Can trees prevent landslides like the Rest and be Thankful?

They are already escalating. The infamous Rest and be Thankful has already had millions on landslide mitigation measures, and is set to have £470 million spent on the "debris-flow" shelter  viewed as the long-term solution for protecting the road.

But, says parks campaigner, Nick Kempe, the landslide problem is much bigger than this gateway road. The eight landslides that swept the A83 at Glen Kinglas, just the other side of the hill from the Rest and Be Thankful, he has written, represent "twenty years of government failure".

 Kempe, who writes the parkswatchscotland blog, first became interested in landslides 20 years ago when he edited a book about Scotland’s mountain environment titled Hostile Habitats, but that concern intensifed in 2019, when a huge storm washed away part of the railway at Ardlui.

A keen mountaineer, he went out to witness the landslip and damage, and, as he explored the hills, “spotted over a dozen quite major landslips and realised that the ground was just falling apart”.

Is the Rest and be Thankful part of a wider problem?

Kempe thinks so. “I’ve written a bit on the Rest and be Thankful,” he says, “and I realised it’s part of a much bigger problem. It’s only just one bit and it’s like the one bit that the system has focussed on. But it was also that what was happening in response to the Rest and be Thankful wasn’t dealing with any of the fundamental issues.”

He believes that the chief problem lies in Scotland's land management – the way the lack of trees and grazing of land by sheep, cattle and deer, have left our slopes unstable. He also argues that we could learn a great deal from other European countries that tackled similar problems long ago.

READ MORE: Rest and Be Thankful. Scotland's landslide plan risks lives

READ MORE: Scotland floods: From A83 to swamped crops, what to learn?

Are there lessons to be learned from other countries?

“In the 19th century,”  Kempe says, “lots of European mountains were completely bare. They were degraded and overused as many of Scotland's mountains are. And what happened was terrible avalanches, which are very like landslips, which wiped out whole communities. Because of that, they decided to plant dangerous slopes to protect human infrastructure. Where they saw not just avalanches, but landslips too, they planted those slopes. Those forests that have grown up then regeneration through natural regeneration.”

He also points out that, in spite of what we know about how trees can stabilise soil and prevent landslides, there has so far been little use of planting for this purpose in Scotland. In the years since the 2004 landslides at Glen Ogle, Glen Kinglas and on the A9 north of Dunkeld, and the reports that followed,  little attempt has been made to apply trees to the wider threat of landslides.

 “The Rest and be Thankful," Kempe says,  "is basically as far as I know the only example of tree planting to prevent landslide.”

What tree-planting has been done at the Rest and be Thankful?

Last year, following purchase of the land, Forestry and Land Scotland, started planting trees on the steep southwestern flanks of Ben Luibhean above the A83 trunk road, at the head of Glen Croe. Since the slopes are so unstable and challenging, the project has involved novel techniques, including a trial of seed-delivery by drone.

What about other sites with high landslide risk?

For Kempe,  it is not just a question of the Rest and be Thankful. “Why aren’t we planting elsewhere? People were talking about tree planting at the time of the Scottish Road Network Landslides study in 2008.”

Glen Kinglas, which last month saw those eight landslips, has not received the same attention as the Rest and be Thankful, but it has had some mitigation work. In 2013 BEAR carried out a study and recommended "linear catch ditches and bunds", but not forest-planting, though it was considered. Those bunds, a form of embankment, were constructed in 2019.

"While planting of trees," Kempe writes, "is not a panacea for landslips, if done with care it potentially offers a cheap and effective solution.  Had some trees been planted on these slopes immediately after the events of 2004 that might just have prevented some of those six landslips or stopped them reaching the road."

He notes that not only did planting not occur on the Strone estate, the site of many of these landslides, but the landowner was given permission on several occasions to fell the small plantations alongside the A83.

Are there other land management issues?

Also linked to this issue of lack of trees is the way land in Scotland is used for grazing - and the link between that, too, and landslides has been flagged for some time.

 Back in 2013, George Monbiot wrote a column titled Sheepwrecked, in which he quipped that the Rest and be Thankful would better be described as the “Get The Hell Out Of Here”.

“One of the factors destabilising the soil,” he noted, “is the presence of sheep on the hillside. A report the government commissioned notes that the sheep make landslips more likely because they compact and erode the soil and prevent trees and shrubs (whose roots might otherwise have fixed the slope) from growing.”

Even now, Kempe observes, both cattle and sheep are still grazing on some of the landslide-prone slopes around the A83 ( his blog provides evidence of subsidies given to landowners in the area).

What do scientists who have studied landslides say?

According to a world expert on landslides, Professor Dave Petley of University of Hull,  it's hard to know whether trees, had they been planted decades ago, would have made a huge difference at the Rest and be Thankful. 

"I don’t think," he said, "we can be definitive either way – this is complex topography and the rainfall pattern is shifting.  At a national level, trees are an important aspect of landslide prevention.  They absorb water, they prevent erosion, they manage drainage and their roots hold the soil together.  So, whilst we cannot say for certain that trees would have made a difference at Rest and Be Thankful, we can say that ensuring that there are more trees across upland areas of Scotland will be a key aspect of reducing landslides."

Neverthless, Professor Petley backs the need for nature-solutions as part of the answer to the wider problem. "We should be trying to use nature-based solutions, as these are effective and bring other benefits, for example to biodiversity.  But we also need to recognise that conventional engineering solutions will be necessary in many cases, not least because of the immediacy of the threat.  For example, once land has become unstable it can be difficult for trees to become established.  On the whole, woodland needs to be planted before landslides have developed."

What other sites are at landslide risk?

Though there have been reports like Scotland, a full mapping of Scotland for landslide risks not just to road, but also railway and other infrastructure has been done. 

 The recent landslide at a new site, near Ardfern on the A816,  which has never previously experienced one, is a reminder of the need for further research - looking into both where the risk is and how we can mitigate it, ensuring that security of access and connection for communities.

The Scottish Road Network Landslides study listed 67 road sections as priority sites. Each stretch was given a hazard rating and the very worst with scores of over 250 were the A82 at Loch Lochy and the A85 at Glen Dochart. The Rest and be Thankful at and Glen Kinglas both scored 180 and came in at 12th and 13th on the list. The A816 was not mentioned in the report at all.  

This further mapping of landslide risk is an element of what Nick Kempe is calling for.

A816 landslide at Ardfern. Image: Gordon Turner

Is the Scottish Government dealing with this fast enough?

Kempe observes that land management change, and more trees on such slopes, is needed at speed if there are not to be more Rest and be Thankfuls. 

“We need,” he says, “a much quicker process now. And if landowners won’t sign up to removing grazing and planting trees on slopes where planting trees might help – then possibly we need to compulsorily purchase land.

"With the Rest and be Thankful it’s been a very painful process and if they’re going to have to do that 50 times across Scotland, it just doesn’t bear thinking about. It’s crazy not planting trees. Because planting trees is cheap compared to civil engineering.”