Topographic regulations on ecohydrological dynamics in a montane forest catchment and the implications for plant adaptation to environment

Rugged and covered by vegetation, most of the Earth's terrestrial surfaces constantly interact with ecohydrological processes and influence ecosystem functioning and stability. To understand how water and vegetation interact in adaptation to environmental change under topographic regulations, we conducted an experiment in a montane catchment in South Australia during 2012–2014. We presented the dynamics of microclimate, soil moisture and transpiration (E_c) in two plots on the north- and south-facing slopes (NFS and SFS), and discussed how plants may adapt to environment with varied water and energy availabilities. It was found that (1) the maximum E_c occurred in spring when both energy and water supplies were optimal for tree growth, whilst the minimum appeared in autumn mainly related to soil water deficit; (2) the largest differences in E_c from two eucalyptus species were in winter (NFS > SFS) and summer (SFS > NFS) related to seasonal variations of radiation and soil water modulated by terrain aspect; (3) faster and greater soil water depletion on NFS than SFS in dry seasons was most likely resulted from evapotranspiration; and (4) total plot transpiration was similar on the opposite slopes despite the topography-induced seasonal differences. The species on SFS were less vulnerable than those on NFS in dry environments reflected by relatively higher transpiration. Our results may indicate that antecedent soil water storage and the following dry-season replenishment are particularly important for tree survival especially those on the equator-facing slopes. The comparisons have sound implications for understanding the ecohydrological dynamics and hillslope forest management in semi-arid areas.