TASMANIA IS missing a habitat, tall alpine herbfield, because of intense grazing by wallabies. On the mainland wallabies are kept at lower levels by heavy winter snow, and alpine herbfields are plentiful. But since 2011, with less snow on the mainland, wallabies are moving higher and this habitat is now at risk of being eaten.
Red-necked wallabies spell trouble for the vulnerable broad-toothed rat, which has an overlapping diet of grass. The two mammals seldom co-exist, suggesting that more wallabies in the Australian Alps will mean fewer broad-toothed rats. The Alps, extending from northern Victoria into southern NSW, are a stronghold for these rodents, which are missing from Tasmania’s uplands, except for the few sites where wallabies are kept out by boulders or prickly shrubs.
Because of Bennett’s wallabies, Tasmania has marsupial lawns instead of herbfields. (Image Credit: Bjørn Christian Tørrissen/Wikimedia)
Kookaburras are also reaching higher altitudes, where the endangered Guthega skink fails to recognise them as predators. At special risk are the pregnant lizards that bask for long stretches to hasten embryo development. The Australian government lists kookaburras as one of the threats to this species.
Introduced foxes, cats, rabbits and feral horses are also moving higher, to the detriment of wildlife. Yarrow, white clover and other weeds are expected further upslope as snow declines. Snow gums aren’t showing much sign of spread, but when they do, alpine herbfields and shrublands will be shaded out.
In talk about climate change, the movement of native species upslope and southwards is usually portrayed as desirable, as helpful to their survival in a changing world. Yet Australia has vast numbers of uncommon animals and plants living at high altitudes, at risk from common species invading their domain, as well as from climate change. This holds true right along the Great Dividing Range and in other mountainous regions as well.
In Tasmania one concern is that upland conifers will die from flammable shrubs that spread higher and promote fires. The common species heading upslope are not thought to face a serious problem from climate change, whether they move or not.
In any new discipline – such as climate change biology – the thinking evolves as evidence grows. Some upslope movements aren’t troubling, but even so, the default assumption that movement is good needs rethinking.