To what extent does urbanisation affect fragmented grassland functioning?

• Published in: Journal of environmental management 2015-03, Vol.151, p.517-530
• Main Authors: van der Walt, L., Cilliers, S.S., Kellner, K., Du Toit, M.J., Tongway, D.
• Format: Article
• Language: English
• Subjects: Agriculture; Cohabitation; Conservation; Conservation of Natural Resources; Environmental impact; Fragmentation; Fragments; Grassland; Grassland fragments; Grasslands; Humans; Indicators; Landscape; Landscape ecology; Landscape function; Landscape metrics; Landscapes; Mining; Mowing; Soil (material); Soil surface indices; South Africa; Urban areas; Urbanisation gradient; Urbanization; Vegetation
• ISSN: 0301-4797; 1095-8630
• DOI: 10.1016/j.jenvman.2014.11.034

Urbanisation creates altered environments characterised by increased human habitation, impermeable surfaces, artificial structures, landscape fragmentation, habitat loss, resulting in different resource loss pathways. The vulnerable Rand Highveld Grassland vegetation unit in the Tlokwe Municipal area, South Africa, has been extensively affected and transformed by urbanisation, agriculture, and mining. Grassland fragments in urban areas are often considered to be less species rich and less functional than in the more untransformed or “natural” exurban environments, and are therefore seldom a priority for conservation. Furthermore, urban grassland fragments are often being more intensely managed than exurban areas, such as consistent mowing in open urban areas. Four urbanisation measures acting as indicators for patterns and processes associated with urban areas were calculated for matrix areas surrounding each selected grassland fragment to quantify the position of each grassland remnant along an urbanisation gradient. The grassland fragments were objectively classified into two classes of urbanisation, namely “exurban” and “urban” based on the urbanisation measure values. Grazing was recorded in some exurban grasslands and mowing in some urban grassland fragments. Unmanaged grassland fragments were present in both urban and exurban areas. Fine-scale biophysical landscape function was determined by executing the Landscape Function Analysis (LFA) method. LFA assesses fine-scale landscape patchiness (entailing resource conserving potential and erosion resistance) and 11 soil surface indicators to produce three main LFA parameters (stability, infiltration, and nutrient cycling), which indicates how well a system is functioning in terms of fine-scale biophysical soil processes and characteristics. The aim of this study was to determine the effects of urbanisation and associated management practices on fine-scale biophysical landscape function of urban and exurban grassland fragments, as well as to determine the potential for the use of LFA in decision-making involving the conservation of grassland fragments. The results indicated that the occurrence, size and characteristics of vegetated patches, and especially the presence of litter abundances, were the main factors determining differences in the LFA indices. Furthermore, mowing resulted in the overall fine-scale biophysical indices being higher for some of the urban grassland fragments. This implied that it i