Beavers are known for the dams they create, but you may not know that these dams have a significant impact on the land and wildlife around them. So, how do beaver dams affect the environment? Do they create positive or negative impacts? And how would things change if beavers were to go extinct? In this article, we’ll answer all of these questions.
Why Do Beavers Build Dams?
You may think that beavers build dams for homes, and you would be partially correct. Beaver dams do play a large role in a beaver’s home environment, but not in the way you might expect.
Beavers don’t actually live in the dams they build; instead, they build them to create ponds of deeper water. 海狸实际上并不住在它们建造的水坝里;相反，他们建造它们是为了建造更深的池塘。Then, they build a lodge in the center of the water, where predators have a much harder time reaching them.
Beavers live in these lodges. The lodges have their foundation on the pond floor and extend several levels upward, eventually appearing above the water level.
Like beaver dams, the lodges are built of logs, rocks, and other natural materials. Beavers create underwater tunnels leading to and from their dams and lodges; these tunnels give them the best chance of escaping in cases of danger.
So, are the dams just there to hold the water in place? Do they have any other purposes?
Beavers typically create hollows and passages inside their dams, so they are able to come and go as they please. 海狸通常会在水坝内挖洞和通道，这样它们就可以随意进出。Sometimes they will use their dams to hide from predators such as bears, wolves, and river otters.
Sometimes, beavers will also use their dams as places of temporary shelter from sudden storms. During the summer and fall, they will hide stashes of food inside the dam, preparing for possible food shortages during the winter.
How Do Beavers Affect Their Environment?
Beavers are often considered a keystone species–they play a huge role in their local environments and ecosystems.
Beavers have many different effects on the environment, some positive and some negative. The important takeaway is that beavers have an important place not only in the animal kingdom but in the ecosystems they inhabit as well as the overall environment.
ARE BEAVER DAMS BAD FOR THE ENVIRONMENT?
In a large-scale, overall sense, beavers are not bad for the environment–in fact, they are highly beneficial. That said, in some areas, their dams may cause some regional problems.
In areas with a lot of beavers, the population may have to be managed to prevent the extinction of certain fish, unwanted structural changes to ponds and streams, and weakening of man made dams.
WHAT ARE THE NEGATIVE EFFECTS OF BEAVER DAMS?
Some local problem that may be caused specifically by beaver dams are as follows:
Beaver dams can interfere with fish migrations: In some places, certain species of fish migrate between large lakes and breeding grounds. If beavers build dams along the migratory routes, these fish may not be able to get through, which in turn can affect their reproduction and reduce their numbers.
Beaver dams may cause flooding: The primary reason beavers build dams is to dam up streams and rivers to create areas of standing water. Obviously, there are areas where this could cause flooding problems.
Even if it hasn’t rained recently and the water levels are fairly low, having a beaver dam redirect water into low-lying areas can cause structural damage as well as changes to the local ecosystem. The damage may be even worse during rainy periods.
Beaver dams may affect water temperature: According to KingCounty.Gov, average water temperatures are nearly 5 degrees Fahrenheit cooler downstream from a beaver dam. While this can sometimes be viewed in a positive light, it can also impact what types of fish and other wildlife are able to live downstream of beaver dams.
BENEFITS OF BEAVER DAMS
Of course, as noted above, beavers also produce many beneficial effects on the environment. These effects include:
Beaver dams create new wetland areas: By creating new pools of water, beaver dams can attract a variety of new flora and fauna into the area. These ponds can also prevent flooding by collecting large amounts of water and slowing down what is lost in runoff.
Beaver dams allow for woodland diversity: because of all the species of animals that thrive around wetlands, beaver dams promote biodiversity in the local ecosystem.
Beaver dams filter the water: As water drains through the filter-like weave of the dam, much of the sediment and debris is strained out. This leads to a source of purer, cleaner water downstream from the dam.
Beaver dams help protect the land in the face of climate change: Beaver dams help to reduce erosion by storing more water and reducing runoff. The ponds they create also store carbon, keeping it from being released in large quantities into the air.
What Would Happen If Beavers Went Extinct?
Since beavers have such an impact on the ecosystems they inhabit, the world would be a much different place without them.
Some areas would become choked with too many trees, as there would no longer be the beavers to thin out the trees and create space for new trees. The most aggressive plants would dominate the area, which would become overgrown within a matter of seasons.
This would lead to less diversity of species. Some species that depend on beavers and their dams, such as many kinds of birds, would probably suffer endangerment or have to find ways to adapt to a different environment.
Conclusion
Beavers have many important roles to play in wildlife (and they can even find a way to your yard). The dams they create can change the face of the land by causing the water from streams and rivers to pool, leading to the formation of ponds and wetlands.
Because many different species of animals rely on beaver dams and the wetland areas they create, beavers can lead to the formation of a more diverse ecosystem. They can even reduce erosion from water runoff and store carbon in the ponds they create.
As climate change worsens water quality and threatens ecosystems, the famous dams of beavers may help lessen the damage.
That is the conclusion of a new study by Stanford University scientists and colleagues, publishing Nov. 8 in Nature Communications. The research reveals that when it comes to water quality in mountain watersheds, beaver dams can have a far greater influence than climate-driven, seasonal extremes in precipitation. The wooden barriers raise water levels upstream, diverting water into surrounding soils and secondary waterways, collectively called a riparian zone. These zones act like filters, straining out excess nutrients and contaminants before water re-enters the main channel downstream.
This beneficial influence of the big, bucktoothed, amphibious rodents looks set to grow in the years ahead. Although hotter, arid conditions wrought by climate change will lessen water quality, these same conditions have also contributed to a resurgence of the American beaver in the western United States, and consequently an explosion of dam building.
“As we’re getting drier and warmer in the mountain watersheds in the American West, that should lead to water quality degradation,” said the study’s senior author Scott Fendorf, a professor of Earth system science at Stanford University. “Yet unbeknownst to us prior to this study, the outsized influence of beaver activity on water quality is a positive counter to climate change.”
A lucky natural experiment
The discovery of the profound impact of beaver dams came about serendipitously. As a PhD student in Fendorf’s lab in 2017, lead study author Christian Dewey had started doing field work along the East River, a main tributary of the Colorado River near Crested Butte in central Colorado.
Initially, Dewey had set out to track seasonal changes in hydrology, and riparian zone impacts on nutrients and contaminants in a mountainous watershed.
“Completely by luck, a beaver decided to build a dam at our study site,” said Dewey, who is now a postdoctoral scholar at Oregon State University (whose mascot, incidentally, is a beaver). “The construction of this beaver dam afforded us the opportunity to run a great natural experiment.”
Dams versus dry years and wet years
For the study, Dewey and colleagues reviewed data on water levels gathered hourly by sensors installed in the river and throughout the riparian area. The team also collected water samples, including from below the ground’s surface, to monitor nutrient and contaminant levels.
To understand how beaver dams may affect water quality in a future where global warming produces more frequent droughts and extreme swings in rainfall, the researchers compared water quality along a stretch of the East River during a historically dry year, 2018, to water quality the following year, when water levels were unusually high. They also compared these yearlong datasets to water quality during the nearly three-month period, starting in late July 2018, when the beaver dam blocked the river.
Water quality is a measure of the suitability of water for a particular purpose – ecosystem health or human consumption, for instance. During periods of drought, as less water flows through rivers and streams, the concentrations of contaminants and excess nutrients, such as nitrogen, rise. Major downpours and seasonal snowmelt are then needed to flush out contaminants and restore water quality.
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Through their measurements and computer modeling of the interlinked biological, chemical, and physical processes that affect how contaminants become concentrated or flow downstream, the researchers found that the beaver dam dramatically increased removal of nitrate, a form of nitrogen, by creating a surprisingly steep drop between the water levels above and below the dam.
Warm, dry summers following spring snowmelt also produce big level changes, which generate a pressure gradient that pushes water into surrounding soils. The larger the gradient, the greater the flow of water and nitrate into soils, where microbes transform nitrate into an innocuous gas.
In the East River, the researchers found the increase in the gradient compared to an average day was at least 10 times greater with the dam than it was during the summer peak without the dam, for both the high-water year (2019) and the drought year (2018). Stated otherwise, the effects of the dam exceeded climatic hydrological extremes – in either direction of drought or abundant snowmelt – by an order of magnitude.
“Beavers are countering water quality degradation and improving water quality by producing simulated hydrological extremes that dwarf what the climate is doing,” said Fendorf, who is the Terry Huffington Professor in the Stanford Doerr School of Sustainability and a senior fellow at the Stanford Woods Institute for the Environment.
While in place, the beaver dam boosted removal of unwanted nitrogen from the studied East River section by 44% over the seasonal extremes. Nitrogen is an especially pernicious problem for water quality as it promotes overgrowth of algae, which when decomposed starve water of the oxygen needed to support diverse animal life and a healthy ecosystem. 氮对水质是一个特别有害的问题，因为它会促进藻类的过度生长，当藻类分解时，会使水中缺乏支持各种动物生命和健康生态系统所需的氧气。
The study is a reminder that as the future impacts of climate change are holistically assessed, feedback from changes in ecosystems must also be included.
“We would expect climate change to induce hydrological extremes and degradation of water quality during drought periods,” said Fendorf, “and in this study, we’re seeing that would have indeed been true if it weren’t for this other ecological change taking place, which is the beavers, their proliferating dams, and their growing populations.”
