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Friends with benefits? Beavers and aspen keep life complicated

Friends with benefits? Beavers and aspen keep life complicated

The synergy between beavers and aspen reminds us that nature recovery cannot be achieved one species at a time. We need to be willing to let nature lead, embracing the marvellous complexity that wildness generates.

Words by Hugh Webster

Images by SCOTLAND: The Big Picture

After an absence spanning centuries, beavers are back; recently turning up just upriver from where I live, in the headwaters of the sprawling Tay catchment. Here, the River Ardle emerges from a wide expanse of open moorland, where a few downy birches poke out defiantly. Since the beavers’ return, however, most of these hardy pioneers have been felled. In an area with just a handful of riverside trees, the beavers’ impact appears devastating.

But these toppled birches are not dead. Their conical stumps are already coppicing, promising to turn what were leggy, isolated trees into dense, bushy thickets. And just a few hundred yards downstream, the riverbanks are still crowded with birch and alder – despite the proximity of beavers. It’s easy to imagine that, were these busy wetland engineers re-establishing themselves into a more naturally forested river catchment, their impact would feel quite different. In our human-modified landscapes, however, their return poses questions.

Beavers have recently been reintroduced to Speyside, making a welcome return to Scotland’s largest national park. But amid the widespread celebrations, concerns have been expressed about their potential impact on riverside trees. This is particularly true of aspen, which should be common across Scotland, but surviving stands have become scarce, widely separated and struggling to reproduce. Against this backdrop, people are asking: can the return of beavers and the recovery of aspen be achieved concurrently?

Aspen is highly valued because it supports a great wealth of biodiversity, and the Spey catchment retains more aspen woodland than anywhere else in Scotland. However, these trees are also valued by beavers, with their larger limbs used for dam and lodge building, and the highly palatable leaves – which are appealing to many species – a favourite food. With one third of Speyside’s aspen woodlands considered accessible to beavers, it is here that coexistence between these two recovering species will soon be tested.

Happily, while beavers enjoy eating aspen, their activity also offers myriad benefits to aspen-dependent species and even the tree itself. The Park Authority’s Forest Strategy notes that, at present, many aspen stands are ‘over mature and have no young trees to replace them.’ By felling these older trees, beavers stimulate coppicing and suckering, the process by which new saplings spring from the existing root stock, and thereby diversify the structure of ageing stands. This regrowth can then help species like the dark-bordered beauty moth, the larvae of which depend on young aspen suckers.

Furthermore, by building dams and excavating a network of foraging ditches, beavers work to expand wetlands and raise groundwater levels, thus increasing the extent of suitable aspen habitat. Their foraging is also largely concentrated around their lodges, meaning that their impact is intrinsically patchy – dramatic here, but barely noticeable over there – and the resulting habitat mosaics naturally boost biodiversity.

Even more excitingly, beavers could help restore connectivity between fragmented stands of aspen woodland. For reasons that are not yet fully understood, aspen trees rarely produce seeds in Scotland. Instead, they mostly reproduce by cloning, sprouting new trees via the spread of suckers. This works well enough where browsing pressure is not too high, but it imposes limits on how far young trees can spread from their parents. Wider dispersal requires the mobility of a seed, and this is where beavers can help.

Aspen (Populus tremula) trees in autumn displaying bright yellow foliage, Insh Marshes, Cairngorms National Park, Scotland, October
Aspen (Populus tremula) trees in autumn displaying bright yellow foliage, Insh Marshes, Cairngorms National Park, Scotland, October

The gnawing attention of beavers is thought to stimulate aspen seed production. Experiments show that where beaver gnawing is replicated artificially, trees become stressed and are ‘tricked’ into producing seeds. Indeed, in Norway, aspen has recovered much of its former abundance alongside beavers, and here seed production usually occurs annually, yielding up to 80 million seeds per tree. While there may be climatic factors that encourage seeding in Norway, if aspen and beavers can coexist in Scandinavia, then why not here?

Where concerns surround individual trees and unique assemblages of rare lichens and bryophytes, safeguards can be employed, using fencing or beaver-proof mesh. Indeed, this approach was adopted successfully in Knapdale where a few trees hosting a particularly rare lichen were identified and protected. Ultimately, rewilding cannot be about conserving one species at a time. Instead, rewilding asks us to return nature its freedoms, to embrace uncertain outcomes and celebrate all the richness that dynamism can create.

As beavers settle back into the Spey catchment, reoccupying a landscape that has long been recognised as having the most suitable beaver habitat in Scotland, they will begin to reassert their unique influence, revitalising natural processes along the river, creating vibrant wetlands and adding deadwood structures into watercourses – all things that conservation bodies have long spent time and money trying to replicate. Beavers do this work for free. Most of the time, they do it better.

Beavers could also encourage more nature-friendly landowners to plant and protect aspen, especially where they anticipate beavers are likely to return. Aspen is a fast-growing pioneer species, but it is also an all-or-nothing species, which means that either a lot of its suckers tend to get away, or none do. Put simply, the more aspen there is, the better its chances of tolerating browsing pressure and thriving alongside beavers. So, if people are really worried about the future impacts of an expanding beaver population on the prospects for recovering aspen, they should be out there planting and protecting as much aspen as possible today, playing their part in #PaintingScotlandYellow.

Nature is complicated, or at least it should be. In our simplified and frequently impoverished landscapes, it can be easy to forget that, in more natural ecosystems, complexity is everywhere. We need to remember that the ‘troublesome’ beavers felling mature aspens are the same ones stimulating regeneration, boosting biodiversity, encouraging seeding events and enabling the spread of wet woodland habitat. Beavers and aspen have a complex relationship, part exploitative, part synergistic, but that complexity isn’t a problem, quite the opposite. In truth, that’s the beauty of it!

Main image: European beaver (castor fiber) swimming across forest lochan, Knapdale Forest, Argyll, Scotland. Credit: SCOTLAND: The Big Picture