As ecologist Mike Letnic trudged up and down the red-orange dunes of the Strzelecki Desert in South Australia, he noticed that his boots sank deep into the sand and his equipment was more likely to be covered in sand when he was on the northern side of what’s known as the Dingo Fence. A 5,614-kilometer barrier, the fence stretches across southeastern Australia and protects sheep flocks from the wild dogs—dingoes are plentiful on the north side of the fence, but very few exist on the southern side.
The contrast intrigued Letnic, a professor at the University of New South Wales’s Centre for Ecosystem Science, and he has dedicated many of his years to studying how the fence and the resulting lack of dingoes on the southern side have affected the desert’s ecosystem. He has documented, for example, how the absence of the large predator has allowed populations of feral cats and foxes to explode, which, in turn, has decimated the native herbivore populations. One such creature is the hopping mouse, which eats the seeds and seedlings of the native shrubbery. In a 2018 study, Letnic and a coauthor flew drones over the dunes and found that the dingoes’ absence on the southern side had allowed shrubs to grow more densely, which altered the dunes’ shape and size. The denser shrub coverage slows the velocity of the wind at ground level and causes the dunes to become taller and the sand to be more compact. “It’s a very windy place,” Letnic said. “And once the shrubs get to a certain density, the wind actually skates across the top of the shrubs.”
Abundant Kangaroos Gobble Up Grass
Letnic’s new study shows that the fence has also caused a different vegetation change—one that is so pronounced it can be seen from space. Using 32 years’ worth of satellite imagery, Letnic and Adrian Fisher, a remote sensing specialist at the University of New South Wales, found that native grasses on the southern side had poorer long-term growth than vegetation on the northern side.
The reason stems from the overabundance of kangaroos on the southern side (kangaroos are the preferred prey of dingoes), which has put tremendous grazing pressure on the native grasses. Letnic and Fisher compared the satellite images with weather data and found that after rainfall, vegetation grew on both sides of the fence, but it did not grow as much or cover more land on the southern side.
“It’s a desert, so there’s not much growth in plants. And then it will rain occasionally, and you get a lot of growth, and that’s when we were able to see the difference in the grazing pressure on each side of the fence,” said Fisher.
Reminder of the Past Landscape
Most dingo research has been conducted using either drone imagery or field studies, but the U.S. Geological Survey Landsat program has allowed for further analyses. A NASA satellite has been taking continuous images of the area since 1988. Satellite imagery, often used for crop or forest studies, traditionally looks strictly at photosynthesizing vegetation, such as plants, trees, and grass. Here Fisher used a model to factor in nongreen vegetation, like shrubs, dry grasses, twigs, branches, and leaf litter. According to Fisher, considering nongreen vegetation was necessary for an arid ecosystem. “Australia is mostly desert, and so to look at all that landscape, we need a good way to factor in the brown vegetation, the dry stuff,” he said.
The dynamics of how humans alter the food webs of ecosystems is an urgent topic and one that’s becoming even more difficult to predict because of climate change, says Sinéad Crotty, an ecologist and project manager at the Yale Carbon Containment Lab who was not involved in the new study. Letnic and Fisher, she said, “do a great job of utilizing multiple lines of evidence across spatial scales to demonstrate the effect of removing apex predators on vegetation and geomorphology.”
Letnic and Fisher said their work is an important reminder of how the area’s ecosystem used to be—one that’s easy to overlook because the fence has been around since the 1880s. “In Australia, we’ve been pretty successful at suppressing dingo numbers for more than 100 years,” said Letnic. “And that memory of what it was like before is nearly gone.”
—Nancy Averett (@nancyaverett), Science Writer
Averett, N. (2021), A reminder of a desert’s past, before dingo removal, Eos, 102, https://doi.org/10.1029/2021EO156969. Published on 08 April 2021.
Text © 2021. The authors. CC BY-NC-ND 3.0
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