Study area
The study was conducted at Buffelskloof Private Nature Reserve (25⁰ 19’ 22.21” S, 30⁰ 29’ 15.41” E), Mpumalanga, South Africa. Buffelskloof supports vegetation types from three biomes: Afromontane forest, mid-altitude savanna and montane grassland (Mucina and Rutherford, 2011). The reserve is approximately 1500 ha in size with an altitudinal variation of 1000 to 1800 m (Buffelskloof Nature Reserve, 2019). Samples were collected between 1314 and 1477 m elevation.
Within the grassland and savanna vegetation on Buffelskloof, bush clumps (BCs) have been establishing (Jamison-Daniels et al. , 2021). A BC is defined as an association of one or more trees (> 1.2 m) with tree saplings (< 1.2 m) growing beneath the canopy, that are separated from each other by grassy vegetation (Jamison-Danielset al. , 2021). A space-for-time substitution study, in which the woody vegetation of 40 BCs ranging in size from 10.05 m2 to 1342.99 m2 (mean = 266.41 m2, SE = 347.75 m2) was characterised, where it was found that the formation of these BCs follows a deterministic trend of succession in woody species, with a turnover from open-habitat trees to shade-tolerant trees as the BCs increase in size (Jamison-Daniels et al. , 2021). These directional changes in tree community composition are driven by directional changes in microclimatic conditions (temperature, soil moisture and humidity) and light availability as BCs increase in size (Jamison-Daniels et al. , 2021).