On the environmental dynamics of forests, koala habitat and climate refugia in eastern Australia: a remote sensing approach

Abstract

Forests and woodlands are biodiverse treed ecosystems which grow in many different biomes across Earth from tropical lowlands of Papua to the semi-arid plains of central-eastern Australia. As climate extremes such as heatwaves and droughts are becoming longer and more intense, the responses of forests and woodlands are important for the suitability of animal habitats, in many environments. Folivores are herbivorous animals are dependent on the productivity of foliage which comprises their diet. Specialist herbivores that forage almost solely on the leaves of one genus or group of plants, specialist folivores like the koala (Phascolarctos cinereus), can also be dependent on foliar moisture. During extreme conditions, like hot droughts, foliar moisture content may limit capacity for thermoregulation and thus survival in specialist folivores, alongside a potential loss in energy intake with declining habitat productivity. Due to their reliance on foliar water in extreme conditions, koala distributions are linked to this variable, which can be remotely sensed. Furthermore, climate change means that conditions are becoming more common under which koalas’ need for water increases while the availability of water decreases. In this way, climate change may be rapidly altering the habitable range of this species and identifying refugia becomes ever more important. The demand of folivores for water under varying environmental conditions is better understood than the availability of these resources throughout forests and time. If we are to apply our understanding of the former to identify the magnitude of the threat to populations, we need to improve our understanding of the latter. In this thesis I aimed to investigate the effects of water availability and temperature on foliar moisture content and energy in eucalypt forests and woodlands at a range of temporal and spatial scales, using several different approaches. I primarily used reflectance data from the Sentinel-2 and Landsat satellites, and a spectrophotometer, to build spectral models of foliage response throughout ecosystems. The results of this thesis reveal the spatial and temporal variability in what is often assumed to be a static habitat characteristic. Foliar moisture is an important constraint on habitat quality and foraging preferences in hot drought. Another potential constraint on habitat quality, demonstrated in this research, is forage potential energy. The FMC modelling undertaken for this thesis produced a large timeseries dataset. This dataset will facilitate new knowledge in animal ecology through improved biophysical models by explicit estimation of microenvironmental conditions that limit folivore thermoregulation. The FMC dataset will also allow for improved analysis of fire risk and dieback effects within forests, both of which also have implications for koalas and other forest dependant fauna.

Date of Thesis submission	2024
Original language	English
Awarding Institution	Western Sydney University
Supervisor	Ben Moore (Supervisor), Kara N. Youngentob (Supervisor), Marta Yebra (Supervisor) & Mattias Boer (Supervisor)