Tree hollows as a resource for wildlife in remnant woodlands: spatial and temporal patterns across the northern plains of Victoria, Australia

Abstract

Hollows in living or dead trees are an important resource for a range of animal species in Australia. They are used for diurnal and nocturnal shelter and as breeding sites, and the availability of hollows may be a limiting factor for some populations. This study examined patterns in the distribution of tree hollows at 185 sites, each of 1.0 ha, in remnant woodlands across the northern plains, Victoria, a rural region where little remains of the natural woodland cover. Spatial and temporal variation in the abundance of tree hollows is evident at several scales including that of the individual tree, the landscape and the region. For individual trees, the number of holes increased with tree diameter, and the slope of this relationship differed between tree species. The percentage of trees that are hollow-bearing also differs between species. Large trees have a higher proportion of holes with a large entrance diameter (>10 cm) and a lower proportion of small holes (?2 cm diameter) than do small trees. At the landscape scale, hollow-bearing trees were not evenly distributed throughout remnant woodlands. Significant variables in a regression model of the abundance of hollow-bearing trees included: the number of large trees (>70 cms diameter), woodland tree species composition and mean annual rainfall. At the regional scale, the availability of hollows is influenced by the patchy distribution of remnant woodlands. Large tracts are mainly associated with public land along river systems and contrast with extensive areas of farmland where woodlands are sparse or absent. The abundance of hollows at the landscape and regional scale is strongly influenced by the impact of land management on two key processes; the loss of existing hollow-bearing trees and the recruitment of new trees. On privately managed land, generally grazed by domestic stock, large trees with hollows are often present, but the scarcity of saplings and small trees raises concern over the recruitment of future hollow-bearing trees, and indeed the long-term persistence of woodland vegetation. Conversely, most sites in large blocks of public land have ample regeneration but relatively fewer hollow-bearing trees due to the loss of larger trees from timber harvesting activities. In both situations, the abundance of trees with hollows is the consequence of management practices, and their future availability is directly amenable to management action. Some implications of the patterns of distribution of hollows for wildlife are discussed.