The loss of vegetation cover has distinct but short-term impact on multiple vertebrate taxa in a grassland ecosystem

Abstract

Vegetation cover in grasslands typically fluctuates over time, for example, declining with grazing and disappearing entirely with burning. This temporal change in vegetation cover may impact the composition of vertebrate communities by altering habitats or perceived predation pressure. We manipulated vegetation cover in a high-elevation (ca. 1240–1500 m above sea level) grassland ecosystem and measured its effect on the community structure of birds and small mammals using a Before-After-Control-Impact study design. We established 12 plots (each plot 100 × 100 m) at Telperion Nature Reserve, Mpumalanga, South Africa, which were assigned to three treatments: mowed with cut grass left in situ (mowed-litter), mowed with cut grass cleared (mowed-cleared), and non-mowed (control). We sampled birds and small mammals over three sampling periods: before the treatment (August 2019), immediately after the treatment (October 2019), and three months after treatment (January 2020). We used point counts and Sherman live traps to surveys birds and small mammals, respectively. We observed a total of 2801 individuals of 38 species of birds and 98 individuals of eight species of small mammals. Species richness and diversity of small mammals and birds was significantly higher in the non-mowed plots compared with the mowed plots. Birds also showed differences in community composition in mowed and non-mowed treatments immediately after mowing but these differences disappeared three months after mowing, whereas small mammal composition did not differ before and after mowing. The best performing generalized additive model showed that vegetation biomass had a significant positive influence on bird species richness but not rodents. On the other hand, diversity of both taxa was significantly influenced by grass biomass. Our study suggests that loss of vegetation cover in grasslands has significant short-term effects on birds and small mammals, but that these faunal communities rapidly return to pre-loss conditions within a few months. Hence controlled vegetation removal (e.g. mowing) could be considered an appropriate tool for managing these high-elevation grasslands.