Vegetation responses to seasonal weather conditions and decreasing grazing pressure in the arid Succulent Karoo of South Africa

Response of Kalahari vegetation to seasonal climate and herbivory: Results of 15 years of vegetation monitoring

“…It also showed a positive response to humid conditions towards the end of the dry season in late winter (SPEI JAS) and in early summer (OND) preceding the vegetation assessment. The findings coincide with the outcome of the time-series analysis from the arid winter-rainfall region of South Africa, where cover of dwarf shrubs showed a strong positive response to rainfall and SPEI at the end of the dry period in the winter rainfall region (Schmiedel and Oldeland, 2018).…”

“…The SPEI integrates rainfall and temperature and is thus a better proxy for the climatic conditions relevant for plant life than rainfall alone. The relatively few scholars who included SPEI in their models for population or vegetation dynamics could already show the strength of the integrated predictor (Van Rooijen et al, 2015;Schmiedel and Oldeland, 2018;Tenhumberg et al, 2018). In addition, our models revealed that in contrast to total annual rainfall seasonal SPEI is a suitable proxy for the growing conditions of the eight life forms that differed in their responses.…”

“…Total annual rainfall, in contrast, played no role at all. Even though some long-term observation studies' authors employed annual rainfall as a potential driver for vegetation change (Buitenwerf et al, 2011;Masubelele et al, 2015), many studies showed the importance of the intra-annual climatic variance for the vegetation dynamics (Veenendaal et al, 1996;Swemmer et al, 2007;Dreber and Esler, 2011;Lohmann et al, 2012;Schmiedel and Oldeland, 2018). The strong responses of the abundant annual life forms (annual graminoids, annual forbs) and of dwarf shrubs to seasonal climatic conditions (Table 2a) support these findings.…”

Introduction to the Karoo Special Issue: Trajectories of Change in the Anthropocene

“…This tendency was confirmed in a nature reserve, where perennial shrubs provided the veld with better drought tolerance than annual plants, although temporarily high densities of game caused palatable shrubs to give way to unpalatable species, thereby reducing the long-term grazing capacity of the rangeland (van Rooyen et al 2018). Even after long-term exclusion of large herbivores, recovery from conditions of grazing pressure is extremely slow and grazing-induced degradation and the decline of shrub cover can continue for several decades (Schmiedel and Oldeland 2018), as can the prevalence of unpalatable species (Arena et al 2018). All long-term studies presented in this KSI (op.…”

“…Long-term ecological research, including field experiments, provides excellent insights into changes and their drivers in the Karoo, particularly as this research concerns long-term changes over space and time (Arena et al 2018;du Toit et al 2018;Nenzhelele et al 2018;Schmiedel and Oldeland 2018;van Rooyen et al 2018). Site-based experiments and observations at Grootfontein straddling eight decades since the 1930s (the oldest grazing trials in the world) have revealed that above-average rainfall between the late 1970s and mid-2010s has resulted in the eastern biome boundary of the Nama-Karoo being grassier than before (du Toit et al 2018).…”