Quantifying drivers of decline: A case study of long-term changes in arboreal marsupial detections

Using a 26-year dataset, we quantify temporal change in detections of arboreal marsupial species in the tall, wet montane ash forests of mainland south-eastern Australia. We sought to determine if temporal patterns in the number of arboreal marsupial detections were associated with temporal changes in potential explanatory variables, such as stand age and abundance of hollow-bearing trees. Our key findings were: (1) Four species were characterised by an overall decline in detections over time, although sometimes in complex, non-linear ways. Exceptions were the Common Ringtail Possum (Pseudocheirus peregrinus) which increased, and the Mountain Brushtail Possum (Trichosurus cunninghami) which exhibited no temporal change. (2) Detections of almost all species were strongly related to the abundance of hollow-bearing trees. (3) Long-term declines in most species were associated with declines in hollow-bearing trees and temporal changes in stand age. And, (4) There were strong interspecific stand age effects, ranging from negative associations with young regenerated forest after wildfire in 2009 for the Southern Greater Glider (Petauroides volans), to positive associations with the same aged forest for the Common Ringtail Possum. Our findings underscore that forest management must properly address key drivers of decline. Management of montane ash forests must protect and promote the recruitment of large old hollow-bearing trees as a keystone resource for arboreal marsupials. Our results also highlight the substantial lag effects in forest condition resulting from past clearfelling and recurrent wildfires that has led to widespread forest degradation. Active, long-term forest restoration programs will be needed to address this problem.