This area of ​​the United States has been extensively destroyed, and the culprit is actually the local "infrastructure maniac"?

From the perspective of biodiversity, the Arctic tundra is not as lonely and desolate as a desert, but it is far less lively than a tropical rainforest. The thick permafrost below makes it difficult for tall plants to take root and grow, so it has become a world of mosses, lichens, some herbs and short shrubs. Some animals will visit from time to time, such as Arctic hares and moose. For them, the food on the tundra is not delicious, but it is enough to fill their stomachs. Precipitation and melting snow have caused water to flow on the tundra. If you are lucky, you can also see salmon in the water. When it is slightly warmer, some migratory birds from the south will come here to stop. Although the cold of the Arctic cannot keep their winter, it at least leaves them with memories of their summer.

A spot in the Arctic tundra of Seward Peninsula, Alaska, USA. The top picture is an infrared aerial photo from 1980, with blue arrows indicating the direction of water flow; the bottom picture is a satellite photo from 2019, with white arrows pointing out some more obvious dams. Image source: Tape.et al, 2022

The Arctic tundra is like a quiet town, deserted but not lonely. At this time, someone built a "water conservancy project" on the tundra.

The two photos below are infrared aerial photos from 1980 and satellite photos from 2019, showing the same Arctic tundra stream on the Seward Peninsula in Alaska, U.S. From the sky, the stream in 1980 was just a thin line, but by 2019, this thin line had "expanded" into multiple ponds.

The appearance of these ponds was not caused by mountain torrents or wildfires, nor by earthquakes or land subsidence, but by "people" building a large number of dams on the streams, blocking the flow of water, which then spread to the surrounding areas and gradually accumulated into ponds.

Dams appearing on the Arctic tundra. Image adapted from: Tape et al, 2018

Although such projects look like human work, the fact is that they are not. The construction of water conservancy projects in these places is not allowed by local laws. Of course, these laws can only govern humans, not the famous "infrastructure demons" in nature who are good at building dams - beavers . These dams are their masterpieces, and they have obviously expanded their "infrastructure business" to the Arctic tundra.

Beaver: You never imagined that I built all the dams.

01

Hydraulic Engineer

There are two species of beavers in the world. The one "decorating" the Arctic this time is the North American beaver (Castor canadensis), which mainly lives in North America; the other beaver is called the Eurasian beaver (Castor fiber), which is also distributed in my country.

The webbed paws and paddle-like tails of beavers make them good swimmers in water, but once on land, they become inconvenient fur balls and are easily eaten by natural enemies such as wolves and coyotes. Therefore, in order to stay in the water as much as possible, where they feel more secure, beavers have engraved the skills of "hydraulic engineers" into their genes.

Beavers' webbed feet and paddle-like tails make them good swimmers, but they have trouble moving on land.

The construction of the dam stems from the beavers' pursuit of a "lake villa". Beavers' dens are usually located in "log cabins" built on the water with branches and mud. The entrance of the "log cabin" is underwater, and there is a small hole on the top for air circulation in the den. Beavers enter and exit the den through the underwater entrance, so their whereabouts are more hidden from predators.

Schematic diagram of beaver nest, drawing: Ma Dongyuan, original picture source: Pixabay, photography: Bridesmill

However, they are not satisfied with just such a "log cabin". The surrounding environment must also be comfortable enough! The water flow around the nest cannot be too fast, and it is best to have still water, otherwise the "log cabin" will be unstable; the water level must be high enough to ensure that the entrance can be built underwater; the surrounding water area must also be wide enough so that they have more space to move around, and they can walk less on land when looking for food, and swim away in time when encountering danger; the water temperature must also be appropriate, not too cold.

So the beavers began to build dams. They first blocked the water flow with silt, branches, small stones, etc., and then used tree trunks to continuously reinforce and repair it, and finally built one dam after another. Under the action of the dam, the river bank zone expanded, the water level rose, the water volume was large, and the water flow was slow, which could better preserve heat and make it warmer . After the dam was built, they would come back from time to time to check, repair, and reinforce it to ensure the normal operation of the dam. Not only that, the beavers would also build many small "canals" around to expand their waterways, sometimes to facilitate the transportation of wood for dam construction, and sometimes to be closer to food. In short, wherever the beavers go, various "water conservancy projects" are almost indispensable.

A dam built by beavers. Copyright image, no permission to reproduce

02

The dam is being repaired

The North Pole

“The scale and speed at which beavers are transforming the Arctic landscape looks like a fire burning in the Arctic when viewed from the air,” Ken Tape, an ecologist at the University of Alaska Fairbanks, said in an interview.

In the past, beavers were not considered to be animals that could survive in the Arctic, and the Arctic tundra did not seem to be a suitable habitat for beavers: most of the area was covered with ice, so the "hydraulic engineers" could not use their dam technology or find a place to build their "log cabins." The thin layer of vegetation on the tundra also made it impossible for them to find "building materials" for dams, and there was very little food.

But the past is different. Today, under the trend of global warming, the Arctic region is also facing the problem of climate change. Since the end of the 19th century, the average temperature in the Arctic region has risen by 1.8℃. As the temperature continues to rise, the time for flowing water to freeze is shortened, the growing period of plants is extended, and more shrubs (and even trees) have grown. The environment is gradually changing, and those guests who were reluctant to come in the past are now happy to visit, and beavers are one of them.

In the Arctic tundra, beavers build dams around their nests, transforming the surrounding environment into "beaver ponds." Image source: Tape. et al, 2018

Through the study of remote sensing data from the Arctic tundra in Alaska over a period of 70 years (1949-2019) and interviews with local residents, Tap and his colleagues found that beavers first came here to build dams and form "beaver ponds" around 1980, and the number of dams continued to increase. In the decade from 2003 to 2017 alone, the number of "beaver ponds" in most areas doubled . As of 2019, they have discovered a total of 11,377 "beaver ponds".

Density map of 11,377 beaver ponds in the Arctic tundra of Alaska, USA. Image source: Tape et al. 2022

"There aren't many animals that leave traces on Earth that can be seen from space, like beavers do. Of course, the only other animal that has this ability is humans," said Tap.

Beavers' "water conservancy projects" undoubtedly make them keystone species that significantly affect the ecosystem and species composition in the forests south of the Arctic tundra. Beaver dams change the flow rate, water level, temperature and other properties of water, thus changing the composition of invertebrates and microorganisms in the water, thereby changing the nutrient composition of the water. For fish, dams may hinder the migration of fish on the one hand, but on the other hand, they provide a suitable spawning and reproduction environment for many fish. Factors such as river bank widening provide growth conditions for many riparian plants, and then there are animals that feed on these plants or birds that live on them... Studies have shown that beavers also play a key role in soil and water conservation and drought prevention in their wetland ecosystems. Once, American scientists even successfully used "beaver dams" to save a species of rainbow trout (Oncorhynchus mykiss) by introducing beavers into rivers.

The ecological role of beavers cannot be underestimated. American scientists have successfully used "beaver dams" to increase the number, survival rate and reproduction rate of rainbow trout. Image source: Oregon State University

03

Blessing or curse?

The arrival of beavers in the Arctic may be a good thing for the biodiversity of the Arctic itself, but it may not be a good thing for the global climate.

There is no definitive conclusion yet on what the arrival of beavers means for the Arctic ecosystem, but Tap and his colleagues have made very positive predictions. The frozen water environment and low temperatures have kept many organisms away from the Arctic tundra. The emergence of "beaver ponds" has increased the surface water area and depth, making it more able to retain heat and less likely to freeze, and is likely to attract many new aquatic species to migrate here.

"Want to play with me?" Copyrighted image, unauthorized reproduction

Although there are several species of salmon in the Arctic tundra, they used to just pass by. The changes in the water environment caused by beavers have provided these salmon with the possibility to spawn and reproduce here. Minerals stored in the frozen soil may also be exposed with the beavers' "water conservancy projects", promoting the growth of surrounding shrubs, and the rise of shrubs will attract more other creatures. The appearance of beavers may be like building some markets in this quiet town in the Arctic tundra, gradually attracting scattered residents around to come and party, and slowly turning it into a lively place.

Beavers may have a positive impact on the biodiversity of the Arctic tundra, but one of their possible negative effects deserves our attention. The price of the thriving vitality of "beaver ponds" is the melting permafrost. According to estimates, the carbon content in permafrost is about twice that in the atmosphere. The sudden thawing of the permafrost will release the carbon dioxide and methane in it, continuing to exacerbate climate change. The areas flooded by "beaver ponds" will cause the permafrost underneath to thaw. If beavers continue to build dams on a large scale in the Arctic tundra, they may really be "burning the Arctic" and continuing to release greenhouse gases from the permafrost.

Changes to the water environment of the Arctic tundra caused by beavers. Red arrows indicate beaver dams and yellow arrows indicate possible locations of permafrost melting. Image source: Jones et al, 2020

Beavers came to the Arctic because of climate warming, and they may continue to exacerbate global warming. Tape and his colleagues also predict that the number of beavers in the Arctic tundra will increase in the future, and their range of activities will move further north. More research and management of Arctic tundra beavers in the future will also be important.

But whether it is good or bad, one thing is certain: the future of the Arctic tundra in Alaska, USA, is undergoing dramatic changes due to the arrival of beavers.

Potential impacts of beavers on the Arctic tundra. Image source: Tape et al, 2018

References:

[1] https://www.nature.com/articles/s41598-022-09330-6

[2] https://onlinelibrary.wiley.com/doi/full/10.1111/gcb.14332

[3] https://iopscience.iop.org/article/10.1088/1748-9326/ab80f1?utm_source=mp-fotoscapes#erlab80f1f8

[4]https://web.archive.org/web/20200123132507/https://www.aphis.usda.gov/wildlife_damage/beaver_damage/downloads/Baker%20and%20Hill%20Beaver%20Chapter.pdf

[5] https://wires.onlinelibrary.wiley.com/doi/10.1002/wat2.1592

[6] https://www.nature.com/articles/srep28581

[7] https://www.businessinsider.com/beavers-invade-alaska-arctic-tundra-photos-satellite-images-damage-2023-1

[8] https://www.livescience.com/why-beavers-build-dams

[9] https://animaldiversity.org/accounts/Castor_canadensis/

[10] https://ucmp.berkeley.edu/exhibits/biomes/tundra.php

This article is a work supported by Science Popularization China Starry Sky Project

Team Name: Global Science

Author: Ma Dongyuan

Produced by: China Association for Science and Technology Department of Science Popularization

Producer: China Science and Technology Press Co., Ltd., Beijing Zhongke Xinghe Culture Media Co., Ltd.

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