The ecology of a stressful site: Mount To wrong, Central Victoria 1967–1997

Abstract

Summary Species on Mt Towrong are distributed along soil moisture gradients which are dictated chiefly by aspect, altitude, soil depth and proximity to drainage lines. On the warm and dry western aspect large areas of shallow, rocky soils alternate with bands of deeper soils. On the cooler eastern aspect, soils are relatively deep throughout. Drought damage has occurred on the rocky soils of the western aspect six times in the last 25 years, whenever the annual rainfall was less than about 50% of the long-term mean. Fires are also recurrent perturbations that are most severe in drought years, especially when accompanied by hot NW winds. The fire of 1983 caused severe damage over the whole western aspect of Mt Towrong. Damage on the eastern lee slope was much less severe. An assessment of relative recovery of tree species from these perturbations was based on various combinations of species pairs growing in close proximity to one another. Hie rank order of drought resistance was Allocasuarina verticillata > Eucalyptus goniocalyx > E. radiata > E. obliqua (= E. viminalis) which was the reverse of that in relation to fire+ drought, that is, E. obliqua > E. radiata = E. goniocalyx > Allocasuarina verticillata. Seedling regeneration of tree species in the inter-drought periods was meagre but nevertheless the most mesic species, E. obliqua, consistently dispersed onto adjacent dry rocky sites, only to be killed in each of the ensuing drought periods. After fire, seedling regeneration of eucalypts (especially E. obliqua) was generally prolific, although the vigour and density of seedlings was patchy and related to the pattern of redistributed nutrient-rich hillwash. After 10–12 years, survival of the best seedlings was evident only in gaps in the reconstituted canopy. On this stressful site the indigenous species have been resilient to serious perturbations of the environment. It seems likely that, for the retention of species on a site, frequencies of fires and droughts may be more critical than the occasional exceptionally severe event.