Assessing environmental factors contributing to plant species richness in mountainous mesic grasslands

Abstract

Southern African mountain ranges are characterised by rich and diverse plant species thriving in different habitats with pronounced endemic species. However, globally, biodiversity at the species level is deteriorating rapidly because of environmental change leading to habitat degradation and fragmentation. Mountainous grassland communities are particularly vulnerable to rapid ecosystem changes because of their specialised niches and sensitivity to global warming. Understanding the determinants of vegetation is necessary for effective and efficient management. This study aimed to determine significant environmental drivers influencing plant species richness in mountainous mesic grasslands. Topographical variables (slope and elevation) were derived by using a 30 m resolution Digital Elevation Model. Soil variables such as bulk density, silt fragments, pH, coarse fragments, soil organic carbon, sand and nitrogen were acquired from the International Soil Conference and Information Centre (ISCI), and species richness and diversity were derived from vascular plant species inventory data compiled using a field survey. Species richness was influenced by soil bulk density, and the interaction between elevation and soil bulk density; higher species richness was associated with lower bulk density and higher elevations. Similarly, species composition changed as edaphic factors and elevation changed.

Conservation implications: Species richness increased with soil bulk density, which decreased with elevation. Fire severity had little effect on species richness and diversity, which may indicate that management actions do not affect species. However, the impact of grazers still needs to be better understood at this time. Moreover, the strong positive relationship between species richness and diversity in this study shows that species richness can be used as a surrogate for diversity and conservation monitoring, especially in mesic highland grasslands.