Beavers are changing the landscapes in the Arctic massively by building dams that melt permanently frozen ground and release greenhouse gases, according to a new study.
In recent years, beavers have spread to many tundra regions where they have never been seen before due to the lush vegetation.
But they are also building more dams in their new homes and creating a multitude of new lakes that thaw permafrost – permanently frozen soil – and release trapped gases such as carbon dioxide and methane into the atmosphere, which contributes to global warming.
German and American researchers spent 17 years studying satellite images of an area of approximately 38 square miles near the city of Kotzebue on the Baldwin Peninsula in Alaska.
They found that the number of beaver dams rose from just two in 2002 to 98 in 2019 – an increase of 5,000 percent, with more than five dams being built each year.
Higher temperatures lead to more bush land for beavers in the arctic tundra. Beavers therefore build dams in more areas, but the resulting waters are warmer than the surrounding permafrost, which remains completely frozen. The warmer lakes therefore accelerate the thawing of permafrost, which releases greenhouse gases such as carbon dioxide and methane.
A North American beaver (Castor canadensis) is working on its mother. This species is active in the arctic regions of Alaska
"Your methods are extremely effective," said Dr. Ingmar Nitze from the Alfred Wegener Institute for Polar and Marine Research (AWI) in Potsdam.
“Of course we knew that the beavers had spread considerably there in the past decades.
“But we never dreamed that they would take the opportunity so intensely.
"If you want to predict the future of permafrost, you should keep an eye on the beaver."
Mapping beaver dams in high resolution satellite imagery for the northern Baldwin Peninsula in Alaska. The position of individual dams is marked with a red arrow and the direction of flow with a light blue arrow
Location of the study area for mapping the beaver dam on the northern Baldwin Peninsula in northwestern Alaska
VIEW PERMAFROST AND GREENHOUSE GASES
Carbon is deep-frozen deep in Arctic permafrost – soil that remains completely frozen for at least two years – 0 ° C or colder.
As the earth warms up, scientists fear that some of the carbon in permafrost could escape into the atmosphere as carbon dioxide or methane.
An increase in the amount of these gases in the atmosphere could heat the Earth's climate even more.
More information: US National Snow & Ice Data Center
The furry rodents, which can weigh up to 30 kg, are armed with sharp teeth to cut down trees and bushes and to build dams.
These dams offer semi-aquatic beavers protection from predators such as wolves and bears by forming a large body of water.
Beavers build their lodges in the middle of these waters, which are made of sticks and mud like dams.
However, dams cause small valleys to fill with water and form new lakes that can easily measure a few hectares.
There are only two types of beaver – the Eurasian beaver and the slightly smaller North American, which is active in the Arctic regions of Alaska.
The Eurasian beaver originated in the UK and was widespread in England, Wales and Scotland, although British charities are now undertaking projects to reintroduce beavers.
In 2018, Dr. Nitze and colleagues found that North American beavers, which live in an 18,000 square kilometer section in northwest Alaska, created 56 new lakes in just five years.
This is partly due to climate change, as rising temperatures mean that more habitats provide the shrubs that animals need for food and building materials.
In summer, increased warmth and longer growing seasons have been associated with increased tundra productivity and shrub-dominated vegetation that attracted beavers over the past three decades.
However, the beavers' dams are warmer than the surrounding permafrost, which remains completely frozen (0 ° C or colder) for at least two years.
The warmer lakes therefore accelerate the thawing of permafrost, which releases greenhouse gases.
North American beaver (Castor canadensis) on the ground. Armed with sharp teeth, they felled trees and bushes and built dams, filling small valleys with water and forming new lakes that can easily measure a few hectares
The team used detailed satellite data to track North American beaver activity in two other regions of Alaska and to monitor where this cycle is occurring.
The lakes that used to be frozen are now more beaver-friendly thanks to the thinner layer of ice that covers the top in winter.
Beavers are also not hunted as intensely as in the past, which, according to AWI, means that it is a good time to be a beaver in the Arctic.
In addition to a 5,000 percent increase in the beaver dams on part of the peninsula, the larger area under investigation also experienced a beaver dam boom that affected the water balance.
"We see exponential growth there," said Dr. Nitze. "The number of these structures doubles approximately every four years."
Beavers deliberately work in parts of the landscape that are the easiest to flood.
To do this, they sometimes build up small streams or the outlets of existing lakes, which expand as a result, but prefer particularly drained lake basins.
"The animals intuitively found that the drainage channels at the sites of former lakes are being efficiently built up to create living space," said Benjamin Jones, University of Alaska Fairbanks lead investigator.
"This creates a new lake that breaks down the ice-rich permafrost in the basin and increases the depth of the technical water."
A Eurasian beaver (castor fiber). Castor includes two still existing species, the North American beaver (Castor canadensis) native to North America and the Eurasian beaver. Beavers are native to the UK and are common in England, Wales and Scotland
Over the course of the 17-year period examined, the total water area in the Kotzebue region grew by 8.3 percent – around two thirds of this was accounted for by beavers.
The research team claims that similar building booms have occurred in other regions of the Arctic, and they now want to extend their "beaver search" to the Arctic.
"Growth in Canada, for example, is most likely even more extreme," said Dr. Nitze
While the frozen ground could theoretically rebound after a few years when the beaver dams finally break, the conditions may not be cold enough to achieve this.
The study was published in Environmental Research Letters.
HOW AND WHY DO BEAVERS DAMS BUILD?
Beavers occur in the northern hemisphere and are among the most experienced builders in the world.
This reputation earned them the nickname "engineers of nature".
They felled trees by gnawing on their trunks and used the sticks to build dams to stop the movement of water in ponds, lakes, rivers and streams – and thus create waters with low currents.
The mammals then use sticks and mud to create a second structure – a large dome-shaped island that can reach a height of up to 3 m and a length of up to 500 m.
Each island has two underwater entrances and a living room above water where the animals sleep and seek shelter.
Beavers often line the walls of this chamber with dry leaves and plants to isolate them in winter.
It remains unclear why beavers build dams, but scientists speculate that the creatures use it in winter as warmth and protection and as protection from predators.
Beavers are strong swimmers, and the creation of a water reservoir enables animals to use their strengths to escape those who are higher in the food chain.
The largest beaver dam ever discovered was 850 m long – more than twice the length of the Hoover dam.
Forestry on the southern edge of Wood Buffalo National Park in northern Alberta, Canada was so extensive that it could be seen from space.
(tagsToTranslate) Dailymail (t) sciencetech (t) climate change and global warming