There was a lot of controversy when beavers (Castor fiber) were introduced to Devon in the southeastern part of England in 2011, as part of a study designed to determine if England should reintroduce beavers into their ecosystem all over the country. Many farmers and landowners opposed the experiment, claiming that the beavers would damage their farms or property by flooding or degrading the habitat.

The beavers used to be all over England, but went extinct after being hunted for the pelts in the 16th century. The pelts were very warm, and therefore fetched a high price. Sadly the beaver is easy to hunt, to once hunters started shooting them, the numbers fell down extremely quickly. During this period they almost went extinct all over the world, but luckily a few populations survived, and has since been used as reestablishment animals in other countries.

An Eurasian beaver (Castor fiber). Image by Martina Lion, posted with the Creative Commons Attribution-Share Alike 3.0 Unported license.

Six years after the release in Devon, the preliminary findings from the study became released to the public, and just like what most ecologists would expect, the beavers turned out to be very good for the environment. Beavers are a keystone species in the ecosystem they live in, and are even able to transform one habitat into another by changing how the water flows in the river. For this reason they are known as ecosystem engineers, and many species thrive in the presence of beavers that create a suitable habitat for them to live and feed in.

The results so far show that the water that flows downstream from the beaver habitat is up to three times cleaner than the water upstream from the beaver pond, which is obviously a good thing for humans. In addition, the pools they create by damming the river are able to store 17.6 tons of carbon and 1.1 ton of nitrogen. This is very needed is areas close to where agriculture with fertilizers are taking place, because this often tend to release excess nitrogen into the river system.

How reintroduced beavers affect the ecosystem

Once beavers are introduced or reintroduced into an area, they will first create a hut. Once that is complete, they will start to create dams in the river or stream to stop the water from flowing too fast. This will usually lead to a rise in water levels in the surrounding areas, often flooding plains in several hundred meters around the dam.

Once the dam is completed and the area around it is flooded, the entire ecosystem will in time change. The newly flooded area will be very rich in nutrients, and be very attractive for insects. Once they insects start getting high numbers, birds and fish will also be more abundant. This again attracts more predators, and at this point the small river area has become a thriving ecosystem that supports many different animal species on different trophic levels.

In Devon, the researchers noted that the amount of clumps of frogspawn had increased from only 11 clumps in 2011 to 681 in 2017! This is due to the newly flooded plains being so rich in insects, which is the primary food being eaten by frogs.

A beaver dam in Sweden. As you can see, a lot of water is stored there. Image by Lars Falkdalen Lindahl, posted with the Creative Commons Attribution-Share Alike 3.0 Unported license.

The beavers had effects on the environment as well as the biota, and the beavers themselves prevent the area from experiencing a high level of soil erosion. This can be a huge benefit to the area, especially if it is close to agriculture, which often have problems dealing with too rapid soil erosion on the land. Their dams also provide the area with flood preventing, because the pools above the dams are capable of storing large amounts of water. This if useful when it is extremely heavy rain, and several dams along a river can certainly prevent flooding disasters downstream. However, there is also flood risk associated with the beaver dams, because if they were to collapse because of the heavy rainfall, a huge amount of water could potentially be released downstream at once, which could have devastating effects!

All in all, the beavers provide several good ecosystem services, and I’m sure they will be regarded with high gratitude in England once they have gotten used to the idea. At this point the scientists are still looking at the data from Devon before determining if they should reintroduce beavers into other areas of England, so it will be exciting to see if we can finally see wild beavers all over England in the future!

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