The vacant planting: limited influence of habitat restoration on patch colonization patterns by arboreal marsupials in south-eastern Australia

Abstract

Many key questions remain unresolved about how biodiversity responds to temporal increases in native vegetation cover resulting from extensive restoration efforts. We quantified occupancy and colonization probability of old growth, regrowth and planted woodland patches by arboreal marsupials within Australian agricultural landscapes subject to woodland restoration over an 11 year period. Our analyses focussed on the Common Brushtail Possum (Trichosurus vulpecula) and Common Ringtail Possum (Pseudocheirus peregrinus). We found strong evidence of a gradient in occupancy levels ranging from highest in old growth woodland, approaching zero in plantings, with regrowth woodland intermediate between these two broad types of vegetation structure. Plantings were not occupied by either species at the outset of our investigation and were rarely colonized throughout the subsequent 10 years. We hypothesize that a lack of shelter sites in large old hollow-bearing trees is one of the key factors limiting the occurrence of plantings by cavitydependent arboreal marsupials, suggesting a lag between planting establishment and the time required for plantings to become suitable habitat. We found the probability of colonization was positively related to the amount of vegetation cover in the surrounding landscape. Unexpectedly, colonization probability was not influenced by a temporal increase in woody vegetation cover surrounding a patch. A paucity of relationships between patch colonization and the temporal change in vegetation cover may be explained by the fact that most of the increased vegetation cover in our study landscapes over the past decade has resulted from establishment of plantings which are generally not suitable nesting habitat for arboreal marsupials. Our findings have key management implications such as emphasizing the value of old growth woodland for arboreal marsupials and of targeting restoration efforts around old growth and regrowth woodland patches, and the flawed notion of biodiversity offsets that allow replantings to compensate for clearing old growth woodland.