Mountain birch genetics and recovery in Scotland

Summary Description:

Globally, around two in five plant and fungi species are threatened with extinction as result of increasing pressure from habitat fragmentation, emerging pests and pathogens, and climate change. Montane woodland habitats in Scotland have undergone extensive anthropogenic degradation and fragmentation in recent centuries; this is of great significance given their intrinsic biodiversity value and the associated services they provide, such as the potential to mitigate the impacts of climate change, acting as a habitat refuge for rare species, stabilisation of slopes, and their vital role in flood mitigation.

Birch is a key component of montane woodlands in Europe, along with willows. In Scandinavia where mountain woodland is widespread, progression towards the altitudinal treeline reveals a gradual transition from silver birch to downy birch and dwarf birch. In contrast, mountain birch in Britain is mainly found in tiny, scattered and fragmented populations of downy birch in upland locations across Scotland, often with dwarf birch, and introgression between the two species is common. Historically, the distribution of mountain birch may have been more extensive in Britain, prior to divergent land-use histories compared to Scandinavia – however the extent to which this occurred remains unknown.

Genetic diversity underpins the resilience of forests. It is key to the survival, adaption and evolution of species under changing environmental conditions. In Scotland, assessment of neutral genetic diversity in montane willow and dwarf birch has provided useful knowledge for restoration; however, further work is required on high altitude downy birch.

By studying how differentiated populations of the remaining Scottish mountain birch stands are in terms of their neutral genetic variation, we can explore whether this habitat may have been more widespread and contiguous in the past. This knowledge will inform land management regarding the need, or otherwise, to improve genetic connectedness.