IMPACTS OF CLIMATE CHANGE
ON PLANT DIVERSITY IN SOUTH AFRICA

THE FUTURE OF FYNBOS

Two of South Africa's biomes are rated as global plant biodiversity hotspots. We have looked briefly at the Succulent Karoo, but the Fynbos Biome, also found in the winter rainfall region, is probably better known. This biome has an extraordinarily rich flora, with at least 5 600 of the 8 000 plant species being endemic (restricted) to the region.

Although it covers a relatively tiny area of the Earth's surface, Fynbos is so unique in terms of its plant groups that it is recognised as part of one of only six floral kingdoms of the world - the Cape Floral Kingdom.

Human activities like the emission of greenhouse gases threaten to raise temperatures on Earth higher than they have been in the last 1.5-2.5 million years. How might this affect the Fynbos Biome and, indeed, the entire Caps Floral Kingdom?

As in the Succulent Karoo Biome, climate change will seriously threaten the Fynbos Biome over the next 50-100 years. The northern arm of this biome may disappear altogether, and we will lose many of the more drought-sensitive fynbos plants. Because the biome has a very high proportion of endemic species, any loss of range will result in extinctions.

Despite these concerns, the mountainous terrain of much of the Fynbos Biome provides some hope. Within these rugged habitats are many niches where plants can survive. As it gets hotter, plants can also theoretically retreat to higher, cooler altitudes. Furthermore, coastal fynbos may experience less extreme changes in climate, thanks to the moderating effect of the ocean.

Climate change may also cause fynbos plants to go extinct because of a number of secondary effects:

As the climate becomes hotter and drier, fires may become more frequent and extensive. If Fynbos burns before plants are old enough to set seed, local extinctions could result. Drought may also kill adult plants before they can set seed.
Many plants rely upon animals for their survival. Pollination and seed dispersal are two processes aided by a variety of birds, insects and rodents. Climate affects animals and plants in different ways: day length may influence flowering, but temperature may control the life cycles of insects. What could happen if the life cycles of these mutually dependent plants and animals got out of synch? At this stage, our understanding of the physiology of indigenous plants and animals is limited - but we can speculate that climate change could disrupt many of these close and essential relationships.
Climate change may also affect the growth of alien plants in the Fynbos Biome. As the fires on the Cape Peninsula in January 2000 showed, woody aliens are a hazard not only to the fynbos but also to people's property. Increasing levels of carbon dioxide in the atmosphere encourage the growth of woody plants. Could this exacerbate the alien problem in the Fynbos Biome?

Despite these concerns, large tracts of mountain fynbos are conserved and may provide this globally important centre of endemism with a hedge against extinction.
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EFFECTS ON EVOLUTION

In the past, climate change probably had a lot to do with the process of speciation (the evolution of species) which created the plant-rich Fynbos and Succulent Karoo Biomes.

As climates cooled during glacial periods, Fynbos expanded northwards and Succulent Karoo plants took refuge in the Knersvlakte and Richtersveld, both centres of endemism today. As the climate warmed during interglacial periods, the Fynbos retreated into the cooler mountainous areas, and the Succulent Karoo expanded into its current distribution.

These ebbs and flows of plant distribution led to populations of plants becoming fragmented, and then making secondary contact. This provided fertile ground for speciation through genetic changes and hybridisation.
© National Botanical Institute SA
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