MODELING DISTRIBUTIONS OF ARBOREAL AND GROUND-DWELLING MAMMALS IN RELATION TO CLIMATE, NUTRIENTS, PLANT-CHEMICAL DEFENSES AND VEGETATION STRUCTURE IN THE EUCALYPT FORESTS OF SOUTHEASTERN AUSTRALIA

Numerous studies over the past 15 years have investigated relationship s between the distributions of arboreal and ground-dwelling mammals an d environmental, structural and leaf compositional variables in the te mperate Eucalyptus forests of southeastern and northeastern New South Wales, Australia. This paper draws together the general trends emergin g from these studies and identifies some clear messages for the future modelling of regional biodiversity in these forests. The studies on a rboreal mammals (all are marsupials in these forests) reviewed here ge nerally fall into two broad categories: those that conclude that the n utrient status of forests is the prime determinant of habitat quality for arboreal marsupials and those that put equal or greater emphasis o n variables related to structural characteristics of forests. Recent s tudies suggest a hierarchical model that is consistent with both of th ese emphases. They postulate that a proportion of temperate eucalypt f orests, regardless of their climatic or structural characteristics, ca nnot support permanent populations of arboreal marsupials, especially leaf-eating species, due to low food quality and/or high phytochemical toxicity. Above a postulated nutritional or phytotoxicological 'thres hold', food quality is adequate and other variables, including climati c and structural ones, apparently interact to determine habitat qualit y. Hence, differences in the extent to which different studies sample regional environmental variability, the range of nutrient status and f orest structure, are likely to greatly affect which variables appear m ost significant in models of habitat requirements. Structural characte ristics (measured as habitat complexity) of the forest have emerged as explanatory variables for the ground-living mammals also, Variables s uch as nutrients, lithology, terrain and climate exhibit a different t rend to that seen for arboreal marsupials. Relative abundance of small ground-dwelling mammals is negatively correlated with site nutrient s tatus as indicated by nutrient concentrations in tree foliage. Small m ammals are present at all measured nutrient levels, but their abundanc e falls substantially as habitat complexity decreases. The influence o f nutrients is masked in habitats of high complexity, there being no r elationship with nutrient status. Many ground-living mammals occur acr oss the gradients of lithology, terrain and climate, although there is wide variation in relative abundance for some species. The importance of structural variables for explaining distributions of both arboreal and ground-living fauna in eucalypt forests indicates that adequate m odelling of habitat requirements for these fauna can only be achieved if surveys obtain adequate data on forest structure to encompass gradi ents in seral stage and disturbance history. The present-day mammalian fauna of the southeastern Australian forests has been influenced stro ngly by the effects of urbanisation, clearing for farming, forestry ac tivities and fire on forest structural complexity and nutrient dynamic s as well as by predation by introduced carnivores. While modelling wi th respect to broadly defined climatic and terrain variables might be useful for broad-scale spatial prediction of faunal distributions, suc h models are unlikely to provide descriptions of habitat requirements or predictions of impacts of forest management at a scale necessary fo r sustainable management of faunal biodiversity.