Effects of feral free‐roaming horses on semi‐arid rangeland ecosystems: an example from the sagebrush steppe

Abstract

Abstract. Feral horses (Equus caballus) are viewed as a symbol of freedom and power; however, they are also a relatively unmanaged, non-native grazer in North America, South America, and Australia. Information about their influence on vegetation and soil characteristics in semi-arid rangelands has been limited by confounding effects of cattle (Bos taurus) grazing and a lack of empirical manipulative studies. We compared vegetation and soil surface characteristics in feral horse grazed areas and ungrazed exclosures at five sagebrush (Artemisia) steppe sites in northern Nevada. Horse grazed areas had lower sagebrush density and plant diversity, greater soil penetration resistance, and lower soil aggregate stability than ungrazed areas. Herbaceous cover and density generally did not differ between grazed and ungrazed treatments, with the exception of heavily grazed sites in which perennial grass cover was reduced. The cumulative effect of feral horses on soil characteristics suggests that they may affect the ecological function of semi-arid rangelands by increasing the risk of soil erosion and potentially decreasing availability of water for plant growth. The two-fold increase in sagebrush density with horse exclusion suggests that feral horses may limit sagebrush recruitment and thereby negatively impact Greater Sage-grouse (Centrocercus urophasianus) and other sagebrush associated wildlife. The effects of feral horses on sagebrush and other semi-arid ecosystems should be considered when developing conservation plans for these ecosystems and associated wildlife.

Feral horses influence both spatial and temporal patterns of water use by native ungulates in a semi‐arid environment

“…Increased numbers of horses are associated with negative impacts to arid and semi‐arid landscapes and some of the species inhabiting these environments (Beever , Beever and Aldridge , Davies et al. , Hall et al. ).…”

“…Increased numbers of horses are associated with negative impacts to arid and semi-arid landscapes and some of the species inhabiting these environments (Beever 2003, Beever and Aldridge 2011, Davies et al 2014, Hall et al 2016b). Horses can degrade habitat features (e.g., soil and vegetation) via trampling, excessive nutrient deposition, and overgrazing (Loydi and Zalba 2009, de Villalobos et al 2011, Parvage et al 2011.…”

Current reclamation practices after oil and gas development do not speed up succession or plant community recovery in big sagebrush ecosystems in Wyoming

“…Cattle are currently grazed at a fairly low stocking rate in the area, but feral horses are present in fluctuating abundance due to sustained population growth with periodic round‐ups as mandated by federal law (Public Rangelands Improvement Act ). Feral horses have been linked to a variety of negative effects on ecosystems (Davies et al ), and their apparent preference for certain wellpads in the area of our study may have prevented reclamation success or slowed successional processes.…”

Impacts of horse grazing on botanical composition and diversity in different types of heathland

“…Other studies have also found positive effects of horse grazing on floristic diversity in different plant communities like coastal and wet grasslands in France (Loucougaray et al 2004;Marion et al 2010). However, horse grazing can have negative impacts on plant diversity under more arid conditions, as found in rangelands in Nevada (Beever and Brussard 2000;Davies et al 2014). Greater increases in species density under horse grazing were found at 25-m 2 than at 1-m 2 quadrats.…”