Signals of change in tropical savanna woodland vertebrate fauna 5 years after cessation of livestock grazing

Abstract

Context There is growing evidence that vertebrates inhabiting the extensive savannas of northern Australia are undergoing a widespread decline as a result of the effects of anthropogenic land management such as the grazing of domestic stock. Despite the ubiquity of pastoral grazing in the Australian savannas, few studies have examined the changes in terrestrial vertebrate fauna following destocking. Aims The present study monitored the response of birds, mammals and reptiles to destocking of a newly acquired conservation reserve in north-eastern Australia. Methods The vertebrate fauna was sampled over a 5-year period. Standardised 1-ha survey was conducted twice a year in 2006, 2007 and 2010, at 40 sites representing six habitat types. Key results The fauna assemblage, the abundance and richness of major taxa, and the abundance of a suite of individual species were found to vary significantly with time since destocking. Although some of the observed trends were consistent with previously reported responses of vertebrates to grazing, in general species richness and abundance did not increase linearly over time since destocking, with an overall decline in the first year, and an increase in the subsequent survey. Mammals remained at very low abundance and displayed a trend contrary to that for birds and reptiles, and variation was often confounded by habitat type. Conclusions In general, where there has been a long history of pastoral land management, destocking alone may not induce short-term increases in the vertebrate fauna thought to be affected by grazing in Australian savannas. Implications Monitoring the outcomes of conservation management activity is a critical component of understanding the success, failures and adaptation needed to maximise the costs and benefits of conservation investment. The recovery of the vertebrate fauna thought to be of conservation concern in relatively intensively used, long-grazed landscapes may be lengthy and contingent on other factors, such as periods of favourable weather, or understanding the interactive effects of herbivore removal, fire pattern and feral predators. In such landscapes, it is possible that recovery of some elements of the vertebrate fauna may not occur without deliberate interventions, such as reintroductions or intense predator control.