Impacts of feral horses and deer on an endangered woodland of Kosciuszko National Park

Abstract

Summary In recent years, the impacts of rapidly increasing populations of feral horses and deer on the vegetation and stability of soils have become highly visible and widespread in Kosciuszko National Park. We investigated these impacts in the White Cypress Pine (Callitris glaucophylla Joy Thomps. & L.A.S. Johnson) – White Box (Eucalyptus albens Benth) woodlands of the lower Snowy River valley. This woodland is a component of the White Box‐Yellow Box‐Blakely's Red Gum Grassy Woodland and Derived Native Grasslands complex that is nationally listed as a critically endangered ecological community. To investigate the severity of the impacts of feral horse (Equus caballus) and deer (Dama dama and Rusa unicolor) in the valley in 2013 and 2017/18, we surveyed fenced exclosures and paired grazed plots that were first established and surveyed in 1984 and re‐surveyed in 1987. Using LFA and VAST methodologies (not used in 1987), we compared the relative response of environmental variables in plots inside and outside the exclosures in an attempt to ascertain recent herbivore impacts. While there was no evidence of horses or deer from dung surveys in 1987, in 2018, 84% of the dung was from horses, 13% from deer, 1% from rabbits and 2% from macropods. Total herbivore dung density increased fourfold since the 1987 survey. On the understanding that all plots had the same starting condition in 1984 with respect to prior herbivory, we deduce that horses and deer are having significant ecological impacts. There was a far greater cover of understorey plants and the midstorey was denser and taller inside the exclosures. Outside the exclosures, the vegetation cover was far more sparse and soil erosion was active and extensive. The total number of invertebrates captured in small pitfall traps was nearly twice as many within the exclosures compared to the grazed plots. The dense even‐aged regrowth overstorey stands of White Cypress Pine, inside and outside the exclosures, have changed little in 34 years.

Impacts of feral horses in the Australian Alps and evidence‐based solutions

“…In southern Kosciuszko, invertebrate abundance was almost twice as high in fenced woodland plots compared with areas exposed to overgrazing (Ward‐Jones et al . ). By altering vegetation structure, feral horses also likely reduce the abundance of Alpine Water Skink ( Eulamprus kosciuskoi ) (Cherubin et al .…”

“…; Hope #11363;Ward‐Jones et al . ), frogs (Foster & Scheele ), fish (Allan & Lintermans ), reptiles and small mammals (Cherubin et al . ) all showed that feral horses were the sole or major cause of environmental damage across their study areas.…”

Lessons from old fenced plots: Eco‐cultural Impacts of feral ungulates and potential decline in sea‐level rise resilience of coastal floodplains in northern Australia

“…For example, in Kenya, ungulate grazing pressure had a significantly stronger effect on plant regeneration than rainfall (Muthoni, et al 2014). In Australia's Kosciusko National Park, exclusion fences demonstrated that horses and deer reduce soil stability, water infiltration capacity, nitrogen content, vegetation cover and height, and increase bare ground (Ward-Jones, et al 2019).…”

“…In Australia’s Kosciusko National Park, exclusion fences demonstrated that horses and deer reduce soil stability, water infiltration capacity, nitrogen content, vegetation cover and height, and increase bare ground (Ward‐Jones, et al . 2019).…”

Distribution, nature and threats to soils of the Australian Alps: A review

“…The negative impacts of feral horses have been well documented in both the NSW and Victorian Alps, and include erosion and pollution from trampling, pugging, grazing, track creation, collapsing stream banks and incision of wetlands and streams (Dyring 1990, 1992; Ward‐Jones et al . 2019; Dawson 2009; Dawson & Axford 2011; Wild & Poll 2012; Worboys & Pulsford 2013; Robertson et al . 2015; Tolsma & Shannon 2018; AAS 2018).…”