Interactions between timber harvesting and swamp wallabies (Wallabia bicolor):: Space use, density and browsing impact

Timber harvesting in native Eucalyptus forests was used as an experimental treatment to study its effect on the space use and density of the swamp wallaby (Wallabia bicolor), and on the impact of herbivorous mammals on postharvest tree regeneration. The space use and density studies used a Multiple Before-After Control-Impact (MBACI) design to compare changes before and after (and in some cases before and during) harvesting, between unharvested control and harvested impact locations. The impact of harvesting on wallaby space use was quantified separately at two harvested sites in terms of home range size, core range size and overlap (95 and 50% fixed kernels), and the shift in geographic centre of location (GCL). The most obvious response to harvesting was a substantial shift in core range position and, in some cases, a large (> 100%) increase in home ran-e size. Relative to unharvested controls, GCLs shifted substantially farther at one harvested site but not at the other. Home range overlap tended to be similar at control and harvested sites indicating that harvesting had a minimal impact on the overall use of space. One year after harvesting, wallaby density was about five times greater at harvested sites than at control sites. This overall increase was characterised by an almost complete abandonment of harvested areas for the first 8-10 months and then a rapid influx of animals after this time. Browsing impact on 12-month-old Eucalyptus seedlings (% biomass removed) ranged from 1.0 to 11.2% but was insubstantial for coppice (0.4-0.9%). The percentage of severely damaged seedlings ranged from 0 to 12.9%. The reduction in stocking attributable to severe browsing ranged from 0 to 3% indicating that browsing impact had little effect on regeneration success. The results are discussed with reference to effective monitoring of browsing impact in commercially harvested native forests. (c) 2007 Elsevier B.V. All rights reserved.