Australian research
Australian literature generally concludes that Brumbies cause damage to the environment but these studies are based on correlative data and weak inferences that actually contain evidence supporting the belief that horses can have positive environmental impact.
This positive ecological impact is rarely if ever acknowledged because of the strong belief of Australian environmentalists, that since horses are introduced, heavy hard hoofed animals they must only cause damage in Australia.
ABA Research on Density-Impact of Horses in Victoria
The published Wildlife Biology paper Use of density-impact functions to inform and improve the environmental outcomes of feral horse management (Berman, et al, 2023) presents a new approach to studying the environmental impacts of wild horse in the environment.
The premise of this study is that to better manage horses (or any species) on the land, we need to first “….understand the relationship between horse density and environmental impact”.
Think of it like this: how much environmental impact is made by 5 horses in a square kilometer versus 10 horses?
The study was conducted in the Bogong High Plains and the Eastern Australian Alps. In both areas, it was found that there was a threshold limit of horse density below which negligible environmental impact was detected, however, above the limit, environmental impacts increased exponentially.
This finding strongly suggests that management programs would be most cost effective by targeting areas where horse density was above the threshold for a particular area. Conversely, horse control programs in areas where density is below this threshold do little or nothing to improve the environment.
You can view or download the full paper and a summary of the study via the links below
Wild Equine Research Around the World
Examples of research demonstrating positive impacts of wild horses are presented below.
References
Austrheim, Gunnar and Eriksson, Ove, 2001, Plant species diversity and grazing in the Scandinavian mountains – patterns and processes at different spatial scales, Ecography 24: 683-695, Copenhagen 2001
Beavis, Sara, 2002, Horse Riding in Kosciuszko National Park, A report to Snowy Mountains Horse Riders Association, Centre for Resource and Environmental Studies, Australian National University, Canberra
Beever, Erik, 2003, Management Implications of the Ecology of Free-Roaming Horses in Semi-Arid Ecosystems of the Western United States, Wildlife Society Bulletin (1973-2006) Vol. 31, No. 3 (Autumn, 2003), pp. 887-895 (9 pages)
Beever, E.A. and Herrick, J.E. , 2006, Effects of feral horses in Great Basin landscapes on soils and ants: Direct and indirect mechanisms, Journal of Arid Environments Volume 66, Issue 1, July 2006, Pages 96-112
Colloff, Matthew J., et al., 2013, Ecology and conservation of grassy wetlands dominated by spiny mud grass Pseudoraphis spinescens in the southern Murray–Darling Basin, Australia, Aquatic Conserv: Mar. Freshw. Ecosyst. 24: 238–255 (2014) Published online 13 September 2013 in Wiley Online Library
Connell, Joseph H., 1978, Diversity in Tropical Rain Forests and coral Reefs, Science, New Series, Vol. 199, No. 4335 (Mar. 24, 1978), pp. 1302-1310 (9 pages), American Association for the Advancement of Science
Davies, KW, Boyd, CS, Bates, JD and Hulet, A 2015, ‘Dormant season grazing may decrease wildfire probability by increasing fuel moisture and reducing fuel amount and continuity’, International Journal of Wildland Fire 24: 849–856.
Davis, et al. (2011), Don’t judge species on their origins, 9 June 2011, Vol 474, Naturue, pp 153-154
Dobbie et. al., 1993, Managing Vertebrate Pests: Feral Horses, Australian Government Publishing Service, Canberra
Fahnestock, J.T., Detling, J.K. The influence of herbivory on plant cover and species composition in the Pryor Mountain Wild Horse Range, USA. Plant Ecology 144, 145–157 (1999). https://doi.org/10.1023/A:1009899509067
Fahnestock, Jace T., and Detling, James, 2002, Bison Prairie Dog Plant Interactions in North American Mixed-grass Prairie, June 2002, Oecologia 132(1):86-95
Fortwangler, Crystal, 2013, Untangling Introduced and Invasive Animals, Environment and Society: Advances in Research 4 (2013): 41–59
Gilfedder, L., and Kirkpatrick, J.B., 1994, Climate, Grazing and Disturbance, and the Population Dynamics of Leucochrysum albicans at Ross, Tasmania, Australian Journal of Botany 42(4) 417 – 430
ITRG 2016, Final report of the Independent Technical Reference Group: Supplementary to the Kosciuszko National Park Wild Horse Management Plan, report by the Independent Technical Reference Group to the Office of Environment and Heritage NSW, Sydney.
Linkletter, Wayne L., et al.,2000, Social and spatial structure and range use by Kaimanawa wild horses (Equus caballus: Equidae), New Zealand Journal of Ecology (2000) 24(2): 139-152
Nimmo, Dale Graeme and Miller, Kelly K., 2007, Ecological and human dimensions of management of feral horses in Australia: a review, Wildlife Research, 2007, 34, 408–417, CSIRO Publishing
Ostermann-Kelm, Stacey D. et al., 2009, Impacts of feral horses on a desert environment, BMC Ecology 2009, 9:22, This article is available from: http://www.biomedcentral.com/1472-6785/9/22
Pickering, Catherine, et al., 2001, Estimating human-mediated dispersl of seeds witin an Australian protected area, August 2011 Biological Invasions 13(8):1869-1880 DOI: 10.1007/s10530-011-0006-y
Quinn, Adda, 2004, Environmental Aspects of Horses on Trails, American Trails website, https://www.americantrails.org/resources/environmental-aspects-of-horses-on-trails
Redfearn, Sally-Anne, et al., 2011, Detecting stream health impacts of horse riding and 4WD vehicle water crossings in South East Queensland: and event based assessment, Griffiths University October 2011
Rogers, G.M., 1991, Kaimanawa Feral Horses and their Environmental Impacts, New Zealand Journal of Ecology (1991) 15(1): 49-64
Schultz, Nick L., et al., 2011, Effects of grazing exclusion on plant species richnessand phytomass accumulation vary across a regionalproductivity gradient, Journal of Vegetation Science22(2011) 130–142
Silvers, L 1993, ‘The effects of grazing on fuel loads and vegetation in the Barmah Forest’, Honours thesis, School of Environmental and Information Sciences, Charles Sturt University, Albury, NSW.
Snowy Scientific Committee, 2008, Adequacy of environmental releases to the Snowy River, Report No. 1 Prepared for the Water Ministerial Administration Corporation, October 2008, Canberra
Stroh, Peter A., et al., 2012, The potential for endozoochorous dispersal of temperate fen plant species by free-roaming horses, Applied Vegetation Science Vol. 15, No. 3 (August 2012), pp. 359-368
Verbrugge, Laura, 2016, Metaphors in Invasion Biology: Implications for Risk Assessment and Management of Non-Native Species, September 2016 Ethics Policy & Environment 19(3):1-12
Williams, Richard, et al., 2014, Alpine ecosystems, in Biodiversity and Environmental Change (CSIRO Publishing, 2014)
Willig, M.R. , et al., 2018, Latitudinal Gradients of Biodiversity: Pattern, Process, Scale, and Synthesis, Annual Review of Ecology, Evolution, and Systematics Vol. 34:273-309 (Volume Publication date November 2003) First published online as a Review in Advance on July 11, 2003
Zalba, Sergio M., and Cozzani, Natalia C., 2004, The impact of feral horses on grassland bird communities in Argentina, Animal Conservation (2004)7, 35–44, The Zoological Society of London.