The appearance of beavers on a Devon river—and experiments with controlled reintroductions in Scotland and Wales—have brought the toothy rodents into the spotlight. They’re certainly fun to spot, but are their engineering abilities a boon or a curse? Two passionate countrymen put the case for and against.

Yes

Derek Gow, ecological consultant and water-vole breeder

Beavers are a well-studied species: where they conflict with humans, pragmatic solutions—including lethal control—are established. Beavers are not a wilderness species; they’re found around major European cities. Their impact in intensively settled arable landscapes can be significant, although tolerable, but where grazing predominates and river systems are wooded, they are generally of little concern.

The case for restoration rests on evidence that the habitats they create are of critical importance to other species: the biomass of invertebrates, amphibians and fish can be considerably greater where beavers exist.

The demise of the UK beaver quite probably resulted in the extinction of other native species, such as the large copper butterfly, whose caterpillars depend on the water dock that grows on wetlands where willow is coppiced; when coppicing, which mimics natural beaver activity, ceased, they became extinct. This ancient dependency, from beaver burrows in peat landscapes releasing bank sections that float out and create nesting habitats for grebes and divers to coppicing, is likely to apply to other native species, such as the water vole.

There is evidence that beaver-generated landscapes in the upper reaches of river systems can provide key ecosystem services. Their mosaics of small, linked wetlands play a role in carbon capture, the stabilisation of groundwater levels, aquifer recharging and silt or chemical retention. Beavers function as natural regulators of flow. An Environment Agency project at Belford in Northumberland shows that a combination of ‘natural’ features—field-corner pools, leaky dams and woody debris—has provided effective flood relief for the village. These features mimic the natural activities of beavers. The difference between beaver and human landscapes is that beavers provide a constantly rising level of structural diversity, but ours are limited to the maintenance of what we create. The interactions between beaver dams and migratory fish are complex.

Many dams are temporary structures that degrade naturally and there is evidence that game fish can easily pass through them. In a recent report, a Norwegian salmon manager stated: ‘The preponderance of evidence so far is that beaver dams benefit salmonids.’ The idea that dams are impenetrable barriers to migration is simplistic. There is no reason why the small breeding population of beavers on the River Otter should be extinguished.

The process of beaver recolonisation between isolated river catchments is very slow; they seldom forage more than 100ft from the water’s edge. In 1188, Giraldus Cambrensis, a traveling ecclesiastic, recorded seeing beavers on the River Teifi: ‘The church, mill, bridge and salmon leap, an orchard with a delightful garden, all stand together on a small plot of land. The Teivi being the only river in Wales which has beavers.’

The landscape described by Cambrensis is not a wilderness. If its inhabitants harvested salmon, it is likely that they also harvested beaver.

There is no credible reason why this 1,000-year-old vision of a richer environment could not be a tangible reality in the 21st century.

No
Mark Lloyd, chief executive of the Angling Trust

We warmly welcome Defra’s commitment to capture humanely and return to captivity a number of beavers that have found their way into the River Otter in Devon. As the national representative body for angling, we have been campaigning against moves to introduce beavers to England for several years because of the damage that they can do to rivers, riverside trees, fish migration and the potential spread of the tapeworm Echinococcus multilocularis, which can spread to dogs and humans, for whom it can be fatal.

Although beavers were native to some parts of the British Isles more than 500 years ago, our rivers have changed dramatically in the past five centuries and suffer from endemic pollution, over-abstraction of water and the presence of tens of thousands of manmade barriers to fish migration.

Nearly all fish species need to migrate up and down rivers in order to complete their lifecycle and the addition of beaver dams would only increase the number of obstacles that fish have to overcome. If we remove all these barriers to migration, then beavers present less of a problem to fisheries.

In a healthy natural ecosystem, beavers can actually be beneficial because they introduce woody debris to rivers and their dams can trap silt and create new habitats. However, fewer than 25% of the rivers in England and Wales are in good ecological condition and the Angling Trust’s view is that it would be irresponsible even to consider reintroducing this species into the wild without first restoring our rivers to good health by tackling low flows, pollution and removing the vast majority of manmade barriers to fish migration. Evidence from North America and Germany shows the considerable risk to infrastructure—including flooddefence assets, roads and railways— from allowing beavers to become established in high-risk and populated areas.

An adult beaver can bring down a 10in-wide tree in under an hour and a single beaver family will fell up to 300 trees a year. In the upper Danube region of Germany, beavers have caused £5 million worth of damage.

How will riverside residents feel when the only tree in their garden is gnawed down overnight? Or a beaver dam floods a housing estate that has never before flooded? The problem with beavers is that they’re very secretive, mainly nocturnal and they don’t stay put, so they’ll spread from rural areas to villages and the edges of towns and cities.

If it’s decided, democratically, to reintroduce them, having rescued our rivers from their dismal condition, and after a full debate about all the impacts they will have, then so be it. However, beavers should not be released illegally by enthusiasts who believe they can take a unilateral decision on behalf of the whole nation. We’re pleased that the Government has announced that it has no plans to license any beaver releases.

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* This article was first published in Country Life Magazine on July 23 2014