Download snow-bed species

Methodology Statement
Generalist species more able to cope than specialist species:
snow-bed species
Indicator
Frequency of specialist and generalist species in snow-bed communities
Indicator type:
Risk/opportunity
Impact
Action
X
SCCAP Theme
SCCAP Objective
CCRA risk/opportunity
Natural Environment
N2: Support a healthy and
diverse natural environment
with capacity to adapt.
Generalist species more
able to adapt than
specialists
Author(s)
Chris Ellis, Royal Botanic Garden Edinburgh.
Acknowledgements
Dave Genney, SNH.
Why are snow-bed species of interest?
A British vegetation type which is strongly associated with areas of late-lying snow occurs in
the Scottish mountains, and is described in the UK’s National Vegetation Classification [1] as
comprising three community-types: (a) U8, Carex bigelowii-Polytrichum alpinum sedgeheath; (b) U11, Polytrichum sexangulare-Kiaeria starkei snow-bed; (c) U12 Salix herbaceaRacomitrium heterostichum snow-bed.
These three communities are priority features for conservation; they are sub-types nested
within the broad Annex I habitat ‘Siliceous alpine and boreal grasslands - 6150’ [2], and form
an important constituent within protected sites such as the Cairngorms Special Area of
Conservation [3].
The snow-bed vegetation is characterised by mosses and liverworts (bryophytes) which are
‘snow-bed specialists’ and might be considered as indicator species for the habitat [4]. The
snow-bed bryophyte community includes BAP/priority species such as Andreaea nivalis and
Marsupella arctica, and the Schedule 8 species Gymnotrium apiculatum.
Information on the status of snow-bed bryophytes would provide a valuable assessment of
the condition of snow-bed vegetation, while also being representative of wider challenges in
biodiversity and climate change:
(1) Snow-bed species are niche specialists, and monitoring their status is especially relevant
during a period when observational data indicates an increasing homogenisation of the
mountain flora, through an expansion of generalists [5,6];
(2) Conceptually, snow-bed species occur at a latitudinal and altitudinal ‘range edge’ in
Scotland, capturing a scenario in which species are unable to track climate change through
migration along a continuous environmental gradient via inter-connected habitat.
(3) Areas of late-lying snow provide ecosystem services in addition to their unique
biodiversity, for example by sustaining the baseflow of streams and rivers following the
main period of snowmelt [7].
References
[1]
Averis, A., Averis, B., Birks, J., Horsfield, D., Thompson, D. & Yeo, M. (2004) An Illustrated
Guide to British Upland Vegetation. Joint Nature Conservation Committee, Peterborough.
[2]
JNCC Habitat Account – 6150, Siliceous alpine and boreal grasslands.
http://jncc.defra.gov.uk/protectedsites/sacselection/habitat.asp?FeatureIntCode=H6150
(accessed 14th June 2013)
[3]
JNCC Cairngorms SAC Account.
http://jncc.defra.gov.uk/protectedsites/sacselection/sac.asp?EUCode=UK0016412
(accessed 14th June 2013)
[4]
Woolgrove, C.E. &Woodin, S.J. (1994) Relationships between the duration of snowlie and
the distribution of bryophyte communities within snowbeds in Scotland. Journal of
Bryology, 18: 253-260.
[5]
Britton, A.J., Beale, C.M., Towers, W. &Hewison, R.L. (2009) Biodiversity gains and losses:
evidence for homogenisation of Scottish alpine vegetation. Biological Conservation, 142,
1728-1739.
[6]
Ross, L.C., Woodin, S.J., Hester, A.J., Thompsom, D.B.A. & Birks, H.J.B. (2012) Biotic
homogenization of upland vegetation: patterns and drivers at mutiple scales over five
decades. Journal of Vegetation Science, 23, 755-770.
[7]
Dunn, S.M., Langan, S.J., Colohan, R.J.E. (2001) The impact of variable snow pack
accumulation on a major Scottish water resource. The Science of the Total Environment,
265: 181-194.
What are the key climate hazard(s) affecting snow-bed species?
Snow-bed vegetation and associated specialist species may be dependent on late-laying
snow for a variety of reasons [1], for example: (a) intolerance of extreme low temperatures,
(b) a demand for soil moisture throughout the growing season, (c) specific adaptation for
physiological activity during an ephemeral period of snowmelt and an associated nutrient
pulse, or (d) reduced competition from co-occurring species which require a longer growing
season.
The link between the number of late-lying snow-beds (e.g. beyond July [2]) and their size,
and the climate, are broadly established, being dependent on winter and spring
temperatures, and factors of wind and topography affecting drift [2]. Alongside warming
temperatures, UKCP09 scenarios project a decline in mean snowfall rate of 65-80 % over
montane areas generally by the 2080s [3], with regional assessments also strongly suggesting
a reduction in snow cover across altitudinal bands in Scotland [4].These climate projections
underpin bioclimatic models which indicate a loss of suitable niche space for specialist
snow-bed species and a transition to generalists [5].
It is expected that a long-term trend towards a reduction in the spatial extent (snow-bed
size) and length of snow-lie (snow-bed duration) will shift snow-bed vegetation
composition, with conservation-priority snow-bed communities transitioning towards a
widespread community-type typical of more open montane conditions. Nevertheless, given
the potential variety of ecological factors controlling each species’ association with and
distribution within snow-beds [1,6], the signature of change away from a snow-bed
community may not be as simple as a linear decline across all snow-bed associated species.
References
[1]
Björk, R.G. &Molau, U. (2007) Ecology of alpine snowbeds and the impact of global
change. Arctic, Antarctic and Alpine Research, 39: 34-43.
[2]
Watson, A., Davison, R.W. & French, D.D. (1994) Summer snow patches and climate in
northeast Scotland, U.K. Arctic and Alpine Research, 26: 141-151.
[3]
Jenkins, G., Murphy, J.M., Sexton, D.M.H., Lowe, J.A., Jones, P. &Kilsby, C. (2010) UK
Climate Projections: Briefing Report. Met Office.
[4]
Trivedi, M.R., Browne, M.K., Berry, P.M., Dawson, T.P. &Morecroft, M. D. (2007) Projecting
climate change impacts on mountain snow cover in Central Scotland from historical
patterns. Arctic, Antarctic and Alpine Research, 39: 488-499.
[5]
Trivedi, M.R., Morecroft, M.D., Berry, P.M. & Dawson, T.P. (2008) Potential effects of
climate change on plant communities in three montane nature reserves in Scotland, UK.
Biological Conservation, 141: 1665-1675.
[6]
Woolgrove, C.E. &Woodin, S.J. (1994) Relationships between the duration of snowlie and
the distribution of bryophyte communities within snowbeds in Scotland. Journal of
Bryology, 18: 253-260.
What is the exposure of snow-bed species to climate change?
A comprehensive survey of snow-bed vegetation was carried out in 1989-1990, for 58 areas
of late-lying snow across Scotland [1]. The area of Scotland’s snow-bed vegetation is
expected to total c. 160-250 ha across these and other isolated patches. Scottish Natural
Heritage commissioned a repeat survey of the original 58 snow-beds during 2007-2008, and
22 were successfully resurveyed (Fig. 1, Table 1); these were located across western and
central mountain ranges, and within the eastern and relatively more continental Cairngorm
Mountains [2,3].
A report to SNH compared the composition of bryophyte communities, and the frequency of
species, between the two survey periods [2,3]. The results demonstrated only very tentative
evidence for change in snow-bed communities [2] and a shift in the frequency of certain
species. Notably, this included a statistically significant 13% decline in the frequency of the
snow-bed specialist liverwort Moerckia blytii [3]. However, trends in frequency shifts 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 %) [3]. This lack of a
clear trend may demonstrate individualistic species responses consistent with a
reorganisation of snow-bed vegetation structure, or may reflect the fact that the repeat
sampled plots were not strictly replicates, but were resampled for equivalent vegetationtypes across the time-periods. For the purpose of future monitoring, permanent plots have
been established.
For the purposes of this indicator, the focus was less on species composition, and instead on
broad measures of vegetation structure: vascular plants, with grasses as a specific example
guild, and bryophytes generally, with NVC snow-bed species as indicators. Accumulated
cover values within these groups were analysed separately for western/central and eastern
snow-beds (Fig. 1) for those plots within which a NVC dominant snow-bed bryophyte had
been recorded in 1989-1990:
(a) Polytrichum alpinum
(b) Polytrichum sexangulare
(c) Kiaeria starkei
(d) Racomitrium heterostichum
This takes into account possible decadal-scale differences in the rate, magnitude and intraannual direction of climate change between these regions [4].
Analysis demonstrated a decline in the frequency of snow-bed NVC indicators and
bryophytes generally, for the western snow-beds, implying structural change in the
vegetation (Fig. 2). In contrast, cover values for bryophytes increased across the Cairngorm
snow-beds (Fig. 2). There is preliminary evidence for structural change in the snow-bed
vegetation, which may show regional variation.
When available Snow Survey of Great Britain data will be provided in this section.
References
[1]
Rothero, G.P. (1991) Bryophyte-dominated snow-beds in the Scottish Highlands.
Unpublished MSc thesis, University of Glasgow.
[2]
Rothero, G.P., Grytnes, J.-A., Birks, H.J.B. & Genney, D. (2008) Effects of climate change on
bryophyte-dominated snowbed vegetation. Scottish Natural Heritage 104 pp.
[3]
Rothero, G., Birks, J., Genney, D., Grytnes, J.-A. & Long, D. (2011) Climate change and its
consequences on bryophyte-dominated snowbed vegetation. The Changing Nature of
Scotland (ed. by S.J. Marrs, S. Foster, C. Hendrie, E.C. Mackey and D.B.A. Thompsom), pp.
435-440. TSO Scotland, Edinburgh.
[4]
Jenkins, G., Murphy, J.M., Sexton, D.M.H., Lowe, J.A., Jones, P. &Kilsby, C. (2010) UK
Climate Projections: Briefing Report. Met Office.
What are the key factors affecting the vulnerability of snow-bed species to climate
change?
There is direct vulnerability of snow-bed associated species if climate change causes a
decline in montane snow cover with impacts extending to areas of late-lying snow. There
are various sources of information addressing temporal variability in the extent of snowcover in the Scottish mountains [1]. These data have been collected for a variety of purposes,
and would require careful meta-analysis to provide a synthesis. Recently, Met Office snow
survey data for a period 1945-2007 has been digitised [1], and will become publically
available on request [2], with recommendations for improving the quality of snow survey
information into the future [1].
In addition to direct impacts on late-lying snow, a range of additional existing pressures can
be identified:
1. Air pollutants can accumulate at high levels in the late-lying snow-pack, leading to
physiological damage for sensitive snow-bed bryophytes [3,4];
2. Human activity can result in localised pollution impacts through waste [5], or
trampling of the sensitive vegetation.
References
[1]
Spencer, M. (2012) Scottish snowline observations – the past and the future. BHS 11th
National Symposium, Dundee.
http://www.hydrology.org.uk/assets/2012%20papers/Spencer_49.pdf (accessed 17th June
2013)
[2]
Met Office Integrated Data Archive System (MIDAS) Land and Marine Surface Stations
Data (1853-current).
http://badc.nerc.ac.uk/view/badc.nerc.ac.uk__ATOM__dataent_ukmo-midas
(accessed 17th June 2013)
[3]
Woolgrove, C.E. &Woodin, S.J. (1996) Effects of pollutants in snowmelt on Kiaeriastarkei, a
characteristic species of late snowbed bryophyte dominated vegetation. New Phytologist,
133: 519-529.
[4]
Woolgrove, C.E. &Woodin, S.J. (1996) Ecophysiology of a snow-bed bryophyte
Kiaeriastarkei during snowmelt and uptake of nitrate from meltwater. Canadian Journal of
Botany, 74: 1095-1103.
[5]
Cairngorm Mountain Ranger Service – ‘Keep Cairngorm Snow White’.
http://www.cairngormmountain.org/sites/default/files/Snow%20White%20Project_0.pdf
(accessed 14th June 2013) as reported on the BBC:
http://news.bbc.co.uk/1/hi/scotland/highlands_and_islands/7170227.stm
(accessed 14th June 2013).
Are there any current or planned adaptation actions to address the climate change risk to
snow-bed species?
Currently adaptation to address climate change risk is focussed on policy objectives. For
example, bryophyte assemblages are a notified feature of the Eastern Cairngorms SSSI, and
a component of this feature (snow-bed bryophytes) were considered to be in unfavourable
condition during the last round of Site Condition Monitoring (SCM), possibly as a direct
consequence of climate change. The condition of snow-bed bryophytes will be assessed
over several cycles of SCM, and if further decline in condition is confirmed as a consequence
of external pressures (climate change) it could trigger removal from the SSSI citation. This is
an example of a policy adaptation consistent with managed retreat.
Alternative adaptation options include the reduction of other environmental pressures (e.g.
reducing direct human impacts through the reduction of waste, see above), through to
experimental infrastructure projects, including: (a) snow-fences to encourage drifting and
retain late-lying snow, as demonstrated in an experimental framework[1,2], (b) textile
blankets as used in the Alps to prevent glacier melt[3], or (c) artificial snow blowing to
augment natural deposits. Currently, none of these options are under consideration as a
formal approach to conservation.
References
[1]
Scott, P.A. & Rouse, W.R. (1995) Impacts of increased winter snow cover on upland
tundra vegetation: a case example. Climate Research, 5: 25-30.
[2]
Wipf, S. &Rixen, C. (2010) A review of snow manipulation experiments in Arctic and alpine
tundra ecosystems. Polar Research, 29: 95-109.
[3]
‘Researchers cover up melting glaciers’ – as reported in USA Today:
http://usatoday30.usatoday.com/weather/climate/2005-07-17-glacier-blankets_x.htm
(accessed 14th June 2013).
Supporting graphics
Fig. 1: The location of 22 repeat-survey snow-beds for which data was made available by
Scottish Natural Heritage. Snow-beds were grouped into two regions for analysis here:
Region 1 (red box), with snow-beds 1.-8., representing more western and central mountain
ranges, and Region 2 (blue circle), with snow-beds 9.-22., representing the eastern and
relatively more continental Cairngorm snow-beds (cf. Table 1).
Table 1. Location data for 22 snow-bed survey sites (cf. Fig. 1) for which vegetation data was
made available by Scottish Natural Heritage.
Region
Site
Code
SNH
Reference
Site Name
Location
# plots
S1.
S2.
S3.
S4.
S5.
S6.
S7.
S8.
33
30
34
44
45
54
57
58
Beinn Dearg
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
NH256815
NH466686
NH120255
NN233845
NN241846
NN408871
NN637433
NN636413
4
4
1
5
3
1
2
1
S9.
S10.
S11.
S12.
S13.
S14.
S15.
S16.
S17.
S18.
S19.
S20.
S21.
S22.
1
3
19
4
5
6
17
18
13
14
7
8
9
10
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
NJ011045
NH992023
NH986100
NH994008
NH999004
NH990001
NN994992
NN999989
NN940980
NN942983
NO094979
NO091991
NJ095009
NJ104016
18
11
9
10
6
4
10
1
4
2
5
3
7
4
Western
Eastern
Fig. 2: Time-series comparison (1989/90-2007/8) 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. Statistical values are for a comparison
between sets of paired plots within each of the two contrasting regions (western and
eastern), using a Wilcoxon paired sample test.
Eastern Snow-beds
(sites 9.-22., n = 83 plots)
Western Snow-beds
(sites 1.-8., n = 20 plots)
80
60
40
20
0
-20
-40
V = 173,
P = 0.008
N
VC
s
ry
op
hy
te
s
Al
lb
hy
te
ts
br
yo
p
pl
an
ed
sn
ow
-b
Va
sc
ul
ar
ra
ss
es
V = 367, V = 1386, V = 1357, V = 584,
P = 0.97 P = 0.99 P = 0.154 P < 0.001
G
s
ry
op
hy
te
s
hy
te
Al
lb
br
yo
p
pl
an
ed
sn
ow
-b
Va
sc
ul
ar
ra
ss
es
-80
ts
V = 37.5, V = 77, V = 142,
P = 0.6 P = 0.99 P = 0.061
N
VC
-60
G
Change in percent cover (1989/90 - 2007)
100