Conservation of fragmented grasslands as part of the urban green infrastructure: how important are species diversity, functional diversity and landscape functionality?

Abstract

Natural remnants, such as fragmented grasslands form an integral part of the urban green infrastructure in the Grassland biome of South Africa. Nearly 30 % of natural grasslands are transformed with only 1 % formally conserved. Since grassland habitats are globally regarded as a biodiversity conservation priority, protection should be accorded outside formal conservation areas as well. However, urban grassland fragments are often regarded as highly transformed, and are therefore targeted for development rather than conservation. The aim of this study was to compare plant species composition, −diversity and -functional diversity, as well as the fine-scale biophysical landscape functionality of grassland fragments in urban and exurban areas in the vulnerable Rand Highveld Grassland vegetation type in the Tlokwe Municipal area of South Africa. Thirty selected grassland fragments were investigated along an urbanisation (urban-exurban) gradient that was quantified using several demographic- and physical variables as well as landscape metrics, each reflecting a pattern or process associated with urbanisation. Plant species composition, −diversity, and -life history traits were determined in randomly selected sample plots. Functional diversity indices were also calculated to describe the composition and distribution of plant functional traits in the selected grassland fragments. Additionally, landscape functionality, in terms of how effectively the landscape is functioning as a biophysical system, was determined using the Landscape Function Analysis (LFA) method. LFA provides information such as fine-scale resource conserving patchiness, soil surface stability, infiltration, and nutrient cycling. The fine-scale biophysical landscape function of urban and exurban landscapes are comparable, indicating that urban grassland fragments are worthy of conservation on a biophysical landscape function scale. However, differences in plant species diversity, functional trait composition, and plant functional diversity were evident.