Historical vegetation–environment patterns for assessing the impact of climatic change in the mountains of Lesotho

Abstract

Climate change will probably profoundly impact the Maloti Mountains in Lesotho, which are likely to have a warmer, wetter and more CO₂-enriched (eCO₂) atmosphere in the future. Intensive smallstock grazing could exacerbate the effects of climate change on the mountain grasslands. Vegetation composition data collected in ca. 1990 in the eastern and western Maloti provide a baseline for assessing historical and future shifts in the abundance of functional groups such as C₃ and C₄ grasses and encroaching unpalatable dwarf Karroid shrubs. C₃/C₄ grasses had a skewed topographic distribution with the 50% floristic crossover from C₄ to C₃ grasses occurring approximately at 2 900 m above sea level (asl) on northerly slopes and 2 700 m asl and 2 400 m asl on south-facing slopes in the east and west, respectively. Shrubs were restricted to low, warm and dry slopes. C₃/C₄ grass patterns were most strongly correlated with modelled daily temperatures in early spring (October) and late summer (February), whereas winter temperatures and evaporation appeared important for shrubs. Warming would favour C₄ grasses but eCO₂ might benefit C₃ grasses, whereas unpalatable C₃ shrubs would be promoted by warming, eCO₂ and grazing and should expand their distribution. Monitoring functional groups by remote sensing is recommended.

Keywords: C₃ and C₄ grasses, grazing, Karroid shrubs, temperature, topography