TRENDS IN VEGETATION PATCHINESS LOSS AND IMPLICATIONS FOR LANDSCAPE FUNCTION: THE CASE OF PTERONIA INCANA INVASION IN THE EASTERN CAPE PROVINCE, SOUTH AFRICA

Abstract

ABSTRACTThe invader shrub Pteronia incana has colonised extensive areas in communal villages, commercial farms and game reserves in the Eastern Cape Province, South Africa. The spatial and temporal trends in patchiness dynamics for P. incana and their implications for landscape connectivity and functionality were analysed at the hillslope scale in one of the affected catchments. High‐resolution imagery for 2001, 2004 and 2009 was used to analyse the temporal changes in patchiness loss. Spatial metrics, namely landscape shape index (LSI), percentage of landscape (PLand) and largest patch index (LPI) were used to depict patchiness trends. Vegetation patterning was examined in the field along transects in order to determine the landscape organisation index (LOI) and characterise selected components of the landscape function analysis. Sediment sinks in the form of run‐on zones were also surveyed.Temporal trends analysed between 2001 and 2009 showed an increase in P. incana patchiness loss, as confirmed by a 75 per cent increase in the LSI, a decrease in PLand and LPI from 42·64 to 38·02 per cent and 25·98 to 20·52 per cent, respectively. The average inter‐patch length increased, and LOI decreased in a downslope direction. A progressive increase in rill density per 200 m and the development of gullies on the lower slope elements were also observed. Such increased connectivity is an indication of a trajectory towards hillslope dysfunctionality. The presence of run‐on zones within microtopographic concavities on the hillslope units provides isolated elements of functionality in the hillslope systems. These zones are recommended as starting points in restoration efforts. Copyright © 2012 John Wiley & Sons, Ltd.