Trends in Soil Erosion and Woody Shrub Encroachment in Ngqushwa District, Eastern Cape Province, South Africa

Abstract

Woody shrub encroachment severely impacts on the hydrological and erosion response of rangelands and abandoned cultivated lands. These processes have been widely investigated at various spatial scales, using mostly field experimentation. The present study used remote sensing to investigate spatial and temporal patterns of soil erosion and encroachment by a woody shrub species, Pteronia incana, in a catchment in Ngqushwa district, Eastern Cape Province, South Africa between 1998 and 2008. The extreme categories of soil erosion and shrub encroachment were mapped with higher accuracy than the intermediate ones, particularly where lower spatial resolution data were used. The results showed that soil erosion in the worst category increased simultaneously with dense woody shrub encroachment on the hill slopes. This trend is related to the spatial patterning of woody shrub vegetation that increases bare soil patches--leading to runoff connectivity and concentration of overland flow. The major changes in soil erosion and shrub encroachment analysed during the 10-year period took place in the 5-9° slope category and on the concave slope form. Multi-temporal analyses, based on remote sensing, can extend our understanding of the dynamics of soil erosion and woody shrub encroachment. They may help benchmark the processes and assist in upscaling field studies.

Effects of different management regimes on soil erosion and surface runoff in semi-arid to sub-humid rangelands

“…We note that abandoned degraded rangelands are frequently found in semi-arid rangelands, where woody encroachment and desertification are major problems (e.g. Muñoz-Robles et al, 2011;Puttick et al, 2011;Manjoro et al, 2012). Although many studies claim to study overgrazed rangelands, we found them to mostly focus on high intensity grazed rangelands instead.…”

“…Along the typology, vegetation cover changes from mature vegetation (natural rangelands) to more grassy species (low intensity grazed) and introduced grass and herbaceous species (high intensity grazed). Overgrazed rangelands are characterised by bare soils and woody encroachment, whereas abandoned degraded rangelands are suffering from desertification and increased woody encroachment (Puttick et al, 2011;Manjoro et al, 2012). Rangeland degradation involves irreversible changes in both soils and vegetation (Fynn and O'Connor, 2000).…”

Woody encroachment and forest degradation in sub-Saharan Africa's woodlands and savannas 1982–2006

“…Tree canopy area increased by 10-fold in 35 years[32]m. South Africarangelands and abandoned cultivated land33°16’ S, 27°8’ Eanalysis of multi-spectral SPOT images11.5% increase in ‘slightly eroded (dense bush)’ category 1998–2008[33]n. South Africasavanna woodland, different management types28°02’ S, 32°12’ Efield transect evaluation and aerial photograph analysistotal tree cover increased from 14% in 1937 to 58% in 2004 in a conservation area, from 3% to 50% in a commercial ranching area, and 6% to 25% in a farmed area[34]o.…”

Restoration potential of invaded abandoned agricultural fields: what does the seed bank tell us?

“…Summers are warm (December to March: average daily maximum of 26°C) and winters are mild (June to August: average daily minimum of 7.5°C). Red mudstones and shale underlie the area (Manjoro et al ), resulting in soils which are shallow and rocky, and high in swelling hydrous mica clays (Kakembo ). Additionally, the soils are highly dispersive and low in organic matter, often resulting in surface crusting and erosion (Kakembo et al ).…”