The Ecological Impact of Horses as a Keystone Species Critical to the Regeneration of the Earth

Dartmoor Ponies on Little Mis Tor

The Ecological Impact of Horses as a Keystone Species Critical to the Regeneration of the Earth

By Janice M. Ladendorf

For many years, the future of the feral horses who remain on public property in the United States has been highly controversial. Those who want to exterminate them have had considerable success. They believe horses damage the range environment, but instead modern scientific research has established they enhance it.

Conservation biologists have classified equines as one of the keystone species which is critically important in the regeneration of the Earth. Scientists believe evolution gave horses the ability to modify their environment to suit their species and in doing so, they will benefit numerous plants and animals who share their ecosystem. Rewilding or species reintroduction is increasingly being seen as a valuable tool for saving species from extinction and for reintroducing locally extinct species.

Equines have a favorable impact on their ecology because of their unusual digestive systems and free roaming habits. Their digestive systems are relatively inefficient so they must eat a high quantity of food to satisfy their nutritional needs. Horses prefer high quality grasses, like the gamma grasses our prairies once had, but evolution gave them the ability to survive on any type of grass, such as the low quality salt marsh grasses on Assateague Island. Wild horses will typically graze down lower quality grasses whose growth could otherwise feed forest fires. Horses are not just grazers; they are browsers who can digest plants, such as shrubs, leaves, shoots, and bark. They will even eat poison ivy and dandelions. In the winter, Indian ponies often survived because they could eat and digest cottonwood bark.

The end result of their high quantity diet is lots of quality manure. It includes the seeds of whatever wild plants they are eating and it enhances soil fertility because it contains a high level of nitrogen. As wild horses roam, they deposit manure all over their territories and it encourages the growth of vegetation. Some research has discovered horse-grazed sites show better grass cover and species richness. When they are fenced or held by humans in too small an area, they can damage their environment. So far, there is no proof free-roaming horses have ever damaged the ecology of their environment. On the contrary, if they are allowed to roam freely in enough space, they will enhance their environment. This fact has been well established in Eurasia, but ignored in the United States.


The Pleistocene Park in northern Siberia is an attempt to recreate the ecological system which once existed in Beringia, the land which once linked Siberia and Alaska. One of the first steps in this project was to select Yakut horses as the representative equines for the park. When they were turned loose in the park, some died because they could not tolerate the severe winters and others because they ate poisonous plants. Those who were left thrived and changed their environment. Mosses, weeds, and willow shrub have disappeared and they now graze on the grasslands they created.

Yakut horses in Pleistocene Park
Yakut horses in Pleistocene Park

Canada: Sable Island Wild Horses

This island lies off the coast of Nova Scotia. Despite the lack of predators, these horses have thrived since humans first abandoned them there in 1753. For a long time, the herds were frequently harvested and many were shipped off-island for sale on the mainland. Since 1961, Canadian law has protected these horses from humans. When the round ups were stopped, the horses adjusted to the change and the equine population remained relatively stable for many years. Recently it has increased, but the horses continue to thrive. No research has

The feral horses of Sable Island
The feral horses of Sable Island

been reported as to why this has happened. Like the Yakut ponies, they may have improved their environment so it can carry more horses. In 2011, Sable Island finally became a true nature preserve.


 In the European rewilding projects, certain breeds of small horses or ponies have been selected for reintroduction. Konik horses are a re-creation of one of the original types of wild horses. Many of the English pony breeds are semi-feral because they are allowed to roam freely on common pastures or preserves. As compared to most pampered domestic breeds, these ponies are more resistant to harsh weather and severe winter conditions. They are still adapted to foraging in the wild and capable of digesting coarse grasses and shrubs, as well as adjusting their diet according to the season of the year and food availability. Our American mustangs have the same capabilities.

Konik Horses

The first reintroduction project began in the Netherlands in the Oostvaardersplassen, a famous wetland which had been reclaimed from the sea. In 1984, Konik horses, Heck cattle, and red deer were introduced there to control the emerging forests and to keep open the areas needed by migrating birds. The first 20 ponies thrived and their number now exceeds 1,000. They proved to be hardier than the Heck cattle. The Konik or Konig is the result of an attempt to recreate the tarpan, the Heck cattle is the result of a similar attempt to recreate the aurochs.

Konik horses of Oostvaardersplassen
Konik horses of Oostvaardersplassen

Other projects in England soon followed the one in the Netherlands. One of the few remaining pieces of undrained fen in East Anglia is Wicken Fen. The project there carefully followed the World Conservation Union guidelines for the protection of the environment against invasive species, as well as the appropriate government regulations. In 2003, tough, robust Konik ponies and Highland cattle were introduced there. At both Oostvaardersplassen and Wicken Fen, administrators believe the creation of optimal environments requires the use of multiple species.

The horses at Wicken Fen began by carefully investigating every inch of the new land. Soon they established paths along favored routes, and started grazing evenly around their new territory. They eat lush, sweet grasses in the spring and summer; then add rushes and sedges in the autumn and winter. They regularly browse on scrub and plants, such as nettle, thistle, and bramble.

Konik horses are currently being used to manage four nature preserves in Kent at Stodmarsh, Pegwell Bay, Whitehall Meadows, and Ham Fen. At Stodmarsh the Koniks are rotated regularly among areas of marsh and reed bed. At the other preserves, Konik horses have been put out to graze by farmers and they helped speed the conversion of marginal farmland to grassland. Numerous species have benefited from these changes, including ducks, geese, and meadow birds.

Other English Pony Breeds

 The English may have begun with wetlands, but reintroduction soon spread to other types of terrain. In 1989, New Forest ponies were invited to graze on National Trust land in Hampshire, Wiltshire, and the Isle of Wight. Recently the town of New Milton invited six New Forest ponies to graze on Barton Common and put seven Dexter cattle out on Ballard Water Meadow. Experts expect to see a greater variety of dragonflies and hoverflies, as well as wetland and heath land plants. The town’s main goal was to improve the habitats for plants and wildlife; but in addition, they no longer had to pay to have the grass mechanically mowed.

One of the responsibilities of the Dartmoor Commoners Council is the ponies who graze on the moor. In recent years, their population has continued to decline and the council was concerned about the ecological impact on the moor. They commissioned a study relevant to pony grazing on upland habitats. They found some general guidelines, but concluded they needed to know much more about the ecological interaction of the ponies, cattle, and sheep who graze on the moor.

Dartmoor Ponies on Little Mis Tor
Dartmoor ponies on Little Mis Tor

Exmoor ponies have also turned out to be an excellent choice for conservation projects. They thrive on the low quality plants on chalk grassland and heath land because they are highly selective grazers who devour coarse grasses, gorse, rush, sedges, brambles, and even bracken. When they kept the grass short in Purbeck, Dorset, two rare species of orchids flowered once again. When they were released in the Quantock Hills in Somerset, violets returned to the tracks and the deer increased in number.

Much of the once rich and productive land now in the Czech Republic was badly damaged by the collectivization policies enforced from 1940-1989 by their communistic government. Environmentalists there have begun a large scale project to heal the land.  After careful investigation, they decided not to use Koniks because of genealogical errors made by the breeders who created them, so instead they decided on Exmoor ponies. Fourteen mares and a stallion have been shipped there from England. They were turned loose near Prague on land which had been barren for 70 years. The ponies have adapted well and numerous endangered plants and animals have started to return, much faster than the researchers expected.

The Future

The Netherlands proposes to turn 17 percent of their land into nature preserves. Their plans include the extension of preserves into Belgium and Germany.  The United Kingdom plans to continue turning marginal farming land into nature preserves. Tourism now accounts for ten percent of the world’s GNP and ecotourism has been a significant part of this increase. The Welsh are already thinking or reintroducing beaver. Other species which may be reintroduced are wild horses, aurochs, elk, and reindeer.

While the American mustang population is declining rapidly, the wild horse population in Ladendorf aug 16 300x250Europe is increasing because horses there have proved they can be one of the keystone species for the regeneration of the land. They have been used to enhance the ecology at nature preserves in many places in Eurasia.

To find an optimal solution for our mustangs, my research suggests mustang advocates and those who administer the current management programs should investigate what conservation biologists have discovered and what has been accomplished and planned in other countries.

All photographs courtesy of Wikipedia.

Information Resources:

Forder, Victoria. Conservation Grazing: Konik Horse, European Beaver, and Wild Boar, Wildwood Trust, August 2006.

Fraser, Caroline. Rewilding the World: Dispatches from the Conservation Revolution. NY, Henry Holt, 2009.

Gill, Elaine. “An ecological mowing machine,” Ponies in the Wild, 1994, p. 117.

Janis, Christine. “The Evolutionary Strategy of the Equidae and the Origins of Rumen and Cecal Digestion,” Evolution, 30, Dec. 1976, pp. 757-774.

Ladendorf, Janice, “The Feral Horses of Sable Island,” Valley Equestrian News, May 17, 2016.

Laidlaw, Carol. “The Wicken Fen Vision: grazing an evolving landscape,” Conservation Land Management, Spring 2011, pp. 5-8.

Leste-Lasserre, Christa, “Exmoor Ponies Help Revamp the Czech Republic’s Landscape,” The Horse, Aug. 29, 2015.

Martin, Paul S. Twilight of the Mammoths. University of California Press, p. 110.

“New Milton pony grazing will ‘save money’,” BBC News, 9-16-14.

Simov, S.A. “Pleistocene Park; return of the ‘mammoths’ ecosystem,” Science, 2005, vol.  308, pp. 796-98.

“Upland Pony Grazing: A Review.” Dartmoor Commoners Council, 2016.

Vidal, John, “Wild herds may stampede across Britain under plan for huge reserves,” The Guardian, Oct. 27, 2005.