Distribution and abundance of hollow-bearing trees in urban forest fragments

Habitat structures, such as hollow-bearing (i.e. cavity-bearing) trees, are globally recognised as important forest features for wildlife conservation and for providing important structural heterogeneity in natural and modified landscapes. The depletion of structural resources, such as hollow-bearing trees, within a landscape, may therefore be limiting to biota where no other functional substitutes exist. We surveyed 45 natural forest remnants across the rapidly urbanising City of Gold Coast, south-east Queensland, Australia to quantify the distribution and abundance of hollow-bearing trees. Tree and tree-hollow variables were quantified within the selected 91 plots. In total 6048 trees from 34 eucalypt species were sampled and 916 hollow-bearing trees containing 2159 hollows were recorded. The average hollow-bearing tree density (37.5 ± 3.13/ha) was much higher than those found in other studies within Australia. Hollows were more prevalent in large trees and the majority (50.4%) of hollows were bayonets (10 cm). Dead and decaying trees also had a greater likelihood of having a hollow than healthy trees. Our results highlight the value of urban forest remnants in maintaining the functional capacity of urban landscapes for biodiversity by protecting hollow-bearing trees as habitat resources. This information will assist conservation managers and planners to establish sound adaptive management plans to conserve biodiversity and ecosystem function in natural and modified landscapes.