The only way is up: reptiles in trees resist the impacts of cattle grazing

With Reptile Awareness Day coming up, Heather Neilly comments on the effects of cattle grazing and her recent article, Arboreality increases reptile community resistance to disturbance from livestock grazing.

Grazing by domestic livestock occurs on 25% of Earth’s land surface. With such vast landscapes being used, it is important to understand how this land use affects the native wildlife in these areas.

We know that grazing can have major impacts on ground-level (terrestrial) habitat and the animals that live here, but how does it affect the habitat of tree-dwelling (arboreal) wildlife? At a global scale, grazing is implicated in the decline of many animal species. However, there are some species that appear to be resistant to the effects of grazing, either benefiting from the structural changes at ground level or avoiding them, as may be the case with arboreal species.

We set out to examine how different levels of grazing affect animal habitats, both on the ground and in the trees and to find out if arboreal reptiles were more resistant to heavy grazing compared with terrestrial reptiles.

Our research took place in northern Australia at ‘Wambiana’, a long-term cattle grazing trial in tropical savanna woodland. While cattle grazing in this area is extensive, trees at this site have not been cleared and the cattle graze on native grass. We surveyed the terrestrial and arboreal reptile community over two years, in four different grazing treatments. At the same time, we recorded how the structure of the ground and arboreal habitats were responding to the grazing treatments.

We found that habitat structure on the ground (e.g. grass, woody debris, leaf litter, small shrubs) were most affected by cattle grazing. Therefore it was the reptiles on ground that were negatively impacted by heavy grazing. These species relied on complex ground structures to find food, shelter and thermoregulate, and heavy grazing reduced this habitat. On the other hand, trees and other arboreal habitat (e.g. hollows, flaky bark) were not affected by grazing, and so reptiles in trees were able to thrive in all of the different grazing treatments.

Our findings help us understand how a reptile community responds to grazing and guide management decisions. While arboreal reptiles resisted the impact of grazing in our study, it is important to remember that our site had no tree clearing. Retaining trees in grazed landscapes provides important habitat for both arboreal and terrestrial wildlife.

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