Montane willow scrub restoration in Scotland: reviewing 30 years of progress to reestablish the altitudinal treeline

Abstract

Many mountain woodlands across the globe have undergone anthropogenic degradation with negative implications for the ecological and socioeconomic systems dependent on them. Montane willows are arctic‐alpine species of high nature conservation concern within the altitudinal treeline. Scotland has been pioneering the restoration of montane willow scrub for three decades following widespread loss linked particularly to overgrazing by sheep and deer since the eighteenth century. In the 1990s, the total area of montane willows throughout the country was less than 10 ha, with most remaining populations highly fragmented, in rapid decline, and restricted to inaccessible cliffs. Subsequently, montane willow scrub restoration has been part of an overall 2659 ha area managed for the recovery of mountain woodlands in Scotland. By May 2023, 396,868 montane willows were planted in projects encompassing large‐scale habitat creation, relict population reinforcement by genetic rescue, fencing, and landscape‐scale management for low‐density deer populations. This review summarizes restoration methods and outcomes with case study examples to promote conservation evidence and research on plant growth and survival, planting sites, associated biodiversity, molecular ecology, genomics, and long‐term population sustainability. With the potential for montane scrub restoration to be widely expanded, improved connectivity to revive a treeline mosaic shaped by regeneration will tackle biodiversity loss and help mitigate climate change impacts on a national scale. However, caution must be applied to creating definitions of distinct habitats for restoration that are based on non‐natural or ecologically degraded systems. These experiences are particularly relevant to montane and circumpolar regions with strongly modified landscape histories.