LAST year koalas from NSW, Queensland and the ACT were listed as ‘‘vulnerable’’ under the Commonwealth Government Environmental Protection and Biodiversity Conservation Act. This followed massive declines in the number and distribution of koala populations.
The main threat to koalas is loss of habitat.
Koalas mostly live on private land – land used by us humans too. Hence there is an immediate conflict between human needs for living and work space and the koalas’ need for trees.
The loss of habitat is exacerbated by deaths from road traffic and attacks from dogs.
If this isn’t enough, the small, stressed populations of koalas are threatened by diseases such as chlamydia.
Surprisingly – against the odds – the koala figures did show some populations that appeared to have increased in number. One of these was from the Liverpool Plains, surrounding the town of Gunnedah.
This area had been subjected to a large-scale tree-planting campaign in the 1990s to combat rising salinity and soil erosion. Our team of researchers from the University of Sydney and the NSW Department of Environment, Climate Change and Water (now the Office of Environment and Heritage), aided by the community-driven Liverpool Plains Land Management Inc and Foundation for National Parks, decided to investigate if the tree plantings were the reason for the increase in koalas.
We wanted to discover what lessons could be learnt from this landscape management.
We fitted 40 koalas with portable GPS units, attached to collars. These let us know where the koalas were every four hours. We could then follow the path of each koala to measure what tree they had been in.
Our results provided some new insights on how koalas use the landscape. The koalas used very different trees during day and night, and different trees as temperatures became hotter.
Koalas must balance their needs for food, water and shelter. Unfortunately these requirements often come from different trees.
Koalas eat only eucalyptus leaves, and only from certain species. The problem is that eucalyptus leaves are full of toxins and tannins, making it difficult for the koalas to extract their required nutrients. Hence koalas need to feed from a number of different trees to balance their nutrients and toxin levels.
Then koalas need a place to rest out of the heat. They don’t burrow or fly, so they need to find the appropriate trees to find respite from the sun.
This leads us to our findings.
Koalas during the day, and at warmer temperatures, used larger trees with more shelter and in gullies. These were often non-eucalyptus trees like belah and kurrajong. The koalas had to sacrifice feeding in their favourite trees in the area, such as river red gums and bimble box, to find trees to protect them from the heat.
The cost for those koalas not having access to these shelter trees was potentially enormous. In 2009, a week-long heatwave of temperatures above 40 degrees Celsius caused about a quarter of the population to perish.
So what are the lessons from this study for the conservation of koalas in the long term?
The focus of much planning for koalas has been on their food trees. Our study clearly shows that shelter trees are just as important for maintaining viable koala populations.
As many of these shelter trees were larger, and trees don’t grow overnight, it also demonstrates that we need to maintain larger older trees, as well as planting new trees, to conserve koala populations. This is particularly important as heatwaves like the one in 2009, are expected to increase in frequency and intensity into the future.
However it is not all doom and gloom. Our study shows how scientists, government agencies and farmers can all work together in the conservation of a species.
Koalas like trees on fertile soil, and hence they are often on private farming land. The farmers of the Liverpool Plains, aided by Liverpool Plains Land Management Inc, have enabled both the conservation of koalas on their land and have assisted the current research.
If we pay attention to this research, we can both plant and maintain trees, and therefore maintain koala populations way into the future.
We still need to know more about how koalas choose trees, particularly how they can balance nutrients and toxins, and that relies on continuing research.
There is a decline in biodiversity researchers and their funding, which will make conservation projects even more difficult in the future.
Conservation and research need to work hand in hand, or irreversible mistakes can be made. We are very grateful for the support of the funding bodies, and the support of the University of Sydney.
Dr Mathew Crowther is senior lecturer in the School of Biological Sciences at Sydney University.
NEEDING SUPPORT: While their numbers have increased, koalas are listed as vulnerable in two states and the ACT.