Risk/opportunity:(from the Climate Change Risk Assessment for Scotland 2012):
BD11: Generalist species more able to adapt than specialists
Narratives: Tracking suitable space in a changing climate
SCCAP theme: Natural environment
N1: Understand the effects of climate change and their impacts on natural environment
N2: Support a healthy and diverse natural environment with capacity to adapt
N3: Sustain and enhance the benefits, goods and services that the natural environment provides
Snow-bed specialist bryophytes
- Generalist species are likely to be less at risk from climate change than specialist species that require specific ‘niche’ habitat
- Snow-bed bryophytes are specialist montane species that are threatened with a loss of climate space as they are already at the edge of their range in Scotland
- Projected long-term reduction in snow-lie is likely to see these species being replaced by more generalist montane vegetation
- Consistent trends have not been identified across snow-bed bryophytes
- An analysis of vegetation structure indicated a decline in snow-bed bryophytes in western areas but an increase in the east (Cairngorms), suggesting that structural change is occurring in snow-bed vegetation
Vegetation found in the Scottish mountains includes species of mosses and liverworts (bryophytes) which are snow-bed specialists dependent upon the late-lying snow which occurs in these areas. These ‘snowbed bryophytes’ include species of conservation priority such as Andreaea nivali, Marsupella arctica, and Gymnotrium apiculatum.
Information on the status of snow-bed bryophytes can be used to understand the risk that generalist species may be more able to cope with climate change than specialist species. This is because snow-bed bryophytes occur at the edge of their range in Scotland, capturing a situation in which species are unable to track changing climate space, e.g. via inter-connected habitat.
It is expected that a long-term trend towards a reduction in the size and length of snow-lie will cause changes in the composition of snow-bed vegetation; with conservation-priority snow-bed vegetation communities expected to shift towards a widespread ‘generalist’ vegetation type typical of more open montane conditions.
A comprehensive survey of snow-bed vegetation was carried out in 1989-1990, for 58 areas of late-lying snow across Scotland. Scottish Natural Heritage commissioned a repeat survey of 22 of the original 58 snow-beds during 2007-2008 (Fig. 1, Table 1); these were located across western and central mountain ranges, and within the eastern and relatively more continental Cairngorm Mountains. Analysis of the composition of bryophyte assemblages and the frequency with which species occur has demonstrated only very tentative evidence for change in snow-bed communities. This included a statistically significant 13% decline in the frequency of the snow-bed specialist liverwort Moerckia blytii. However, trends in frequency of occurrence were not consistent across the snow-bed bryophytes, with some species showing a decrease (e.g. Kiaeria starkei: -4%) and some an increase (Polytrichum sexangulare: +11 %).
A separate analysis for this indicator focussed on broad measures of vegetation structure: vascular plants, with grasses as a specific example, and bryophytes generally, with National Vegetation Classification (NVC) snow-bed bryophyte species as indicators. The analysis (see Fig. 2) demonstrated a decline in the frequency of NVC snow-bed bryophyte indicator species and bryophytes generally for the snow-beds in western areas, implying structural change in the vegetation. In contrast, snow-bed bryophytes and all bryophytes increased across the snow-beds in eastern Scotland. There is therefore preliminary evidence for a change in the snow-bed vegetation, which may show regional variation.
Ben Wyvis, North Coire
Mam Sodhail, Lochan Uaine
White Mounth, Coire Boidheach
White Mounth, Glas Allt
Creag Meagaidh, West Coire
Ben Lawers, An stuc
Ben Lawers, NE Face
Cairngorm, Ciste Mhearad
Carn Lochan, Coire Domhain
Carn Lochan, Coire Domhain
Ben Macdui, Lower Garbh Uisge Beag
Ben Macdui, Upper Garbh Uisge Beag
Ben Macdui, North Slope
Ben Macdui, Upper Garbh Uisge Mor
Ben Macdui, Bealach 1232m
Braeriach, Garbh Coire Mor
Braeriach, Garbh Coire Mor E Gully
Beinn a Bhuird, Coire an t’Snaechda
Beinn a Bhuird, Dubh Lochan
Beinn a Bhuird, North Top
Beinn a Bhuird, Garbh Coire
Table 1: Names of snow-bed sites used in the repeat survey(illustrated in Figure 1).
Fig. 2: Change in the frequency of snow-bed vegetation: time-series comparison (1989/90-2007) in the percent cover of four vegetation parameters – (i) grasses, (ii) all vascular plants (including ferns), (iii) NVC snow-bed dominant bryophytes (Kiaeria starkei, Polytrichum alpinum, Polytrichum sexangulare and Racomitrium heterostichum), and (iv) all bryophytes.
There are as yet no clear trends in the frequency of occurrence for snow-bed bryophytes, compared to more generalist species found in snow-bed vegetation communities. However there is some tentative evidence that suggests a reorganisation of snow-bed vegetation structure may be occurring but that this differs across regions in Scotland. On the other-hand, the evidence may reflect the fact that the repeat sampled plots were not strictly replicates.
As noted above, the sampled plots in 2007/8 were not strict replicates of those used in 1989/90. This limitation will not be relevant to future surveys and analyses of data, as formal sample plots have now been established.
The analysis underpinning this indicator was carried out by Chris Ellis, Royal Botanic Garden Edinburgh using data provided by Rothero et al (2008).
Suzanne Martin (RBGE) contributed as a co-author.