Letters: Save the horses at Theodore Roosevelt National Park
As a biologist, I have below summarized what I found out about positive impacts of horses on grasslands.
I have photographed and watched horses and other wildlife in Theodore Roosevelt National Park (TRNP) since 2014. I am seeing with concern that TRNP considers removing the herd of wild horses. One of the justifications is that horses have a negative impact on the grassland ecology. As a biologist, I have below summarized what I found out about positive impacts of horses on grasslands.
Horses have upper and lower incisors and can consequently clip the grass above the soil line. This leaves the plant alive and it can grow back. In contrast, cattle and bison are lacking the front teeth. Instead, they wrap their long and flexible tongues around the grass and can pull the entire plant out of the soil (at least when the grass is wet). The grass can then not grow back.
There are differences in the digestive system between horses and cattle/bison. Cattle and bison are ruminants with four stomachs, horses are considered semi-ruminants. Horses don’t degrade the vegetation, including seeds, completely. As a consequence, seeds pass through the system in a viable form. This helps the spread of plants, species diversification, and also aids the building of a nutrient rich soil. Cattle and bison degrade vegetation much more effectively. While this is an advantage for the animal and permits feeding on nutrient low vegetation, the feces does not contain viable seeds and is less nutrient rich.
An additional example of a positive impact of horses on grassland ecology, horses dig holes up to 6 feet to groundwater (in the deserts of North America). These are used by other species and decrease distance between water sources and increase germination of key riparian trees (riparian: situated by banks of river).
In summary of the above evidence, it is one sided to say that the impact of horses on grassland ecology is solely negative. Horses clearly have both negative and positive impacts. And this is where numbers matter. Overgrazing really is bad. I look forward to TRNP conducting the mandatory ecological study in a thorough way and letting us know how many horses the park can truly handle. My hypothesis is that it will be more than the 35 or 60 that were proposed in the best of the three options.