Consequences of the reintroduction of regionally extinct mammals for vegetation composition and structure at two established reintroduction sites in semi‐arid Australia

Abstract

Australia has lost a substantial proportion of its small to medium‐sized mammals since European colonisation. Given the passage of time since local extinctions – decades to more than a century for much of the continent – the consequences of these changes for vegetation are poorly known. In this study, we take advantage of two well‐established mammal reintroduction projects in southern inland Australia to examine the ecological consequences for vegetation of re‐established mammal populations. The study is based on replicated surveys inside and outside fenced reintroduction sites, with treatments characterised by varying presence, absence and composition of reintroduced mammals, feral predators and feral herbivores. We found a suite of differences in vegetation between reintroduction sites and matched controls, with generally lower richness inside reintroduction sites (with one exception). Other compositional differences varied by location, with some functional groups – herbaceous chenopods, shrubby chenopods, introduced geophytes and low shrubs – and a few individual chenopod species – being less frequent inside the reintroduction site at one location. At the same site, mistletoes and orchids were less abundant inside than outside the reintroduction site. Structural differences included a higher percentage of bare ground inside, and a higher ground layer for one inside treatment versus outside. Although the absence of baseline data and replicated temporal data limits inference as to causal factors, many of the results are consistent with data from other reintroduction sites. Some results, especially those for geophytes, mistletoes and some chenopods, may indicate long‐term consequences for those taxa. Whilst predator‐fencing substantially contributes to prevention of extinction of highly threatened mammals, some environmental trade‐offs are inevitable. Nonetheless, given the aims of reintroductions include re‐constructing natural ecosystem processes, the resulting changes to vegetation require ongoing investigation and further monitoring.

An assessment of potential herbivory impacts of a reintroduced marsupial in a predator‐free woodland sanctuary

“…of Ngaluda. Our assessment highlights the impacts of both Ngaluda in concert with Baray, and of Ngaluda on its own, which is consistent with the negative effects of overabundant herbivores generally, and reintroduced digging marsupials on native vegetation observed in other Australian sanctuaries specifically (Verdon et al 2016;Linley et al 2017;Moseby et al 2018;Kemp et al 2021;Michael et al 2022).…”

“…However, fenced sanctuaries are prone to ecosystem imbalance due to the absence of predators and competitors and the resulting overabundance of herbivores (Verdon et al 2016;Linley et al 2017;Moseby et al 2018). For example, the successful reintroduction of digging marsupials (such as the Burrowing Bettong Bettongia lesuer and Bilby Macrotis lagotis) across multiple sanctuaries in semi-arid Australia has been associated with decreases in floristic values and vegetation condition, including lower plant species diversity, reduced frequency of important functional plant groups, and declines in seedling abundance and survival (Verdon et al 2016;Linley et al 2017;Moseby et al 2018;Kemp et al 2021;Michael et al 2022). Ecologically, this is analogous to the predictable impacts of abundant large herbivores anywhere apex predators have been extirpated (e.g., Kangaroos Macropus spp.…”

Bringing back the endangered bridled nail-tailed wallaby at Taunton National Park (Scientific) through effective predator control

“…Predator-proof fencing is a rapidly expanding conservation action aimed at stopping the influx of introduced predators (Dickman 2012;Hayward and Somers 2012;Legge et al 2018;Berry et al 2019). However, poorly designed and planned fences, particularly those that contain species well outside their known range or climate change-affected range, could potentially do more harm than good and some of the concerns with predator-exclusion fences have been discussed elsewhere (Hayward and Kerley 2009;Legge et al 2018;Berry et al 2019;Roshier et al 2020;Kemp et al 2021).…”