Scientists and biologists also believe the horses damage the ecology of the Salt River area, but the National Forest Service has not performed a formal study on the environmental impact the horses have.

”That question has been asked many times – as far as what damage they do, and we haven’t answered the question, because we do not have any scientific data one way or the other,” Templin said.

The National Forest Service has conducted a carrying capacity test, which evaluates how many of any given animal an area can support, but its results are not yet completed. The test is expected to determine how many structures, feeding troughs and fences will be needed to support the horse population.

Although cattle had been allowed to graze in the Salt River area for decades, by the 1980s, the environmental impact of cattle was understood and the Tonto National Forest Service stopped granting grazing permits.

In doing so, Tonto National Forest Service intended to allow the area to recuperate. This area, though, is now subject to grazing from the horses, which can be much more damaging.

Mark Lawerson, president of the Maricopa Audubon Society, said the horses cause worse environmental damage than the cattle that are banned from grazing.

“Cattle use their tongues to rip off grass and eat it. Horses use their teeth, down really low, practically to the root, and chomp it off or pull it out. So, horses are more environmentally damaging than cattle,” he said.

Horses and cattle did not evolve in the Sonoran Desert, and the effects that such large animals can have on the landscape goes beyond the overgrazing of plants.

“They are heavy, so their hooves damage a lot,” Lawerson said. “The natural world out there is not built to accommodate big herbivores like that.”

For instance, the combination of a horse’s weight and its hooves ruins the biotic crust of the soil, leading to poor absorption of water, Lawerson said. The horses also loosen the dirt, which can then be kicked up by wind and carried into the river.

The constant weight of horse hooves has turned areas that were once lush with cottonwoods and grass into brown, vacant expanses of loose dirt, Lawerson said. Entire bosques of mesquite trees look completely different than they did five years ago.

Horses also roam for longer and further than cattle, so they damage a larger area.

Lawerson said he’s seen the area change first-hand, and for the worse.

“Just two or three years ago, I was in this exact spot,” Lawerson said, standing in the Butcher Jones recreation area, describing the grass, herbs, annual plants and weeds that naturally grew below the canopy of desert trees in the riparian areas surrounding the Salt River.

Now, the area is barren and dusty. Horse hoof prints are visible in the loosened and trampled dirt. Lawerson pointed out the few scattered plants, some with signs of horse grazing. Those conditions, he explained, leave the area more prone to erosion, as the soil is easily kicked up by wind, people or animals.

That topsoil also ends up in the river, creating excess sediment, where it damages fish habitats and clouds the water. That, in turn, obscures the fish for birds – including the golden eagles native to the region – that prey on them.

The Salt River horses compete with the native birds in other ways, Lawerson said. The horses’ grazing on the natural vegetation means birds are left with less food, and less building materials for their nests.

“Those plants produce seeds, and a lot of seed-eating birds like to eat them, and we have a lot of birds here in the winter that do eat seeds, like sparrows,” he said “They existed on weed seeds and grass seeds like this, obviously, once upon a time.”

Netherlands, of the Salt River Wild Horse Management Group, said she disagrees with the scientists and National Forest Service evaluation of the horses’ negative environmental effects, because she thinks the nutrient-rich manure could have some positive effect on vegetation.

Much is still up in the air concerning the Salt River Horses. The National Forest Service and Arizona Department of Agriculture are still assembling their working group of citizens to determine what needs the management plan needs to address. Meanwhile, as the wheels of bureaucracy turn, the Salt River Horses continue to damage the ecosystem around them.

“They are not native to this desert the Sonoran Desert,” Lawerson said. “They should be well taken care of, where there is veterinary care and where there are people who can take care of them and do the right thing and manage them. Right now, this population of probably 500 horses in the Salt and Verde rivers is unmanaged, uncared for and damaging the natural world.”