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

SCCAP objectives:
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

Latest figures

Snow-bed specialist bryophytes

All bryophytes

Western Scotland

10% decline

18% decline

Eastern Scotland

4% increase

18% increase

Trend
At a glance
  • 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.

Related indicator:

NB16b Abundance/frequency of specialist and generalist species: butterflies

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.

Region

Site Code

Site Name

Western

S1

Beinn Dearg

S2

Ben Wyvis, North Coire

S3

Mam Sodhail, Lochan Uaine

S4

White Mounth, Coire Boidheach

S5

White Mounth, Glas Allt

S6

Creag Meagaidh, West Coire

S7

Ben Lawers, An stuc

S8

Ben Lawers, NE Face

Eastern

S9

Cairngorm, Ciste Mhearad

S10

Carn Lochan, Coire Domhain

S11

Carn Lochan, Coire Domhain

S12

Ben Macdui, Lower Garbh Uisge Beag

S13

Ben Macdui, Upper Garbh Uisge Beag

S14

Ben Macdui, North Slope

S15

Ben Macdui, Upper Garbh Uisge Mor

S16

Ben Macdui, Bealach 1232m

S17

Braeriach, Garbh Coire Mor

S18

Braeriach, Garbh Coire Mor E Gully

S19

Beinn a Bhuird, Coire an t’Snaechda

S20

Beinn a Bhuird, Dubh Lochan

S21

Beinn a Bhuird, North Top

S22

Beinn a Bhuird, Garbh Coire

Table 1Names 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 starkeiPolytrichum 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.