Round Trip Flight To Kirstenbosch

An equally important research project at the KRC, undertaken by one of Guy Midgley’s Ph.D. students, Barney Kgope, and co-supervised by UCT ecologist William Bond, was on the responses of savanna trees to increased concentrations of atmospheric carbon dioxide. The rise in atmospheric carbon dioxide is well documented and shows a 25 per cent increase over the past 50 years, forming the basis of suggestions that the globe is facing a seriously accelerated warming event. What Kgope found is intriguing, and of key importance for stock farming and wildlife tourism in the savanna regions of Africa and other intertropical areas (see The fate of Africa’s savannas).

Studies on the responses of savanna trees to increased concentrations of atmospheric carbon dioxide suggest that major changes in the ratios of woody plant to grass in savanna ecosystems could occur in the future.

The grasses of African savannas photosynthesise following what is called the C4 process, which is more water efficient than the more common photosynthesis pathway, called C3, used by temperate grasses, shrubs and trees. Growth rates of C4 plants are only marginally influenced by the concentration of atmospheric carbon dioxide. Trees and shrubs following the C3 process, however, are positively enhanced by increased atmospheric carbon dioxide. Using specially designed growth chambers, Kgope was able to demonstrate a marked increase in growth rate, both of shoots and roots, of savanna trees exposed to the levels of carbon dioxide expected within the next 50 years, if current trends of fossil-fuel use continue. In African savannas, the balance between grasses and trees is maintained by fire. Fires of normal frequency and heat are sufficient to kill most young trees at the sapling stage, resulting in the mosaic of trees and grassy areas typical of the African savanna. But, if saplings grow just a little faster, they can emerge above the kill-zone of fires and grow to maturity – forming a closed woodland, or worse, a dense thicket. Once a tree or shrub canopy is established, the C4 grasses will not receive enough sunlight, their biomass will gradually decrease, fuel loads will reduce and fires will become less frequent. What was originally a productive savanna, providing a mix of grazing and browsing for cattle or wildlife populations, will transform into an unproductive thicket, with serious socioeconomic consequences.

Biodiversity data sets – the building blocks of predictive ecology

‘Not everything that counts can be counted, and not everything that can be counted counts. This somewhat cynical quote is attributed to Albert Einstein (1879-1955). The reality is that predictive ecology demands accurate information on the abundance and distribution of animals and plants. Much of this information on African ecosystems was laid down during two centuries of botanical collecting that preceded modern ecosystem studies. What accelerated our understanding of climate/biodiversity dynamics in South Africa was the establishment of several atlassing projects – a compendium of georeferenced information, where the exact geographic location of the record can be fixed to an accuracy of a few metres through the use of satellite-based geographic positioning systems, or through the use of fine-scale maps. In the case of birds, South Africa has one of the finest information systems available anywhere, based on bird sightings collected by thousands of volunteers over the past 30 years. More recently, other networks have been established, making use of the power of mobile phones, digital cameras and the internet to rapidly document information on butterflies, reptiles, frogs and spiders. Many of these are now incorporated and funded through the wider science network of SANBI.