The end of the line? Sandalwood surveying on Bon Bon Reserve
For National Tree Day, Richard McLellan takes us into the South Australian outback for a sandalwood survey, exploring the significance of the species and its unfortunate plight.
I am a PhD student at the University of New South Wales investigating the indirect top-down effects of the absence of dingoes on ecosystems. One of my study sites includes Boolcoomatta Reserve west of Broken Hill in South Australia. One aspect I am particularly interested in is the impact of a release in predation pressure from dingoes on kangaroos.
Kangaroos, when left uncontrolled, can proliferate in high numbers, which often leads to unwanted effects on our delicate dryland ecosystems.
Kangaroos feed mainly on grass and can deplete grass stocks when they're in unusually high numbers. Such a depletion in grass stocks can have an impact on other species that depend on this resource for food or shelter. This includes termites, which are a crucial component in the food chains of Australia’s arid ecosystems – serving as prey for a host of reptile and small mammal species.
Termites you say? Don’t they mostly feed on wood? Well, contrary to common knowledge, termites feed on a variety of resources including grass. As grass stocks are depleted by large herbivores, such as kangaroos, termites could be negatively impacted as well.
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Harvester termites collecting their dried veg in the morning.
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Female Crimson Chat on its nest
On Boolcoomatta, four sets of experimental kangaroo exclosures, each covering 1 hectare, gave me a unique opportunity to study the impact of kangaroo grazing on other organisms such as termites.
My first trip to Boolcoomatta was in November 2019 when I witnessed it at its driest and quietest (i.e. I encountered very few of the small critters that I’m keen to study). I then came back in July this year when a few green shoots were popping up here and there and finally came back in November this year and it was unrecognizable! Flocks of budgies everywhere, Crimson Chats all over the saltbush plains and herds of emus wandering at every corner.
A noticeable absence after this rain was the grass though, most of the green vegetation popping up was little forbs, which makes you wonder, where is the grass? Have the overabundant kangaroos made such a huge dent in its stocks that it would take longer for it to come back?
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Curl snake Suta suta in funnel trap
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Eastern hooded scaly foot Pygopus schraderi
While my first two trips showed that kangaroos impacted vegetation biomass and termite activity negatively, my trip in November aimed to go a level up the food chain and see if these differences had adverse effects on lizard and small mammal communities.
With financial support from the Nature Foundation SA, I was able to set traps in several of the exclosures and associated control areas nearby, using a variety of live trapping methods (e.g. Elliott traps, funnel traps and roof tiles placed in position as artificial habitat). While I was not expecting to catch much after two years of drought, I was positively surprised with the overall number of reptiles we caught.
Captures included skinks, legless lizards, snakes, frogs and even a little buttonquail that came back in our traps three nights in a row for a Michelin star meal of peanut butter!
It's currently too early to say if there's a difference in reptile and small mammal communities inside and outside the exclosures but I will be carrying out another survey in autumn next year to get a more definitive answer. Make sure to stay tuned for my next blog post to learn more!
