Endangered mountain trees making a comeback in Scotland, study shows

Endangered mountain trees and shrubs are making a comeback in Scotland, mitigating the effects of extreme weather, a study by the University of Stirling has shown.

Montane scrub provides protection from flooding, avalanches, rockfalls and landslides, as well as supporting a range of rare insects and scarce birds.

Overgrazing by deer and sheep on Scotland’s peaks since the 18th century contributed to a rapid decline in high-altitude woodland. By the 1990s native montane willows were nearly extinct, with the largest remaining patch equivalent to the size of a tennis court.

Since then, almost 400,000 montane willows have been planted within 2,659 hectares managed for the restoration of mountain woodlands across Scotland, bringing the trees back from the brink of extinction. 

The area these special arctic-alpine plants occupy has increased a hundredfold since the 1990s thanks to the efforts of conservation charities and private estates working on a long-term vision for nature recovery. 

A review of progress made over the last 30 years has been carried out by PhD researcher Sarah Watts, of the University of Stirling’s Faculty of Natural Sciences.

Reviving mountain woodland

Sarah said: “There is significant capacity for a high-altitude vegetation type that was nearly nationally extinct to make a comeback and flourish under conservation management.

“Reviving a mountain woodland mosaic shaped by regeneration will tackle biodiversity loss and help mitigate climate change impacts on a national scale.

“Montane scrub supports a vibrant community of insects including bumblebees, butterflies, moths, and over 20 rare sawfly species in Scotland that each rely on an individual species of arctic-alpine willow for their survival. The habitat also hosts upland birds that are scarce or declining elsewhere in Britain, such as the Ring Ouzel, a charismatic mountain blackbird.

“Mountain woodland also stabilises steep slopes and gives protection from the natural hazards of avalanches, rockfalls and landslides. It slows the flow of water over and within upland soils, facilitating a decrease in flooding downstream. These benefits are called nature-based solutions because they are considered vitally important for reducing threats from escalating climate change including more extreme weather.”

Sarah Watts measuring downy willow at Ben Lawers 

Sarah is Chair of the Mountain Woodland Action Group and has been working on montane willow scrub restoration since 2010, first as a volunteer with the National Trust for Scotland, then as an ecologist at Ben Lawers National Nature Reserve from 2013 until 2020. She began her PhD at the University of Stirling in 2019 and her previously published research mapped trees growing at the highest heights in Scotland. In the course of her work to find scarce trees atop Scotland’s highest peaks, Sarah has bagged more than 200 Munros. Sarah also set out the benefits of mountain woodland restoration in a paper published in 2022.

Her latest paper Montane willow scrub restoration in Scotland: reviewing 30 years of progress to reestablish the altitudinal treeline was published in Restoration Ecology, the journal of the Society for Ecological Restoration. The review looks at best practice across Scotland, featuring conservation efforts by environmental organisations including Trees for Life, Cairngorms Connect, RSPB, Borders Forest Trust, Corrour, Forestry and Land Scotland, and particularly the work led by the National Trust for Scotland. 

Sarah said: “The pioneering site for montane willow restoration in Scotland is Ben Lawers National Nature Reserve, owned and managed by the National Trust for Scotland. No other restoration project in the country is comparable in scale and longevity. 

“Here, widespread planting of 54,882 montane willows took place during 1998-2012. Over 110 hectares of montane scrub has now been restored at Ben Lawers, accompanied by an explosion of invertebrates, mammals, and birdlife. This site is undoubtedly the most biodiverse place in Scotland’s mountains.

“Mar Lodge Estate, also owned and managed by the Trust, has demonstrated outstandingly successful application of supplementary planting together with landscape-scale deer management; 5,797 montane willows planted here in 2021 and 2022 had a 100% survival rate during recent monitoring.

“These projects have inspired many others across the country, and also the careers of more practitioners and researchers such as myself. The review celebrates the huge contribution of the Trust’s staff and volunteers over decades to produce a thriving, vibrant altitudinal treeline with benefits to people and wildlife.”

Restored montane willow at Ben Lawers

Montane willow scrub is one of six habitats the National Trust for Scotland has prioritised in its Plan for Nature, announced earlier this year. In it, the conservation charity, which cares for 76,000 hectares of countryside in Scotland from coastlines and islands to mountains, makes it clear where it plans to focus its efforts to help nature flourish.

Jeff Waddell, Head of Nature Conservation at the National Trust for Scotland, said: “Montane willow scrub is one of our rarest habitats, with only a few hundred hectares remaining throughout Scotland. It supports a range of rare and scarce species, and it is one of the habitats where our work can make the biggest impact. 

“As Sarah highlights in her research, we have spent many years carrying out pioneering work to regenerate and restore this habitat at both Ben Lawers National Nature Reserve and Mar Lodge Estate National Nature Reserve. Nature needs to be protected now more than ever and our success so far in restoring montane willow scrub demonstrates what is possible when habitats or species are prioritised and given the opportunity to thrive.”

Restoration expansion

Sarah is hopeful that there will be an expansion of restoration on land managed for other purposes. She said: “As well as focusing on conservation areas, future action should harness the capacity for nature recovery on land previously managed intensively for sport shooting, which often host natural populations of montane willows in need of rescue and enhancement. 

“Through the progression of wider collaboration fostering habitat connectivity, montane scrub restoration should help deliver a sustainable future by reducing impacts of nature and climate emergencies on a national scale. Treeline reestablishment must be underpinned by management for low-density large herbivore populations to remove the pressure of overgrazing and enable a balance between sustainable numbers of animals and plant growth. 

“This vision would require moving beyond relatively small-scale projects held behind fences toward action at landscape scales. Enhancing rural employment and retaining invaluable skills in deer management will be fundamental for meeting this goal.”

Sarah Watts’ PhD is funded by the University of Stirling, Woodland Trust, Corrour Estate, National Trust for Scotland, Forest Research, Scottish Forestry Trust, Future Woodlands Scotland, and the Macaulay Development Trust.