September 12, 2022

Beaver dam analogs bring ecosystem benefits in areas where habitat won’t support beavers

NM Game and Fish

A beaver dam analogue on the Rio San Antonio in Carson National Forest helps to facilitate restoring channel complexity and aid in grade control.

Beavers are increasingly viewed as an important part of the efforts to mitigate impacts of climate change, but in some parts of New Mexico the former beaver habitat has been destroyed.

In those situations, the New Mexico Department of Game and Fish will sometimes turn to man-made structures that mimic beaver dams. These structures are known as beaver dam analogs.

Ryan Darr, a spokesperson for the New Mexico Department of Game and Fish, said in an email that the department has seen the natural development of off-channel habitat as well as the expansion of riparian areas after the installation of beaver dam analogs. 

Within one or two growing seasons, the riparian and aquatic habitat improvements linked to beaver dam analogs have benefited wildlife and fish.

Darr said there are several types of beaver dam analogs. Some of them are classified as post-assisted. These require using untreated wood posts that are approximately three inches in diameter and mechanically driving them into the streambed. The posts are placed about 18 to 30 inches apart and then, Darr said, locally sourced materials like leaves, branches and live materials are woven between the posts. The holes are filled with turf, mud, sod, rocks and other local materials.

Darr said other beaver dam analogs are made without posts. These use stumps and root balls as well as piles of woody debris which are placed at strategic locations in a stream.

The beaver dam analogs help restore the habitat and may pave the way for beavers to eventually return to those stretches of stream.

Darr said beavers could possibly be reintroduced or they could expand upstream to the areas where the beaver dam analogs have helped to restore the habitat.

Beavers are often referred to as ecosystem engineers thanks to their impacts on streams, which include creating ponds and excavating canals and burrows along stream banks and in riparian areas.

Prior to European settlement in North America, scientists estimate that there were between 60 and 400 million beavers, which lived in all regions of the United States except for some of the arid southwest and the Florida peninsula. That number has been reduced to about 10 million.

“If you went back a little over 100 years, it would have been difficult to find beavers in most watersheds in the state because beaver populations and habitat were depleted due to the lack of regulations on industry, hunting, and trapping,” Darr said.

He said that one of the first game laws in the state was intended to restrict beaver hunting and trapping and, thanks to modern wildlife management practices, the beaver populations have been recovering.

“What we’ve found in recent years is that there are beavers in most of our watersheds across the state if there is suitable habitat, and in many places those populations are thriving,” he said. “Places where beavers may have been historically, but we don’t find them currently, usually don’t have suitable habitat and need improvements to riparian vegetation, aquatic habitat or land management practices to become suitable. These are locations where BDAs can often be applied successfully.”

Beavers were extensively hunted and trapped for their pelts. Beavers have also been considered pests that can cause flooding and property damage. 

In recent years, there’s been an increased push by states to promote beaver habitat recovery.

This week, California’s Department of Fish and Wildlife posted its first job opening for its new beaver restoration unit as the state looks to the semi-aquatic animal for help in the fight against climate change.

Beaver dams, and analog structures, can improve water quality by trapping sediment in the ponds created by their dams and by slowing water flows during spring snowmelt and monsoons, Darr said.

Even when the water is flowing at normal levels, the dams help some rivers and streams maintain consistent flows for longer during dry periods of the year, he said. This is because the dams slowly release the water.

The water in the beaver ponds tends to be colder during the summer months than flowing water in the river or stream, which benefits the fish species, Darr said.

While scientists have found numerous benefits to beavers’ activities, a recent review published this month in the journal Global Ecology and Conservation found that more work is needed. The review analyzed 267 peer-reviewed studies and found that most have been completed in temperate forest environments and that many biomes are understudied. The authors wrote that additional research is needed in some areas, such as in arid environments.

“Over the last decade, the introduction and conservation of beaver for stream restoration has become increasingly common. This study provides a reference for how specific variables may be expected to respond to beaver dams within and among biomes. It is important to note that each watershed is complex and has a unique combination of climate, underlying geology, soils, vegetation, biota, land use history, and current land use demands,” the authors wrote.