Key points
- Scotland is expanding its woodland cover as part of its efforts to combat climate change and improve biodiversity. If this expansion happens at the expense of moorland habitats it could negatively impact open moorland species, such as mountain hares.
- This study focuses on the Cairngorms National Park (CNP) as a case study to assess how woodland expansion could affect mountain hare distribution.
- Researchers modelled hare presence under current and future woodland expansion scenarios, using models of species distribution.
- If 350 km² of new woodland is added by 2045, hare occurrence is expected to decline by 7% due to habitat loss and changes in land management.
- Modelled results indicated that declines in hare distribution were influenced by changes in land management (grouse moor management) more than the direct loss of moorland.
Background
Increasing woodland cover is widely promoted as a method of mitigating the effects of climate change and improving ecosystem resilience. However, where to place extensive new woodland without negatively affecting existing biodiversity is under debate.
Scotland’s government aims to increase woodland cover from 18% to 21% by 2032. Areas with deep peat soils, farmland, and designated conservation areas are less suitable for afforestation due to their economic and ecological significance. As a result, woodland expansion in Scotland mainly targets open moorland. Therefore, understanding how these habitat changes might affect moorland wildlife is crucial in evaluating potential trade-offs.
Open moorlands support internationally important ecosystems and species. Managed moorland also supports very high densities of mountain hares, where they are thought to benefit from grouse moor management practices, such as predator control and muirburn (controlled heather burning).
Spring counts show that managed grouse moors in northeast Scotland support exceptionally high mountain hare densities. These driven grouse moors, with more intensive management, sustain hare densities of 50 hares per km2. This is far higher than the 1-2 hare per km2 found in the less-managed landscapes of western Scotland.
The Cairngorms National Park (CNP) is a good case study for the potential effects of woodland expansion on mountain hares. Located in the northeast of Scotland and encompassing the Cairngorm mountains, the CNP is the largest national park in the UK at 4,528km2 in size. As the core range for mountain hares in Scotland, this area includes large areas of moorland, and grouse shooting estates that support high hare densities.
Woodland cover with the CNP is 1.6% lower than the Scottish national average, and the park authority aim to increase woodland cover by 350km2 (8%) by 2045. While the Cairngorm National Park Authority (CNPA) Forest Strategy promotes sensitive planting, large-scale woodland expansion will replace some areas of moorland. In turn, potentially displacing open moorland species, such as the mountain hare. This study examines the impact of this proposed change in woodland cover on mountain hare distribution.
What they did
Researchers used Species Distribution Models (SDMs) with mountain hare presence data from a 2006/07 survey of landowners, wildlife managers, hill walkers, and gamekeepers. The model was used to estimate the probability of mountain hare presence across the CNP under current and proposed woodland cover.
The study examined how woodland expansion could impact hare distribution under two scenarios. It simulated the effect of adding 70km2 of woodland by 2027 and 350km2 of woodland by 2045. Environmental factors like altitude, temperature and rainfall were incorporated into the model. Muirburn and grouse butts were also included as indicators of grouse moorland management. Two key assumptions were made:
- New woodlands would replace moorland first, as per afforestation policy.
- If woodland cover exceeded 33.4% in a 1km2 area, grouse moor management would stop. This cut-off was based on an assessment of the data on moorland management in relation to woodland cover.
What they found
Results indicated that mountain hare presence was significantly associated with moorland, and very strongly associated with managed moorland – specifically grouse moors – where indicators such as grouse butts and muirburn signify active land use for gamebirds. Additionally, the conversion of moorland to woodland was linked to a decrease in likelihood of mountain hare occurrence. These findings indicate that the most significant reduction in hare presence was tied to factors related to moorland management.
As a baseline, hares were predicted to occur in 74% of the CNP in 2006. However, under the 2045 woodland expansion scenario, which involves the creation of 350km2 of new woodland, hare occurrence is projected to decline by 7%. This equates to an estimated loss of hares from 246 individual 1km2 squares in the CNP.
The 2027 afforestation scenario, with a 70km2 woodland increase, is expected to have a smaller impact, with mountain hare predicted to disappear from 47 1km squares, or 1% of the park area.
Predicted declines in hare presence was most pronounced in the north and east of the park, where increased woodland cover is likely to be greatest.
What does this mean?
The greatest declines in mountain hare distribution were associated with the likely loss of managed moorland, largely due to woodland expansion. This expansion not only reduces moorland habitat but also diminishes its management, leading to a decline in suitable habitat for mountain hares. Since mountain hares are thought to benefit from traditional moorland management practices, the loss of management moorland likely poses the most significant threat to their populations.
Previous studies may have underestimated the impact of afforestation on hares by not considering the associated management changes. The response of hares to woodland expansion is complex and depends on factors like tree species, woodland management, and woodland maturity.
Young plantations could provide some benefits for hares, such as food availability. However, as trees mature and the canopy closes, this habitat will decline. Dominant tree species will also impact the woodland characteristics, and the shelter provided by the trees will influence the use of the habitat by mountain hares. Natural regeneration of woodland might be less damaging to mountain hare populations, as the more diverse flora and tree ages associated with naturally regenerating woodland would better support them.
Woodland expansion in the uplands will likely increase moorland fragmentation. This could further disrupt mountain hare populations because they have limited dispersal capacity. Fencing designed to protect new woodlands from herbivores like rabbits, hares, and deer could worsen habitat fragmentation for hares in afforested areas. It will restrict their access to both the woodland and large areas of heather moorland.
Mountain hares were relatively recently granted full legal protection. However, their control is still permitted in circumstances such as protection of crops and timber. If the licensed hare control for the woodland expansion was extensive, this could pose a threat to mountain hare populations. This would be especially damaging in the situation where control occurred in tandem with the change in land cover and land management associated with woodland expansion.
This study’s results could apply to other causes of change in moorland management. Economic shifts, including carbon trading, reduced interest in grouse shooting, and rewilding initiatives, will decrease moorland management. Predators are likely to increase, both in number and in distribution due to changes in land use and predator control, further threatening hare populations.
This case study highlights the crucial relationship between managed moorland and mountain hares, a species of open moorland. Woodland expansion can negatively impact open habitat species, both directly (through loss of habitat) and indirectly (through loss of associated management). Balancing woodland expansion with conservation needs for these species is essential.
Read the original abstract
Newey, S., Hubbard, C., Gibbs, S., McLeod, J., Smith, A., & Ewald, J. (2024 online early). The distribution of mountain hares and the possible effects of woodland expansion using the Cairngorm National Park as a case study. European Journal of Wildlife Research. 70-72: 1-13