Plans are underway to declare habitat loss from New South Wales brumbies a key threatening process, with their hooves and grazing habits blamed for the destruction of environments where they roam.

Brumbies are synonymous with Australian folklore, linked to the legendary Man From Snowy River.

They not only roam the Snowy Mountains, but also the NSW north coast, Northern Tablelands, the Hunter Valley, Blue Mountains and far south coast.

Scientists believe there are at least 10,000 feral horses in the state.

"They now occupy over 3,000 km2 of the Australian Alps National Parks in New South Wales and Victoria and their range is expanding," the NSW Scientific Committee said.

The committee, part of the Office of Environment and Heritage, has now moved to make a preliminary determination to list habitat loss from brumbies as a key threatening process.

"Feral horses have a range of flexible physiological, behavioural and morphological attributes that have enabled them to thrive under a wide range of ecological conditions," it said.

Park officials previously drafted a management plan to limit the number of brumbies in Kosciuszko National Park. ( ABC TV )

Brumbies blamed for altering vegetation

The committee said the damage caused by wild horses was extensive.

"They actually do change the structure of the soil and the vegetation quite a lot, so these communities are getting damaged and threatened species found in these communities are finding it harder to survive," it said.

The destruction involves habitat damage in streams, wetlands and adjacent riparian systems.

Committee chairman Marco Duretto said another problem occurred through selective grazing, trampling, track creation and soil compaction.

"Unfortunately wild horses are threatening some existing threatened communities, especially up in the high country, things like the alpine sphagnum bog," he said.

The damage is not limited to the Snowy Mountains, with Oxley Wild Rivers National Park having up to 1,000 horses.

The committee said the Blue Mountains National Park had up to 70 horses, the Guy Fawkes National Park more than 1,000, and the Barrington Tops National Park about 100 horses.

Fears about potential mass cull

Hunter Valley Brumby Association vice president Maddison Young, who is also an environmental scientist, feared the threatening process listing could pave the way for a mass brumby cull across NSW.

"We know they're keen to start something like a ground shoot," she said.

"At the moment aerial culling is off the table, but that is only because of pressure from the public.

"If they were able to change that perception they would definitely like to use it."

Ecologists and National Parks and Wildlife officers have previously proposed a 90 per cent cull to protect rare vegetation and wetlands that many feared could be destroyed forever.

Space to play or pause, M to mute, left and right arrows to seek, up and down arrows for volume. Watch Duration: 7 minutes 10 seconds 7 m The wrangling over what to do with the wild horses of the Snowy Mountains

Climate change expected to worsen Snowy brumby threat

The committee said climate change had increased the risk posed by brumbies, particularly in the fragile alpine environment.

"Climate change is leading to the uphill movement of the snowline," the committee said.

"Changes to snow permanence, snow area and depth along with altered precipitation regimes are projected to continue under future climate scenarios.

"These climate change impacts are likely to increase the area of habitat available to feral horses in winter, increasing the carrying capacity for horses."

The committee said the habitat loss caused by brumbies warranted a threatening process listing for a number of reasons.

"Habitat degradation and loss by feral horses is eligible to be listed as it adversely affects threatened species or ecological communities," it said.

It added the habitat loss could also cause species or ecological communities that were not threatened to become threatened.

That is the case in a national park north of Newcastle.

"Feral horse impacts have also been reported to have increased in the last 10 years in the Barrington Tops region, which is within the habitat of the broad-toothed rat," the committee said.

The proposal to list habitat degradation and loss by feral horses as a key threatening process is on public exhibition until June 22.