LB 26-271 - Identifying habitat productivity thresholds for folivores using NDVI considering drought.

Background/Question/Methods:

Habitat suitability for herbivores may be altered by climate change as vegetation responds to extreme events. Predicting such vegetation response and the resulting potential habitat distribution could assist in the conservation of threatened species. Here, we studied potential koala habitat in eastern Australia and vegetation suitability in the form of a remotely sensed index of productivity, the normalised difference vegetation index (NDVI). Historically wide-ranging, the koala browses primarily on the foliage of eucalypt trees and is threatened directly but also indirectly by climate changes including altered drought frequency and severity. The Millennium Drought (2001-2009) in eastern Australia is one of the worst droughts on record. Using a large, long-term, ad-hoc koala presence dataset we identified the NDVI minimum at koala sites across time. We then compared this with minimum NDVI of koala landscapes before and during the drought period, and mapped suitability and changes between periods.

Results/Conclusions:

Our results show that minimum suitability thresholds derived from koala sites were considerably higher than landscape minima in drought or non-drought periods, for 3 vegetation groups. For instance, thresholds were 0.89 to 1.16 times the median of the landscape minimum NDVI. Prior to the drought, 42.3% of all vegetation was above thresholds (i.e. suitable, 211,215.2 km²). In the drought period, 17.8% of the area of unsuitable vegetation had previously been suitable (43,109.3 km²). This means that 242,054.4 km² of potential habitat are below the productivity niche observed for koala sites in general and likely have poor-quality forage (i.e. low energy and water). Conversely the vegetation which remained suitable in the drought period can be considered potential habitat under expected climate changes.