Scotland’s lost mountain woodlands could make a comeback — but only if deer populations are brought under control, according to new research.
A six-year study examined how deer management affects upland habitat and found that high deer densities severely limit the survival of dwarf birch, a native species crucial to restoring mountain woodland.
Scotland’s Highlands have some of the highest deer densities in Europe — driven by centuries of land management for sport and the absence of natural predators.
Mountain woodlands provide vital benefits, including stabilising slopes, reducing landslide risk, and cutting downstream flooding.
The research, led by PhD researcher Sarah Watts from the University of Stirling’s Faculty of Natural Sciences, revealed that when red deer numbers exceed three per square kilometre, dwarf birch planted in grassland and heath suffers heavy browsing and high mortality.
At lower densities, survival rates improve dramatically, with growth strongest in heathland.
Ms Watts said: “These findings show that blanket bog is a refuge where populations of dwarf birch have escaped overgrazing, rather than providing the ideal conditions for planting and restoration action.
“This means that Scotland’s lost mountain woodlands can return more widely if deer densities are reduced.”
She added: “Instead of being an unspoilt wilderness, the Highlands have been influenced by people for thousands of years.
“Scotland has some of the highest deer densities in Europe, due to management for sport shooting and the removal of top predators such as wolves and lynx.”
Current national targets allow up to 10 deer per square kilometre, but local figures range to more than 64 — far too high for sensitive upland habitats, the study warns.
Ms Watts said: “Deer are an essential, celebrated part of our natural and cultural heritage. But action to address this imbalance would promote more sustainable, healthy deer populations, facilitate the recovery of other iconic woodland habitats, such as Caledonian Pinewoods and Atlantic Rainforests, and boost the general condition and diversity of our uplands.”
The study, supported by Forest Research, involved planting 750 dwarf birch trees across three Highland sites — Ben Lawers, Corrour Estate, and Glen Finglas — under varying grazing pressures. Over 40,000 measurements were recorded during the experiment.
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Co-author Dr Nadia Barsoum, Senior Biodiversity Scientist at Forest Research, said: “Our native shrub and tree species have evolved and adapted to specific environmental conditions over millennia, making many of them specialist survivors able to thrive where other species cannot.
“Uniquely placed then are these species to deliver ecological and ecosystem benefits in these contexts like no other. Giving ‘space for nature’ in the case of dwarf birch has a tangible remedy as this study demonstrates.”
She added: “Deer management will allow this native tree species to escape the confines of their final refugia and reclaim large areas of the Highland uplands, bringing back all the evolved benefits that have been lost.”
Ms Watts concluded: “Tree planting is best targeted in suitable habitats when seed sources for natural regeneration are lacking. However, it is necessary to address the original causes of habitat loss, particularly overgrazing, with landscape-scale management for a lower density red deer population (below three per km²) being key to facilitating the recovery of mountain woodland. We therefore need to increase rural employment and promote the value of jobs such as deer stalking for supporting nature recovery.”
“Dwarf birch regenerates particularly well in heathlands without the pressure of overgrazing, but such mountain woodlands are exceptionally rare in our Highland landscapes shaped by centuries of land-use and grazing management. These habitat mosaics are not typically recognised in protected areas or conservation policy.”
“Our research illustrates the value of an outside the box, or in the case of dwarf birch, thinking outside the bog, approach to conservation management — encouraging us to work outside of habitat refugia, small tree planting projects constrained within fences, and static vegetation categorisations which omit mountain woodland mosaics.”
“Reviving mountain woodland mosaics will tackle biodiversity loss and help mitigate climate change impacts on a national scale.”
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