A multi-dimensional assessment of land degradation in the Sterkspruit river catchment: the nexus between landscape sensitivity, land use dynamics and landscape resilience.

Abstract

This study sets out to assess the status and causes of land degradation in the Sterkspruit catchment of the Eastern Cape, and the extent to which this has affected the biophysical environment and rural livelihoods. The attributes of the biophysical and socio-economic environments that predispose the area to land degradation, the manifestations of land degradation and people’s responses to the dynamics of their environmental circumstances are some of the key issues of enquiry. This research pursued a multidimensional approach to land degradation assessment, looking at numerous criteria on multiple scales. The landscape-scale component of the study included detailed analysis of climatic data to provide a backdrop for land degradation. It also entailed developing and analyzing land use-land cover maps of Sterkspruit catchment, based on LANDSAT TM satellite imagery of medium resolution (30m x 30m). Ground-truthing, transect walks at several pre-selected locations, followed. Participatory rural appraisals (PRAs) and questionnaire surveys on rural livelihoods, householders’ experiences as well as their perceptions of land degradation, and their responses to it were conducted in the catchment’s villages of Magwiji and Hinana. Site-specific survey involved identifying sample sites at various stages of degradation, visually assessing them and generating degradation indices, adopting a multidimensional analysis technique using several soil- and vegetation-related variables. It also involved vegetation condition assessment through rangeland transect sampling, recording data for basal cover, species dominance, biomass productivity, and the presence of indicator species, such as decreasers and increasers. Estimates of soil loss at sites were done through measurements of gullies, rills, and pedestals, and calculation of volumes lost per unit area. In situ soil degradation was assessed through field measurement of infiltration capacity and soil penetration resistance. From the study sites, soil samples were collected and analyzed in the laboratory for soil bulk density and for the chemical indicators EC, pH, organic C, Na, K, Mg, Calcium, available P, and total P. Study results showed manifestations of land degradation in various forms. The LU-LC analysis indicated that bare ground appeared in dry seasons and in drought years; vegetation recovered with the return of the rains. The land degradation index (LDI) showed eight out of 21 sites as extremely degraded, while the rest were, seriously to moderately, degraded. The largest amounts of soil loss were from sheet erosion, followed by heavy losses from gully erosion, especially in Hinana village. Another manifestation of degradation was the loss of grazing land to gully encroachment. Soil bulk density tests showed serious compaction in four sites; the rest of the sites were either slightly compacted or not compacted. Vegetation transect surveys, showed an increase in unpalatable grass species (increaser II) and bush encroachment on grassland. Chemical indicators were as follows: EC indicated strongly saline soils; K levels were good, making plants drought-tolerant; excessive amounts of Ca and Na made the soils dispersive, predisposing them to erosion; Mg amounts were adequate; total P was high-to-medium on 13 sites, low on eight sites; organic C was low on all sites, indicating low fertility and deficiencies in N, P, and boron. Causes of degradation include sustained grazing pressure in a drought-prone environment. Residents’ responses included rehabilitating degraded land, cutting down on arable agriculture as a risk avoidance strategy, and providing supplementary feed to livestock. Livelihood changes showed a trend towards the use of communal lands for residential purposes rather than for farming, while subsisting on government grants and pensions