The importance of trees as nesting and foraging sites was investigated for 12 species of small, native, ground-dwelling mammals in 13 forests in southeastern and southwestern Australia. At least half of all observed foraging occurred on tree surfaces or hollows, loose bark, logs or leaf litter; limited observations were made of foraging on open ground or among shrubs or rocks. Most observations (86%) of above-ground foraging were in large, mature trees with complex branching systems. In forests dominated by ribbon gum Eucalyptus viminalis, the suitability of trees as foraging substrates for insectivorous mammals changed seasonally with the peeling of bark; in spring the trees harboured rich populations of invertebrates under the detaching bark, but after bark peeling in summer, invertebrates migrated to the bases of the trees or the ground. Nest and shelter sites occurred mostly in hollows in mature or senescent trees, in logs or leaf litter. These findings suggest that the requirements of several species of terrestrial mammals are best met by large, mature trees and a complex ground layer that includes logs and leaf litter. Some management recommendations are that: 1. logging cycles be extended to allow hollow formation; 2. areas with large or diverse populations of ground-dwelling species be set aside or only selectively logged; 3. control burning be minimized to allow retention of nest and foraging sites; 4. logged areas be widely separated within forests to maintain structural diversity; and 5. research be initiated to determine the long-term effects of different forestry operations on the numbers and diversity of ground-dwelling mammals.