How beavers are reviving wetlands

A happy beaver

A happy beaver

We are losing wetlands three times faster than forests, according to the Ramsar Convention on Wetlands. When it comes to restoring them to their natural state there is one hero with considerable powers – the beaver.

Wetlands store water, act as a carbon sink, and are a food source. The Ramsar Convention on Wetlands says they do more for humanity than all other terrestrial ecosystems – and yet they are disappearing at an alarming rate.

The main problems are agricultural and urban expansion, as well as droughts and higher temperatures due to climate change.

But if you have a river and a beaver it might be possible to stop this process.

These sharp-toothed rodents build dams on waterways to create a pond, inside which they build a “lodge” where they can protect themselves from predators.

Their technique is to chew tree trunks until they fall, and use the trunk and branches as building materials, along with stones at the bottom, and mud and plants to seal the upstream wall of the dam .

The dam creates floods, slows the flow of water and keeps it on the landscape for longer.

“This turns simple streams into thriving wetland ecosystems,” says Emily Fairfax, an ecohydrologist at California State University.

“Because of the amount of food and water available in their wetlands, they are a great habitat for many different species. That’s part of the reason why beavers are called flagship species.”

A tree chewed by a beaver

Beavers chew the base of selected trees until they fall

Over the past 50 years, Canada and several states across the US have reintroduced beavers. Initially this was done to bring back the number of bears, after they were almost extinct for their fur and meat in the 19th Century.

But wetland ecosystem restoration has major biodiversity benefits, including the return of many species of frogs, fish and invertebrates.

A 2018 study by Finnish researchers found that beaver-engineered ponds contained almost twice as many mammal species as other ponds. Easels, otters and even moose were more common.

“Beaver wetlands are quite unique,” says Nigel Willby, professor of freshwater science at the University of Stirling.

“Anyone can make a pond, but beaver ponds make really good biodiversity, partly because they’re shallow, littered with dead wood and generally messed up by beavers feeding on plants, digging canals, repairing dams, building lodges etc.

“Essentially, beavers prefer to create complex wetland habitats that we would never be able to match.”

Beavers keen

  • Dams built by beavers can be up to 5m high, and the largest recorded so far – in Alberta, Canada – is 850m long

  • When beavers cut down trees, tree stumps often grow new shoots instead of dying – effectively the beavers defoliate

  • The North American beaver and the Eurasian beaver were confirmed as separate species in the 1970s

A healthy wetland ecosystem also sequesters a large amount of carbon, and by acting as a sponge and soaking up floodwaters it can mitigate the effects of climate change, scientists say.

Wetlands store water during wet seasons and release it slowly during dry periods.

“When you go into a period of drought, all the plants that live in a floodplain depend on water stored in the soil to stay green and stay healthy. If they don’t get enough water they will start to wilt and die and drying.,” says Dr. Fairfax.

Beaver dam at sunset in Grand Teton national park in Wyoming, USA

A beaver dam in Wyoming, USA

She and her team studied 10 different wildfires in five US states between 2000 and 2021 and found in all of them beavers and their ecosystem engineering reliably created wetland habitat, even during megafire events.

“Beaver wetlands have a lot of stored water, so plants in them don’t really feel droughts, they stay green and lush. And when a wildfire came through, they didn’t burn and we found that they stayed submerged well.”

But experts say beavers are only part of the solution to restoring wetlands. Among other measures that are necessary are the planting of woodland on the banks of lakes and rivers, and the restoration of bogs and salt marshes, says Professor Willby.

And most importantly, beavers are only found naturally in North America and Eurasia.

Bringing them into inappropriate places can be counter-productive. This was demonstrated in Argentina and Chile, where beavers introduced from North America in the 1940s increased exponentially in the absence of predators, leading to massive forest loss.

The Global Wetlands Outlook published in 2021 by the Ramsar Convention on Wetlands found that the most extensive decline in wetlands was in Africa and Latin America and the Caribbean.

Lake Chad

Lake Chad is a shadow of its former self

The significant shrinkage of Lake Chad, closer to the border with Chad, Cameroon and Nigeria in West Africa is one of the most striking examples.

It has decreased by 90% since the 1960s mainly due to a sharp increase in water demand from a rapidly growing population, unplanned irrigation and now drought due to climate change.

“There have already been conflicts, mainly between farmers and cattle herders, over the limited water left from the lake and now a drought is drying it up more and the fight over water has worsened” says Adenike Oladosu, a wetlands conservation activist in Nigeria.

Rio Negro

The Rio Negro is the largest wetland protected under the 1971 Ramsar Convention on Wetlands

Barron Joseph Orr, chief scientist with the United Nations Convention to Combat Desertification, says wetlands are often resilient ecosystems, but prolonged drought is now a growing threat.

“Climate change projections show increased drought intensity in drylands that could affect wetland resilience and reduce important habitat services,” he says.

In other areas too, drought can damage wetlands, but the beaver can help protect them. There are already more than 100 successful reintroduction projects in North America and northern Europe.

In Europe it is believed that the population has tripled in the last 20 years, according to Professor Willby, and beavers are now re-established in most European countries. Sweden, Germany and Austria led the way, according to the Natural History Museum, but the UK followed in the early 2000s.

“The main motivation for bringing back beavers to the UK was mainly to help restore a species that was declining in its native range,” says Professor Willby.

“But its potential value as a key species for other biodiversity and in natural flood management was becoming much more attractive, and these are the arguments now usually put forward in support of local releases of trans- occupations or fencing trials that are taking place in many places. .”

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