Growing on rocky ground: Microhabitat predictors for site-occupancy of Aloe peglerae, an Endangered endemic species with a restricted range

Abstract

Succulent aloes of savanna and grassland ecosystems have adaptations to fire but favourable local-scale microhabitat conditions can further support plant growth, reproduction, and survival. However, due to the heterogeneity in habitat structure, it may be unclear what type of microhabitat predictors are important for aloe conservation, and hence mismanagement of plants with restricted ranges may cause declines and/or local extinctions. This study compared the seasonal differences of aloe-occupied (n=100) and aloe-vacant (n=100) microhabitats for Aloe peglerae, an Endangered endemic of the Magaliesberg and Witwatersberg mountain ranges in South Africa. The aim was to determine key microhabitat predictors of aloe persistence in a fire-mediated savanna during the wet and dry seasons. Twelve microhabitat variables were measured within circular plots around each aloe-occupied and aloe-vacant microsite (0.5m radius). Aloe-occupied microsites in both seasons were strongly associated with typical ‘safe site’ microhabitat conditions comprising a higher average rock cover (aloe-occupied site=56%; aloe-vacant site=42%), lower bare ground cover (12%; 21%), lower grass cover (25%; 32%), lower above-ground biomass (1,079kg.ha-1; 1,616kg.ha-1), and higher forb cover (4.8%; 3.3%). A discriminant function analysis model for summer indicated the strongest microhabitat predictors of site discrimination were rock, grass, and bare ground cover. The strongest predictors of site discrimination for the winter model were bare ground cover, plant litter cover, and above-ground biomass. Thus, Aloe peglerae persists in rocky safe sites of low surrounding vegetation, providing increased fire-protection. Fire exclusion and the resultant increase in biomass and woody vegetation (bush encroachment) may thus be detrimental to the long-term persistence of Aloe peglerae.