS. In 76% of the landform units there was an increase in the number of individuals over time, in 17% a decrease and in 7% there was no change over time. Several hypotheses were generated from a conceptual model based on ecological insight into the study area to explain change in the abundance and distribution of P. caffra. Using an Akaike test, the input models were ranked according to how representative the explanatory variables were of the observed change. The model with aspect and elevation as explanatory variables was ranked the best predictor of change. A greater proportion of increase in the size of the population was found on lower slopes. With increasing atmospheric CO2, P. caffra on the warmer lower slopes are likely to have increased photosynthetic rates and increased productivity. A greater proportion of landform units showing a decrease in P. caffra was shown at higher elevations. The reason could be higher fire intensity at higher elevations. The variation in change influenced by fire suggests it is an important regulator of P. caffra numbers. The fact that there is no relationship between fire frequency and landform units showing an increase in P. caffra implies that the majority increase in the species is more likely to be driven by climatic changes, i.e. increases in atmospheric CO2 rather than a change in the fire regime. Increasing atmospheric CO2 levels lead to enhanced growth rates, postburn recovery and resprouting of tree species in grasslands and savannas, which could account for the majority increase in P. caffra populations in the grassland of the Drakensberg. This has important conservation management implications for the reserve, in that the current fire regimes do not appear to be having a negative impact on the abundance in P. caffra. Further, fire will continue to be an important management tool in maintaining the vegetation structure and grasstree codominance in the reserve.

Includes bibliographical references.