This article relates to the ongoing debate on Australian Rural & Regional News: Open for Debate: Koalas
Australian Rural & Regional News followed up with some further questions for Dr Brad Law, NSW DPI Principal Scientist, following this Koala update.
ARR.News: You say that “(a)nnual monitoring of koala occurrence in hinterland forests since 2015 has found a stable trend over time at a regional level.”
So, if koala numbers have been stable in the NSW hinterland forests – despite undoubted losses due to Black Summer fires – this must mean that koalas in the hinterland have increased in number, possibly substantially, since the fires – is this not so?
Dr Brad Law: We state that koala occurrence or site occupancy has been stable in hinterland forests of north-east NSW, which is not the same as koala numbers.
Stable occupancy of a metapopulation can include increasing and decreasing subpopulations, whereby connected populations that go extinct can be recolonised.
Where we have looked at koala numbers, such as at sites that burnt in the Black Summer fires, we clearly found a large reduction in numbers where moderate to high severity fire dominated. Generally, koalas persisted at most of these burnt sites, but their numbers were reduced.
ARR.News: Could this indicate that hinterland koalas are irrupting?
Dr Brad Law: We don’t have any evidence that koalas are irrupting, rather the metapopulation in north-east NSW has been stable in recent years.
ARR.News: You say that “(t)rend data are generally not available from other regions.”
So this means that there is no trend data showing that koala numbers have declined significantly (throughout NSW) over the last 5, 10 or 20 years?
Dr Brad Law: There is clear published data to show that the large koala population crashed in the Pilliga area because of drought and heat (Lunney et al. 2017) and there are also reports of declining numbers in the Liverpool Plains. There is some trend data available for coastal towns like Coffs Harbour where they appeared to be relatively stable (Lunney et al. 2016), but further north there is evidence of a decline at Iluka (Lunney et al. 2002). Elsewhere in NSW, there is limited solid data on koala trends.
ARR.News: You say,“These findings in no way suggest that concerns about the status of the koala in the wild are unfounded, or that they are not now absent, rare or declining in some areas.”
In what areas are koalas now absent, rare or declining and what is the evidence for that (given you have said that trend data are not generally available)?
Dr Brad Law: As stated above, the Pilliga population has crashed (Lunney et al. 2017). Other coastal populations have also been found to have declined (e.g. Lunney et al. 2002). By comparison, there is additional data available for south-east Queensland, indicating a declining trend (Rhodes 2015). Many areas of southern NSW support very low density populations of koalas, although this may be the natural situation in many of these remaining forests (Close et al. 2017).
ARR.News: You say that “habitat clearing, cars and roads, dogs, disease and fire are demonstrated, well-known threats to the koala.”
However, might not koala disease and mortality due to road deaths and dog attacks be a symptom (or effect) of an irruption of koalas, for instance in areas with large amounts of young foliage, such as the hinterland after the Black Summer fires?
Dr Brad Law: There are likely to be complex causes behind koala disease and mortality, which at times might be density dependent.
We have found koala occupancy to be lower in private native forests where there is a greater extent of sealed roads in the neighbourhood (Law et al. 2022). While this pattern is a simple correlation, it is suggestive that koala occupancy is lower where there are more roads because of more cars, and potentially other associated factors like more people, dogs, traffic, etc. See also Lunney et al. (2022).
It does appear to be the case that nutrition is high in epicormic leaves produced after fire, and that koalas rapidly recolonise burnt areas if there is good connectivity with unburnt forest.
ARR.News: You say, “These new methods are now being rolled-out across the state as part of the Koala Strategy by the NSW Department of Planning and Environment.”
How long will it be before there is reliable evidence of koala numbers and trends in numbers across NSW?
Dr Brad Law: That is a good question, but it is not straightforward to provide reliable population numbers. The NSW government has invested in a large-scale base-line survey across the state that has just begun (NSW Department of Planning and Environment). Answers to this question should therefore begin emerging over the next few years.
Related story: Koala update: Brad Law
– Robert Close, Steven Ward, David Phalen; A dangerous idea: that Koala densities can be low without the populations being in danger. Australian Zoologist 1 June 2017; 38 (3): 272–280. doi: https://doi.org/10.7882/AZ.2015.001.
– Law, B., Kerr, I., Gonsalves, L., Brassil, T., Eichinski, P., Truskinger, A., & Roe, P. (2022). Mini-acoustic sensors reveal occupancy and threats to koalas Phascolarctos cinereus in private native forests. Journal of Applied Ecology, 59, 835– 846. https://doi.org/10.1111/1365-2664.14099
– Daniel Lunney, Lisa O’Neill, Alison Matthews, William B Sherwin. (2002) Modelling mammalian extinction and forecasting recovery: koalas at Iluka (NSW, Australia), Biological Conservation, 106, 101-113.
– Lunney Daniel, Predavec Martin, Sonawane Indrie, Kavanagh Rodney, Barrott-Brown George, Phillips Stephen, Callaghan John, Mitchell Dave, Parnaby Harry, Paull David C., Shannon Ian, Ellis Murray, Price Owen, Milledge David (2017) The remaining koalas (Phascolarctos cinereus) of the Pilliga forests, north-west New South Wales: refugial persistence or a population on the road to extinction?. Pacific Conservation Biology 23, 277-294.
– Lunney Daniel, Predavec Martin, Miller Indrie, Shannon Ian, Fisher Mark, Moon Chris, Matthews Alison, Turbill John, Rhodes Jonathan R. (2016) Interpreting patterns of population change in koalas from long-term datasets in Coffs Harbour on the north coast of New South Wales. Australian Mammalogy 38, 29-43.
– Lunney Daniel, Predavec Martin, Sonawane Indrie, Moon Chris, Rhodes Jonathan R. (2022) Factors that drive koala roadkill: an analysis across multiple scales in New South Wales, Australia. Australian Mammalogy 44, 328-337.
– Rhodes, J. et al. South East Queensland Koala Population Modelling Study. UniQuest (2015)