Sunday, November 7, 2010

Annotation: Management Implications of the Ecology of Free-Roaming Horses in Semi-Arid Ecosystems of the Western United States

Beever, Erik A. (2003). Management Implications of the Ecology of Free-Roaming Horses in Semi-Arid Ecosystems of the Western United States. Wildlife Society Bulletin 31(2). 887-895.

In this commentary, Erik Beever, draws from his research in 9 Herd Management Areas (HMA) to highlight the influence free-roaming horses have on the landscapes of the Great Basin. He has studied many aspects of feral horse disturbances, from percent cover of plant species to small mammals.

Due to the history of feral horses, and the policies surrounding their management, they have have a unique influence on rangelands. Horses evolved in North America, but disappeared between 10,000 and 14,000 years ago. The current theory for their disappearance, along with many other taxa that also went extinct, is that the climate changed, which resulted in vegetation shifts, and they were also hunted by various predators, including humans. In the 16th century, domestic horses were brought to the southwestern United States by the Spaniards. From this initial introduction, and the relationship humans had with horses, their population peaked at 2-7 million in the 19th century. Then the Taylor Grazing Act 1934 initiated persecution, capture, and removal of horses. 

Following this, their populations declined through the late 19th century and through to the mid-20th century. Their populations again began to rise after the Wild Horse and Burro Act was passed in 1971. This act began the study of the ecology of free-roaming horses.

Feral horses are more socially dominant than cattle when interacting with native wildlife. This effects native wildlife use of the area. Studies of horse and ungulate interactions have been conducted, and are improving greatly. However, interactions that horses have with non-ungulates is only beginning and such studies will be important in understanding how horses affect various components of their environment.

Horses have a unique influence on the landscape, this is important to understand for management purposes. Many compare their influences to cattle use of the rangelands, but horses are unique. They are cecal digesters, which means that they are not selective in their forage. A low-quality diet means that horses will consume 20-65% more forage than a cow of an equivalent body mass. Horses also use the landscape heterogeneously, leaving many trails that are used repeatedly and go long distances. Cows, on the other hand, use the landscape in a more uniform manner. Their trails are not as used, nor as long – as Beever observed. As a result of this, horse occupied sites have greater soil penetration resistance. Further differences between horses and cows are as follows: horses have a flexible lips and upper front incisors when compared to cattle. Such differences mean that horses can graze vegetation much more closely to the ground than cattle.  This will delay the recovery of vegetation.

Now that we know their unique influence on the landscape, they also have unique management plan when compared to cattle, and native ungulates. Horses are not as intensively managed as cattle. Cattle are managed on public ranges with fencing exclosures, rotation grazing, herding, and they are supplied with water. Horses are not fenced, and are managed with minimal strategies. Unlike with native ungulates, hunting of horses is not permitted, as they have federal protection under the Wild Horse and Burro Act, 1971.

In conclusion, Beever's purpose was to highlight the differences of horse influences when compared to cattle and native ungulates. He argues there needs to be careful monitoring for ecosystems that have had little, or infrequent, grazing over evolutionary time in order to avoid deterioration.

This was a great commentary of what Beever has researched and studied in the past. Compared to another article he wrote on characterizing the grazing disturbances of horses, he went into more detail here about soil penetration. In his former article, he never outright discussed or addressed the increased soil penetration in horse occupied sites compared to horse removed sites. As a result, I found this article to be great for my research as it explained the unique influences horses have on the landscape when compared to other ungulates, and also the unique way they are managed.

Beever was trying to reach managers, biologists, and the general public, who perceive the ecology of free-roaming horses to be comparable to cattle. His article addresses the differences that these two ungulates in fact have on the landscape, and that horses have a unique influence. This is important to understand for management purposes in deciding appropriate management levels of horse herds.

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