Biome stability and long-term vegetation change in the semi-arid, south-eastern interior of South Africa: A synthesis of repeat photo-monitoring studies

Abstract

We synthesize recent literature concerned with the nature, extent and rate of vegetation change in the Albany thicket, Grassland and Nama-karoo biomes of the semi-arid, south-eastern interior of South Africa at a range of spatial and temporal scales in relation to local and global drivers. The change in cover of three main growth forms (grasses, dwarf shrubs [<1m] and tall shrubs [>1m]) at the community, ecotone and biome levels was analysed using field surveys and repeat photography spanning 27 to >100years. There has been an increase in grass and tall shrub cover and a decrease in dwarf shrub cover across the region over time. Vegetation composition and cover has been most stable in the Albany Thicket biome while Azonal habitats across the region have changed the most. The Grassland biome has experienced a significant increase in the cover of grasses and tall shrubs and a significant decline in cover of dwarf shrubs. Total cover and the cover of grasses have increased significantly in the Nama-karoo biome. We interpret these patterns as evidence for a south westwards shift in the Grassland/Nama-karoo biome boundary in the second half of the 20th century. Although there has been relatively little change in the boundaries between the Albany Thicket and adjacent biomes, several species with subtropical biogeographic affinities have increased in cover and abundance over this period in all biomes investigated. Drivers of the observed changes include rainfall amount and seasonality, temperature, land use and elevated CO2 concentrations in the atmosphere.