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).