Changes in plant functional composition of wetland vegetation along an aridity gradient on the Highveld plateau of South Africa

Abstract Question Plant communities will change along environmental gradients, even in “azonal” vegetation such as wetlands. It is hypothesized that functional community composition of wetland vegetation changes along a natural gradient from dry low‐lying areas to wet high‐lying areas. We wanted to know how the functional groups that make up wetland plant communities change along such aridity and altitudinal gradients. Location Highveld area of Central South Africa, covering four provinces of the country: Northern Cape, Free State, North West and Mpumalanga. Methods The community composition of 201 vegetation plots was obtained from a compilation of South African wetland vegetation types of the study area. Functional traits were collected for the dominant plant species and community‐weighted means of plant functional traits were calculated for wetland vegetation plots. Redundancy analysis was performed to plot these against environmental and climatic gradients. Results The ordination results showed that the community‐weighted plant functional traits were correlated with environmental and climatic variables. For example, specific correlations reveal that root/shoot biomass ratio, leaf nitrogen and specific leaf area are associated with high temperature and evaporation, conditions that prevail in the driest end of the gradient. On the opposite end, wetland vegetation in mesic areas has adaptations for fast growth and high productivity, as it is composed of tall plants with wide stems and deep roots. A hierarchical cluster analysis (HCA) resulted in nine plant functional groups, with different representation along the aridity gradient in the Highveld Plateau of South Africa. Conclusions Wetlands in dry areas have plant functional groups different from those in mesic areas. Changes in community composition show how wetlands are responding to climatic variability and environmental change. Thus, the study of changes in plant functional groups can be useful for detecting the impacts of climate change on wetland vegetation.