Revegetation of bare patches in a semi-arid rangeland of South Africa: an evaluation of various techniques

摘要

Semi-arid rangelands, which have retrogressed beyond a certain threshold and could not rest-recover, can only be restored by mechanical inputs helping the re-establishment of vegetation. Therefore, different over-sown species and mechanical restoration methods (hollows-dyker plough, furrows-ripper/sub-soiler and walking-stick planter) were evaluated for the restoration of bare areas on both a sandy and clayish soil type. Changes in species composition and plant density over time (1987/88-1996/97 growing seasons) were determined. The hollows with a rip action in one cultivation operation remained over a longer period and therefore caught more water for better establishment of grass species, compared with making only hollows where it silted up more easily. Establishment was poorest when only the walking-stick planter was used. Although the well establishment of Eragrostis curvula over the first 3 years, after 10 years only a few plants survived in both clay and sandy soils. Regardless of cultivation treatment or soil form, Digitaria eriantha subsp. eriantha survived the best (p<0.01) after 10 years and even spread into adjacent areas. Anthephora pubescens and Cenchrus ciliaris only established successfully in sandy soil. Restoration in semi-arid rangelands is slow and failures are common because of low and unreliable rainfall.