Informations et ressources scientifiques
sur le développement des zones arides et semi-arides

Titre : Relationship among functional traits of wetland plants and climatic variables along an aridity gradient across the Highveld, South Africa

Auteur : Mofutsanyana, Seadi Sefora

Université de soutenance : University of the Free State

Grade : M.Sc. (Plant Sciences) 2017

Résumé partiel
Wetlands are among the most threatened ecosystems in South Africa due to human activities such as changing land use. In addition to these threats, wetlands are now faced with the threat of climate change, which may affect their biota in the future. Therefore, South Africa needs locally relevant biological indicators to detect changes in wetland ecosystems that can be used in monitoring programmes for wetland vegetation. Plant functional traits are recognised as an effective tool that can be used to understand community assembly processes that determine the abundance and distribution of plant species and their response to climate change. The aim of the study was to determine whether plant functional traits change along an aridity gradient across the Highveld of South Africa. Functional traits of the dominant plant species were collected in the wetlands of the Highveld along a climatic gradient from dry in the west to mesic in the east. The measured traits include plant weight, rhizome internode length, shoot length, leaf nitrogen content (Leaf N) and specific leaf area (SLA). In the analysis canonical ordination techniques were applied to find the correlation between plant functional composition, non-climatic environmental variables and climatic variables. Community-averaged traits were calculated for all wetland vegetation plots and these were plotted against non-climatic environmental variables and climatic variables using the CANOCO program. Hierarchical Cluster Analysis (HCA) was carried out to delineate plant functional groups using the PC-Ord program. Plant functional groups were plotted against non-climatic environmental variables and climatic variables using CANOCO program. The distribution ranges of each plant functional group were mapped using Geographical Information System (ArcGIS). Principal Component Analysis (PCA) was carried out using the PC-Ord program to find the relationship between non-climatic environmental variables and climatic variables. The RDA results showed that the correlations between climatic variables and plant traits in general are not as strong as expected ; plants seem to respond much more strongly to non-climatic environmental variables. This means that plants seem to respond much more directly to local factors that determine the wetland habitat and not directly to the climate itself. Nonetheless, it is still possible that these environmental conditions (wetness, inundation, nutrient content of the soil) may change as well in the scenario of climate change, but that would be considered as an indirect effect. The results revealed that plant weight and rhizome internode length are correlated with maximum temperature and evaporation.

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