The short term effect of fire severity on arboreal mammals

Fire severity and frequency is predicted to increase in Australia’s temperate forests over the remainder of the 21st century. With Australia’s history of mass mammalian extinctions, and with 25% of arboreal mammal species currently listed as threatened Australia wide, developing a greater understanding on the effect of fire severity on mammals is essential for effective conservation management. Detectability of arboreal mammals from popular survey techniques such as spotlighting is typically low, even for large bodied arboreal mammals, i.e., greater gliders (Petauroides volans). Methods that deal with imperfect detectability, typically perform better, and produce accurate estimates of species population size and distributions. Distance sampling is a form of population size estimation that accounts for detectability as a function of distance from a transect line. Occupancy modelling differs from distance sampling as it accounts for detectability by calculating a species’ redetections in repeat visits to a site. In this thesis we explored the short-term (\u3c 1 year) effect of fire severity on forest dependant arboreal mammal species at Monga National Park (MNP), NSW, using both occupancy modelling and distance sampling. We explored this with two objectives, firstly using occupancy modelling and secondly through distance sampling analysis. Three fire severity classes were investigated: low (canopy unburnt), moderate (partial canopy burn) and high (complete canopy consumption). Five sites, visited on three separate occasions, were surveyed within each severity class. To determine habitat preferences in arboreal mammal species, additional site covariates were recorded at each site. Spotlighting on off-track transects at each site was then completed over a four-week period. Objective one used occupancy modelling analysis to determine the effect of fire severity, and other habitat covariates, on arboreal mammals, whilst closely examining the effects on iii greater gliders and common brushtail possums (Trichosurus vulpecula). In general, fire severity influenced arboreal mammal occupancy. Fire severity, elevation, and dominant tree species had the largest influence on the occupancy of greater gliders, with occupancy highest in moderate fire severity sites. Additionally, greater gliders showed habitat preferences to high elevation sites dominated by brown barrel (Eucalyptus fastigata). Fire severity had a negligible effect on the occupancy of brushtail possums, instead slope and elevation had the largest influence with brushtail possums showing a habitat preference for steep sites in low elevations. Objective two used distance sampling to estimate the density of greater gliders at differing fire severity classes, using the surveys mentioned above. A global density estimates of 0.429 ha-1 (95% confidence interval (CI) 0.256-0.718 ha-1 ) was found, which varied according to fire severity classes; low 0.747 ha-1 (95 % CI 0.344-1.621 ha-1 ), moderate 0.515 ha-1 (95 % CI 0.285-0.932 ha-1 ), and high 0.071 ha-1 (95% CI 0.012-0.395 ha-1 ). The number of greater glider observations were significantly (p\u3c0.05) higher in low and moderate sites compared with high fire severity sites. The availability of tree habitat hollows was highest in low sites, however, were significantly lower in moderate severity sites. The key findings of this study indicate the importance of fire severity in determining the occupancy of arboreal mammals within a year since wildfire. A particularly interesting finding was the higher greater glider occupancy found in moderate severity sites, yet lower densities, compared to low severity sites. This could be potentially due to the increased food resource availability, as greater gliders prefer young new leaves that contain fewer secondary metabolites. This thesis highlights the importance of collecting baseline data on post-fire response of arboreal mammal to implement informed conservation management decisions