Linking biodiversity to ecosystem function: a challenge to fynbos ecology

In a joint international and interdisciplinary programme, the International Union of Biological Sciences (IUBS), the Scientific Council on Problems of the Environment (SCOPE), and UNESCO have recognized 13 different types of ecosystem which merit investigation in the search for insight into the 'ecosystem function of biodiversity'. One such ecosystem type is the set of terrestrial systems with a mediterranean climate, which includes the fynbos region of the western Cape. The Cape's fynbos region is especially diverse. This mountainous part of South Africa, where the pattern of winter rainfall and warm, dry summers makes it climatically comparable to the Mediterranean Basin, has a geographical extent of 90 000 km super(2), and contains an estimated 8 600 plant, 234 butterfly, 288 bird, and 127 mammal species. What does this staggering wealth of diversity - equivalent to that in some tropical rainforest regions - mean for the ecosystems containing it? And what in turn do those ecosystems mean to people? In fynbos, luckily, there is a reasonable basis for conserving diversity on economic grounds. A number of species have a proven record of commercial value. What is more difficult to assess, however, is the role of diversity in supplying services to human communities. The best-known and most highly prized service of fynbos vegetation is its role in providing a dependable supply of high-quality water. Mountain catchment areas have accordingly been afforded high conservation status, with the knowledge that degraded systems, such as those invaded by exotic plant species, can yield up to 50% less water than natural fynbos vegetation. But is the indigenous diversity of fynbos a critical part of the equation? Or would half a dozen well-selected species provide just as good a functional cover for catchments? Ecologists have not yet developed the quantitative insights into links between diversity and the mechanics of natural systems that can provide definitive answers to these practical questions. In the mean time a fine balance of precaution, pragmatism and guidance by current ecological knowledge, will be needed for developments which threaten biodiversity.