Small mammals and retention islands: An experimental study of animal response to alternative logging practices

The integration of forest biodiversity conservation with wood production is a key part of ecologically sustainable forest management. This can be a particular challenge at the stand-level when high-intensity silvicultural systems like clearfelling are employed. Alternative logging practices to clearfelling that result in partial stand retention are being widely promoted in many parts of the world. We present new findings from a replicated block experiment designed to examine the responses of small terrestrial mammals to the retention of islands of forest within otherwise clearfelled harvest units. Our experiment was conducted in the Mountain Ash (Eucalyptus regnans F. Muell) forests of the Central Highlands of Victoria, south-eastern Australia. We quantified the effects of four treatments on small terrestrial mammal abundance: (1) an uncut ('control') area of forest; (2) a 1.5ha retained island within an otherwise clearfelled area; (3) three 0.5ha retained 'islands' within an otherwise clearfelled area; and (4) a traditionally clearfelled area of forest, over the different stages of harvesting operations from pre-cut to post-cut to post-burn.We expected to find a gradient in animal abundance from controls to large islands to small islands to clearfelled areas. Our data revealed no difference in the small animal abundance in the controls and in the islands, but significantly lower numbers of animals in clearfelled areas, particularly after regeneration burning. We believe the reason for the strong negative effect of logging is associated with the near complete removal of vegetation cover immediately following traditional clearfelling operations. We expected that large islands (1.5ha) would support more animals than small islands (0.5ha), but we found no significant difference in animal abundance between large and small islands.Our results demonstrate that retained islands support populations of small mammals despite their abundance being very low in surrounding clearfelled areas. They also suggest that residual populations in islands may promote the process of post-disturbance ecological recovery in logged landscapes.