Effects of Rabbit Grazing and Fire on a Subalpine Environment. II. Tree Vegetation

Abstract

The effects of two low-intensity fires andlor grazing by rabbits and wombats upon trees of Eucalyptus pauciflora and E. stellulata. in a subalpine environment were studied between 1977 and 1984. The experimental plot design permitted comparisons to be made between unburnt and burnt areas, each of which was subjected to four grazing regimes. Tall shrubs, mainly Bossiaea foliosa, which were present under the trees during the first fire but not the second increased fire intensity and flame height and hence damage to trees. The first fire in March 1978 did not completely kill any trees, but killed all the stems 2 m or more in height on 34% of trees and stimulated basal regrowth on a further 17% without killing all the stems. The first fire also reduced the basal area of live stems by about 17%. Small saplings less than 2 m high and seedlings were generally top-killed but resprouted from the base. In the second fire only lignotub- erous regrowth and seedlings were affected as they were in the first fire; the older trees showed no sign of damage. Rabbits killed a significant number of trees by first ring-barking the stems and then grazing the regrowth. Both the fires facilitated the establishment of tree seedlings in the frost-hollow by exposing bare soil, but few of these seedlings survived to the end of the 7-year study period. Frost was probably the main cause of tree death, but drought and competition from other species may also have contributed to losses.