Plant–soil interactions in lower–upper montane systems and their implications in a warming world: a case study from the Maloti-Drakensberg Park, southern Africa

The potential impacts of climate change on mountain environments are gaining increasing attention given the inherent fragile nature and high biodiversity value of mountain biota. We pay particular attention to the soil–plant–climate interface given that such interactions and trade-offs may exert a strong influence on how plant species will respond to climate change in mountain environments. Our study site in the Maloti-Drakensberg Park, Drakensberg Mountains (southern Africa), is located at the juncture of two climato-ecological belts with relatively well-partitioned vegetation communities that should therefore allow vegetation shifts to be easily detected. We believe that this treeline ecotone is a key temperature threshold area and is therefore an ideal boundary to use for climate change research. Soils sampled from this ecotone revealed a broad suite of high nutrient levels, indicative of soils derived from nutrient-rich flood basalts, with the exception of key growth-limiting nutrients, i.e. available phosphorus and nitrogen. Together with other soil and site characteristics such as high soil organic matter and clay fractions, low temperatures, high rainfall and steep topography resulting in nutrient leaching and low pH soils, we reason that the soil nutrient economy in the Maloti-Drakensberg Park is more constrained than previously thought. This is also supported by the plant communities sharing strong links to the Cape Floristic Region, characterised by intrinsically nutrient-poor soils. Given the increased pool of soil nutrients potentially available under a warming regime, we propose a research framework outlining key areas of investigation given the potentially disastrous implications for plant biota adapted to a nutrient-poor soil environment.