Exotic herbivores dominate Australian high‐elevation grasslands

Abstract

Invasive species are major drivers of ecosystem degradation globally. How invasive herbivore impacts differ from native herbivore impacts remains understudied. We examined the relationships between herbivore sign and vegetation height, foliage density, cover of forbs, weeds, bare ground, and soil compaction across environmental and herbivore activity gradients in the mainland Australian Alps. We detected native and exotic herbivore sign at 32.8% and 94.0% of sites, respectively. Total herbivore activity was primarily attributed to exotic herbivores and was associated with elevation and grassland type.Greater horse (exotic) activity was associated with lower vegetation height, lower foliage density, higher forb cover, and higher soil compaction. Greater rabbit and hare (exotic) activity was associated with lower vegetation height, lower foliage density, and a higher cover of bare ground. Greater total herbivore activity was associated with greater weed cover. Neither deer (exotic) nor kangaroo and wallaby (native) activity was related to response variables. We demonstrate that exotic herbivores dominate mammalian herbivory in these grasslands, which evolved without analogous hooved species. Given the restricted distribution and high endemism of these ecosystems, and associations between exotic herbivores and characteristics of degraded grasslands, we recommend landscape-scale exotic herbivore management, focusing on maintaining ground cover and vegetation structure.

Use of density‐impact functions to inform and improve the environmental outcomes of feral horse management

“…This view is clearly inconsistent with data that does account for sampling bias and detectability (Table 2–4, Fig. 2–5) and with the findings of a recent study in Kosciuszko National Park, adjacent to our study site (Hartley et al 2022). These results show clearly that in spite of deer and feral pig control and management of fire and human activity (Parks Victoria 2016, GSBMPWG 2020, Comte et al 2022), these combined impacts far exceed those impacts associated with the sign of feral horses.…”

Rare but not lost: Endemic mountain lizard occupancy following megafire and grazing disturbances

“…While livestock grazing is now limited to small areas of private property, grazing mammals on Kosciuszko Plateau are dominated by invasive species in terms of the number of taxa, area of occupancy and grazing intensity (Hartley et al, 2022). Invasive herbivores occupy the treeless vegetation communities across the plateau, including elevations >1500 where ecosystems evolved in the absence of extensive grazing by medium to large mammals (Costin et al, 1982; Hartley et al, 2022). Native grazers include the eastern grey kangaroo ( Macropus giganteus Shaw 1790), red‐necked wallaby ( Macropus rufogriseus Desmarest 1817), common wombat ( Vombatus ursinus Shaw 1800) and broad‐toothed rat ( Mastacomys fuscus Thomas 1882).…”

“…This finding is supported by long-term monitoring in Victoria that suggests the species is largely absent from areas with low, sparse vegetation and especially abundant in areas with dense ground stratum vegetation and few introduced grazers (N. Clemann, unpublished data, 2022). As sustained grazing by invasive species tends to reduce vegetation complexity on Kosciuszko Plateau (Hartley et al, 2022), we anticipate that prolonged, heavy grazing is likely to degrade ground stratum vegetation beyond a habitat suitability threshold for C. praealtus and subsequently reduce site occupancy, especially in periods of drought.…”

“…While there is limited research on the impacts of invasive herbivores on reptiles in the Australian Alps, previous studies have established that grazing degrades breeding habitat for threatened frog species (Foster & Scheele, 2019) and is implicated in the localized extirpation of a threatened rodent species (Schulz et al, 2019). Many reptile species are dependent on the specific vegetation structure of their specialized microhabitats, and grazing activity has been associated with changes in grassland characteristics, such as high weed cover, reduced ground stratum height and foliage density and increased bare ground (Hartley et al, 2022). Therefore, broadscale, prolonged or intense grazing by invasive herbivores is likely to be particularly detrimental to reptiles (Doherty et al, 2020; Kay et al, 2017) and, as invasive herbivore populations expand (Cairns & Robertson, 2015), an increasing threat to reptiles in the Australian Alps.…”

“…Cyclodomorphus praealtus may require targeted conservation action in response to fire events, due to its restricted range and the impacts of increasing fire frequency and invasive herbivores (Santos, Sitters, et al, 2022). Cyclodomorphus praealtus may be highly vulnerable to fire and prolonged grazing, as it relies on ground stratum vegetation complexity (Sato et al, 2014) and has not evolved in a fire‐prone or heavily grazed landscape (Ferreira et al, 2016; Hartley et al, 2022; Zylstra, 2006). Further, its slender body may make it prone to water loss in post‐fire conditions (Ferreira et al, 2016).…”