The control of the encroaching shrub Seriphium plumosum (L.) Thunb. (Asteraceae) and the response of the grassy layer in a South African semi-arid rangeland

Abstract

Large-scale bush encroachment within rangelands is of increasing concern for land users. The aggressive encroachment of the woody shrub Seriphium plumosum (L.) Thunb. (Asteraceae), previously known as Stoebe plumosa, has resulted in a reduction in productivity, causing large socio-economic challenges, such as loss of productive land. In this study, we evaluated the efficacy of four herbicides in combination with mechanical removal of S. plumosum. We measured shrub mortality, regrowth and examined the grass species richness and cover after the execution of the control methods. Furthermore, we compared the productivity of the paddock where S. plumosum had been controlled with a neighbouring unencroached paddock. Five months after herbicide application, the total mortality of all shrubs was recorded. Grass species richness and cover were higher when shrubs had been mechanically removed before herbicide application. Additionally, the use of the non-speciesspecific herbicide (tebuthiuron) resulted in lower species richness and cover, compared to application of a speciesspecific herbicide (metsulfuron-methyl). The productivity of the treated area increased in the year after application. Our results show that when controlling S. plumosum the manual removal of shrubs before applying herbicides can improve the regeneration of the grass layer. This combination of mechanical and chemical control is effective in combating S. plumosum encroachment and increases forage yields in semi-arid rangelands.