Relationship between the common brushtail possum (Trichosurus vulpecula) and tuart (Eucalyptus gomphocephala) tree decline in Western Australia

Forest canopy loss due to plant pathogens, insect or abiotic factors significantly alters habitat and resource availability for animals, which has flow-on effects for whole ecosystems. The tuart (Eucalyptus gomphocephala) has been in decline throughout its geographic range; this is likely associated with watertable and salinity changes, although a plant pathogen (Phytophthora multivora) has also been implicated. We examined the relative abundance of common brushtail possums (Trichosurus vulpecula) across 12 sites (each 0.72 ha) selected on the basis of the health of dominant tuart trees (six ‘healthy’ and six ‘declining’ sites). Habitat variables (understorey, tuart dimensions and density, tree hollows, tree-to-trap distance) and tuart tree health (crown loss, epicormic regrowth) were compared with possum abundance. Possums were detected at most sites. There was no significant difference between brushtail possum numbers at ‘healthy’ or ‘declining’ sites, although marginally more possums were recorded at declining sites (5.7 ± 1.5 (s.e.), n = 6 sites) compared with healthy sites (3.3 ± 0.7; Cohen’s effect size d = 0.80). Slightly higher abundance of possums was associated with sites that had a greater density of smaller-diameter but taller tuart trees. ‘Declining’ sites, with more epicormic regrowth and greater tree densities, may provide more palatable food resources for possums.

The relationship between environmental variables, detection probability and site occupancy by Tasmanian nocturnal birds, including the Tasmanian masked owl (Tyto novaehollandiae castanops)

Knowledge of the habitat requirements of nocturnal birds is vital for the development of effective conservation strategies. This study is the first intensive systematic survey of the occurrence of the threatened Tasmanian masked owl (Tyto novaehollandiae castanops), the Tasmanian boobook (Ninox leucopsis) and the Australian owlet-nightjar (Aegotheles cristatus) in Tasmania using call playback, spotlighting and listening techniques. Occupancy models were created that explain the spatial distribution of the three species. Temperature and wind influenced the detectability of all species. Detectability of the Tasmanian boobook was also associated with nightlight. The Tasmanian masked owl was most often found in low-elevation mature dry eucalypt forest. This may be related to a combination of availability of nesting sites, food availability and accessibility, and physiological factors. The Australian owlet-nightjar also showed a broad preference for dry eucalypt forest and avoided open country. In contrast, the Tasmanian boobook was most often found in wet eucalypt forest with higher temperatures and fewer roads. We conclude that mature dry and wet forest types at low elevations need to be carefully managed to maintain populations of Tasmania’s nocturnal birds, particularly the threatened Tasmanian masked owl. Consideration should be given to retention of a network of contiguous areas of undisturbed mature forest across forested landscapes.

Does woodland condition influence the diversity and abundance of small mammal communities?

Loss of mammal species in Australia in the last 200 years has been attributed to many factors including habitat removal and altered fire regimes. Decline in tree condition could contribute further to the ongoing decline of mammals. Eucalyptus wandoo trees are currently undergoing a decline in condition that can result in a loss of canopy and other changes to the habitat. This paper examines the relationships between E. wandoo tree condition, habitat characteristics and small mammal species richness and abundance. Live-capture trapping was conducted at 24 E. wandoo sites at Dryandra State Forest and Wandoo Conservation Park, Western Australia. Condition and microhabitat variables of E. wandoo were recorded for each site. Generalised additive mixed models revealed a range of habitat and tree condition characteristics that influenced small mammal abundance and species richness, including site litter cover, crown dieback, understorey vegetation cover and tree density. The availability of coarse woody debris played a large role in explaining the abundance of Cercartetus concinnus and Antechinus flavipes, along with other microhabitat and tree condition variables, such as tree leaf litter and crown dieback. Epicormic growth, crown density and the distance to the drift fence from E. wandoo trees were the common variables in the best model for the abundance of Sminthopsis griseoventer. The decline in condition of E. wandoo and the subsequent modifications to the microhabitat are correlated with changes in the small mammal community. A better understanding of how the decline of E. wandoo impacts small mammal communities could improve management practices in E. wandoo woodlands.

The use of hollow-bearing trees retained in multi-aged regenerating production forest by the Tasmanian common brushtail possum (Trichosurus vulpecula fuliginosus)

Context Hollow-bearing trees are frequently retained in timber-production areas as part of measures to mitigate against the impacts of forest harvesting on fauna, yet few studies have investigated the effectiveness of such measures. Such studies are essential for adaptive forest management. Aims The main aim of the present study was to evaluate the use of hollow-bearing trees retained in harvested and unharvested forest as den sites by the Tasmanian common brushtail possum. In particular, we examined the distribution and types of hollow-bearing trees used as den sites and whether or not their use in harvested sites was influenced by time since harvest. Methods Thirty brushtail possums were radio-tracked to their day-time den sites between March 2007–July 2007 and July 2008–October 2008, at five dry Eucalyptus forest sites (three regenerating after partial harvest with hollow-bearing trees retained inside the coupe and two in relatively undisturbed forest) in south-eastern Tasmania, Australia. Key results The brushtail possums tracked in the study denned primarily in hollow-bearing trees at both the harvested and unharvested sites. At sites regenerating 8 and 10 years after harvest, most den site locations were in trees retained outside the harvest area, in large patches. In contrast, at the site regenerating 17 years after harvest, isolated trees and small patches within the harvested area were used. Conclusions Hollow-bearing trees retained within harvest areas do provide habitat for hollow-dependent fauna such as the common brushtail possum and enable recolonisation of harvested areas in the medium term. However, in the short term these trees may not be used and hollow-bearing trees retained in the surrounding landscape are important for providing refuge as the harvested area regenerates. Implications The retention of hollow-bearing trees in harvested areas may be an effective measure at enabling recolonisation of harvested areas once suitable habitat regenerates, but it is also important to ensure that large patches of mature forest (containing hollows) are retained in the surrounding landscape to ensure the persistence of hollow-using fauna.