THERE are plenty of places along the Tay and its tributaries these days where you see the work of beavers: pencil-tipped stumps stand next to cartoon trees teetering on a spindle, with piles of chippings left by chiselling teeth.

At the last count in 2017 more than 400 beavers, descended from illegal releases or escapees, were living in the river’s catchment, and they’re hard at work gnawing on trunks for food and lodge-building material.

But it’s difficult to understand the full impact of the animal, whose native population became extinct in Scotland nearly 500 years ago, until you see what they do on a landscape scale.

READ MORE: Tory MSP loses bid to block protection for beavers

The owners of the Bamff estate in Perthshire, which I visited in 2017, first kept beavers in an enclosure there in 2002, and since then the animals had bred and expanded their territory.

As a result, a small wooded valley drained by a narrow burn had become a beaverscape: ponds 50 and 70 metres long lined the valley, behind 20-metre wide dams of sticks and stones. Around the ponds, lush green turf was cut with beaver-dug channels, moats to defend their grazing spots.

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With the flooded remnants of the woods still reaching dead hands skywards, it reminded me of the aftermath of the Somme.

But looking closer I could see the dead trees and damp gnawed stumps were habitat for the richest of fungi and mosses. In summer, I learned, the soggy valley was abuzz with insects feeding birds and small mammals, which in turn feed foxes, owls and buzzards.

The reintroduction of “keystone species” that can change whole environments, as beavers had at Bamff, is vital to the idea of rewilding: the restoration of ecosystems that function without human management.

READ MORE: Beavers to be given legal protection in Scotland

Granting beavers protected status – as the Scottish Government will do on May 1 – makes this the first-ever legal, permanent reintroduction of a mammal to the UK.

Enthusiasts say species such as lynx and even wolves could eventually follow, apex predators to keep herbivores in check and complete the rewilding circle.

Though nothing will be formally reintroduced without lengthy debate, Alan MacDonnell of the eco-charity Trees for Life says: “We hope the success of the beaver population will make it easier to have those conversations.”

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But what exactly will we gain from beavers? Will they develop useful “eco-system services” as conservationists claim? Or is it what farmers fear: a giant experiment with our countryside, with no certainty of outcome, and the potential to disrupt vital food production?

One benefit of beavers is already visible: they’re a boost to tourism. At least one Blairgowrie operator – Bob Smith of Nature Nuts – provides beaver tours. It was with him I got a glimpse of a beaver in the River Isla in Perthshire in a freezing April dusk, and I came across a canoe-tour company in Alyth selling the chance to see beavers in the wild.

READ MORE: Beaver dams could help prevent flooding say experts

The main advantage, though, will be when dams on burns such as those at Bamff create those rich habitats, and provide a buffer to floods, retaining water instead of letting it rush down to lower ground.

The dams also filter water, catching sediment and pollutants. To do that, beavers need to get out of wide rivers such the Tay and the Earn, where they provide few benefits, and into the small burns.

Asking beaver enthusiasts how long that will take to achieve on a national scale is a bit like that piece-of-string question.

GOVERNMENT wildlife agency Scottish Natural Heritage (SNH) says their population on Tayside has been growing by 20% to 30% a year, meaning the 400 or so estimated to be here in 2017 has grown already to more than 600.

READ MORE: Farmers share concerns about impact of beaver population

There is also another centre of beaver population ready to expand across the country. While the Tayside population slowly grew from the early 2000s, the Scottish Wildlife Trust (SWT) and Royal Zoological Society of Scotland were lobbying for a licensed trial of beaver reintroduction The trial began in 2009, on a forested site at Knapdale in Argyll. Some from that original population survive, and they are currently being boosted by further licensed reintroductions, so there are now perhaps two or three dozen animals there.

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The Government has said new reintroductions will not be permitted for now – the animals must spread naturally – but there are significant natural barriers, especially across the Highlands.

Gill Dowse of SWT says the trust would be “quite keen” on further licensed releases, perhaps in the north-west, once the rules which will allow land managers to control problem beavers have bedded in.

But she believes the way SNH acts in running that beaver control system is key: a liberal attitude to handing out culling licences could keep numbers too low for the spread into hill country to happen.

READ MORE: Support for proposed return of beaver species to Scotland

‘‘The more they are allowed to recolonise areas and be where they want to be, the more they are allowed to travel into upland areas, the more benefits we will get,” she says.

For her, like MacDonnell, beavers are “absolutely” part of the rewilding agenda, and she agrees they will fuel more reintroduction plans.

But she admits we can’t always know what will happen: “SNH has gone through very complicated habitat suitability monitoring programmes, but the beavers haven’t read that, so there will probably be unforeseen consequences,” she says.

I’m reminded of a recent conversation about Scotland’s most notable wildlife reintroduction so far. Sea eagles, brought back here in 1975, now number more than 200, and farmers near Oban were complaining the enormous birds were killing lambs, but an SNH official told me lamb predation had not been predicted when the birds were reintroduced.

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The last of the native sea eagle population was shot in Scotland in 1916: they were hunted with a vengeance during and after the Clearances, when sheep took the place of people in the Highlands.

If we forgot there can be a problem with sea eagles and sheep in a 59-year-gap in their presence, what have we forgotten about the impact of beavers, after a much longer gap?

A BEAVER lodge has already been found in a culvert on a housing estate, and to deal with the random spread of beavers and such unexpected consequences, Dowse says SNH must be resourced properly.

On that, at least, conservationists agree with the farming community.

The Tayside beavers started appearing in the early 2000s. Arriving through escapes, or illegal deliberate releases, they couldn’t have been in a better place to stir conflict with agribusiness.

While Bamff is in the hill country that runs into the Cairngorms, to the south is some of the richest farmland in Scotland around the Tay, and tributaries the Ericht and Isla.

The flat land is kept dry for crops and machines by ditches and drains, but beavers can’t tell the difference between a burn and a ditch, and will dam the latter just as readily as the former to provide a haven for themselves and their young.

On the rich land around the lower Isla, I’ve seen soggy fields, beaver-dammed culverts and farmers despairing: it costs thousands of pounds a year to remove dams and deal with the flooding they cause.

As a result, the National Farmers Union Scotland (NFUS) put up fierce resistance to protected status. Environment Secretary Roseanna Cunningham declared in November 2016 that beavers would be protected, and most of the delay in bringing in protected status since then has been caused by the union saying ways for dealing with beaver problems must be fully trialled first.

SNH has now produced a two-tier code for tackling issues with the herbivores. Removing new dams, fencing areas off and reinforcing river banks can be done when and where a farmer wants. Digging out dams more than a fortnight old, destroying lodges, trapping beavers or shooting them can only be done with a licence, which SNH says will be issued as a last resort.

Andrew Midgley, the union’s environment policy manager, believes the beaver issue has damaged the case for rewilding: “The establishment of the beaver population in Scotland is an example of how not to do it,” he says.

But it’s clear in my conversation with him that anger from farmers has changed to cautious acceptance.

Key for Midgley is practical application of the new rules: how flexible SNH managers will be and, as Dowse also says, whether SNH can help farmers prepare for their arrival in advance.

Midgley fears a cash-strapped agency won’t be able to cope, and it reminds me that we already struggle to manage our red deer population. Add dealing with another large herbivore – adult beavers are the size of a tubby spaniel – to the list of SNH chores, and it’s easy to imagine the agency floundering.

Midgley says: “Some people think what we have been talking about is minor and won’t be a big deal: our expectation is it will be very significant, and a lot more significant than a lot of people think.

“One of our concerns was there wouldn’t be enough money from Government to deliver what we thought would be needed, and we are still in that area, I think, where there probably isn’t going to be enough money to deal with the problem.”

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THE Tayside experience has shown what will happen in the most productive farmland, and the Knapdale trial showed what happens in rough, forested land, but Scotland has plenty of farms in hill country, and it may be there that unexpected consequences of beaver colonisation appear. It’ll all be down to robust, sensible attitudes from SNH: not caving in to farmers but understanding centuries of land management can’t be altered overnight to accommodate rewilding.

That’s where Dr Ben Ross comes in. He is SNH’s beaver project manager, and when I talk to him he emphasises the need for balance in a situation which is less than ideal.

No studies have been completed yet to model the possible spread of beavers, but he says management to help farmers should have little impact on it, and encouraging the spread is one of the specific aims of the SNH regime.

He is also clear there are extra resources – understood to be several hundred thousand pounds a year for the next three years – being put in to SNH, mainly to develop “mitigation measures” to keep beavers away from the best farmland.

Devices such as mesh barriers in streams can be used to deter beavers, but physically removing and relocating them is fraught with problems. It can seriously stressful for the animals and it will be difficult to find sites where beavers can be legally released, so Ross says some beavers will inevitably die.

“Farmers have real, legitimate concerns and we’ve got in place a system – the backstop of this is the ability to carry out lethal control and we accept that it will happen,” Ross says.

He adds: “The headline message with all of this is that you balance conservation needs with the needs of the rest of society. It’s about coming up with solutions for the issues that will arise.”

I’m proud that Scotland is leading the way here: while trials have also gone on south of the Border we are the first part of the UK to give beavers native animal status and let them to spread naturally. But there will be challenges.

Whether animal lovers like it or not, some beavers will be shot, just as we have to shoot red deer to prevent environmental damage they cause. SNH has been burdened with yet another set of issues to manage, and giving it the resources to cope is crucial.

But despite the challenges, the hope of a better environment that the return of beavers represents inspires me.

As another SWT officer, Susan Davies, told me during the prolonged debate over protected status: “It’s about a moral obligation to return something that has gone through human interference.”

We know we can’t go on drawing from the planet without putting something back, and by allowing beavers to flourish, we are literally doing just that.