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Some notes on the microclimate associated with Thamnolia

vermicularis var. subuliformis from Snowdon, North Wales

A. PENTECOST and J. H. WILLIAMS

Pentecost, A. & Williams, J. H. 2002. Some notes on the microclimate

associated with Thamnolia vermicularis var. subuliformis from Snowdon,

North Wales. Graphis Scripta 13: 5963. Stockholm. ISSN 0901-7593.

During 1999 the estimated surface temperature of Thamnolia thalli ranged

from -7.7 to 24.5° C (3-day means). Precipitation occurred on 251 days (69

% of the year) and thalli were snow-covered for 90 days. The Snowdon

(Wales) population is small and declining, perhaps as a result of acid

precipitation which may be exacerbated by summer sheep grazing. Growth

rate was monitored over several years giving annual branch elongation rates

between 0.94 and 5.35 mm.

Allan Pentecost, Department of Life Sciences, King's College London,

Franklin-Wilkins Building, 150 Stamford Street, London SE1 9 NN.

J. H. Williams, School of Agricultural and Forest Sciences, University of

Wales, Bangor, Gwynedd LL57 2UW.

The lichen Thamnolia vermicularis var.

subuliformis is one of about 40 arctic-alpine

species which occur in North Wales

(Pentecost 1987). It is currently known from

three welsh mountains and was first recorded

from Cadair Idris by T. Salwey (1844). It was

first recorded from Snowdon by W. Watson in

August 1915 ’at 3,200 feet’ (BMNH).

Snowdon was visited regularly by

lichenologists in the 19th Century, so the late

recording is a little surprising, suggesting that

as now, it was not a common plant on the

mountain. It is likely to be close to the edge of

its range, as it becomes more frequent further

north on mountains of similar altitude and

does not occur on the mountains of South

Wales.

The species is currently restricted on

Snowdon to a few isolated patches on Crib-y-

Ddysgl (Nat grid. Ref. 23/60865508, alt. 1015

m) and the rocks above Clogwyn

(23/60085544, alt. 820 m). Since May 1972

when the senior author first observed it on

Snowdon, it appears to have undergone a

decline as it was fairly easy to find at that

time. In Britain the centre of distribution for

Thamnolia is in the Scottish Highlands where

it is widespread, even approaching sea level in

the north (Gilbert 2000). It also occurs on a

few mountains of the English Lake District.

The Cadair Idris site is currently its most

southerly location in Britain (Seaward &

Hitch 1982).

Little is known of the ecology of

Thamnolia vermicularis. It occurs as two

varieties, the var. vermicularis containing

thamnolic acid and the var. subuliformis with

baeomycesic and squamatic acids. Only the

latter is known from the British Isles but both

varieties are known from the adjacent

continent. The varieties are widespread in the

arctic-alpine heaths of Scandanavia where

they are found growing on soil or directly on

limestones (Sheard 1977; Santesson 1993).

Thamnolia is noteworthy among the

macrolichens in having no known sexual

stages, and lacking both soredia and isidia,

presumably reproducing largely by


60 Allan Pentecost & J. H. Williams GRAPHIS SCRIPTA 13 (2002)

fragmentation. Conidia have been described

by Ozenda & Clauzade (1970, p.759) from

France, but are not apparently reported from

the British Isles.

In this paper we have taken advantage of

the fact that Snowdon summit has a remotely

operating continuous weather station

providing extensive data on conditions at the

summit. The station is in close proximity to

the Thamnolia sites permitting a detailed

analysis of conditions over long periods of

time. The summit is also easy to access with

good paths providing year-round monitoring

of the site.

Methods

Small patches of Thamnolia were investigated

at the Crib-y-Ddysgyl site at altitudes of 975-

1015 m. Thalli were dispersed among lowgrowing

vegetation or grew directly on soil.

Monitoring began in August 1994 initially on

2 patches with a third added in 1999. Patches

were photographed in colour with a Nikon FT

camera from a set position on 6 occasions up

to April 2000. Close-up photographs were

taken from a fixed position with an adjacent

mm scale and measurements compared

manually. Digital methods were not used due

to the sparsity of cover and clarity of the

pictures obtained. At each site, thallus surfacetemperature

and air temperature was measured

with an Edale type D515 thermistor, the latter

at 1m height in shade. To obtain seasonal

surface temperature estimates a proxy method

was employed by regressing a set of 20 air

temperature measurements onto thallus

temperature. The resulting linear regression

equation (Thallus temp. = 1.51 Air temp. -

0.32) was found to be significant by ANOVA

(P


GRAPHIS SCRIPTA 13 (2002) Thamnolia vermicularis from Snowdon 61

Figure 1. Climatic data for the Snowdon Thamnolia sites during 1999: Surface temperature

estimates (3-day means) of thalli.

have been covered by snow for 90 days (25 %

of the year).

Significant precipitation, defined here as

>=1mm rain per day, fell on 190 days with

less than 1mm on a further 61 days (Figure 2).

Total precipitation for 1999 at Snowdon

summit was 2636 mm. The longest period

without recorded rainfall was 8 days (24-31

July) but there was an instrument breakdown

during August (Figure 2) where only monthly

data were available. Thamnolia was wetted by

precipitation for at least 251 days (69 % of the

year). Kershaw (1975) found a surface

temperature difference of up to 7°C between

wet and dry thalli of Thamnolia, dry thalli

being subjected to higher temperatures. Most

of the surface measurements conducted on

Snowdon were on wet thalli, but where dry

thalli were measured such large differences

were not observed. This was probably due to

exposure to the prevailing westerly winds.

There are few data with which to compare

the growth of Thamnolia, but Lange et al.

(1995) found that under high light intensities,

the temperature for optimal net photosynthesis

was 13-22°C, which coincides with summer

surface values on Snowdon. This suggests that

Thamnolia growth occurs mainly in the

summer. The decline of Thamnolia on

Snowdon is cause for concern. Acid

precipitation from vehicle emissions and

power stations may be responsible since

Wales as a whole is affected by this form of

pollution (Edwards et al. 1990) and the soils

upon which the species grow are acidic and

probably poorly buffered.

The colonies growing on Cadair Idris

appear to be thriving, occurring in

considerable areas (J. Grasse, pers. comm.).

Deposition rates of sulphur- and nitrogenbased

acidity were estimated between 1984

and 1995. The 20 km × 20 km Snowdon

square showed markedly higher rates of wet,


62 Allan Pentecost & J. H. Williams GRAPHIS SCRIPTA 13 (2002)

Figure 2. Climatic data for the Snowdon Thamnolia sites during 1999 Precipitation (3-day

totals) at the Snowdon summit weather station.

dry and total acid deposition than did the 20

km × 20 km Cadair Idris square (Stevens et al.

1997). Another possible explanation is grazing

pressure. During summer, sheep graze the low

turf of Crib y Ddysgl and are bound to disrupt

thalli by trampling. There was clear evidence

of grazing adjacent to the sites so some

damage appears inevitable, but it is not clear

whether the intensity of grazing has varied

historically, or how trampling affects reestablishment

of the lichen fragments. Cooper

et al. (2001) noted damage to High Arctic

lichens and its amelioration by sustained

periods of precipitation. However at our

Snowdon sites there was no evidence of

regeneration of damaged thalli and the

population as a whole appears to be declining

rapidly. Another possible cause of these

changes is the global increase in temperature

over the past 30 years. Since Cadair Idris and

Snowdon receive almost identical weather, but

only Snowdon has suffered a decline in

Thamnolia, such changes are unlikely to be

the cause of decline.

Acknowledgements

We thank Dr. M. O. Hill for some of the

bryophyte identifications and Jack Grasse for

information on the distribution of Thamnolia

on Cadair Idris. The senior author is grateful

for a small travel grant from the British

Lichen Society.

References

Barry, R. G. 1981: Mountain weather and

Climate. Methuen, London and New

York.


GRAPHIS SCRIPTA 13 (2002) Thamnolia vermicularis from Snowdon 63

Cooper, E. J., Smith, F. M. & Wookey, P. A.

2001: Increased rainfall ameliorates the

negative effects of trampling on the

growth of High Arctic forage lichens.

Symbiosis 31:153-171.

Edwards, R. W., Gee, A. S. & Stoner, J. H.

1990: Acid waters in Wales. Kluwer,

Dordrecht.

Gilbert, O. L. 2000: Lichens. New Naturalist

Series No. 86. Harper Collins, London.

Kershaw, K. A. 1975: Studies on lichendominated

systems XII. The ecological

significance of thallus colour. Can. J. Bot.

53: 660-667.

Lange, O. L., Hahn, S. C., Müller, G., Meyer,

A. & Tenhunen, J. D. 1996: Upland tundra

in the foothills of the Brooks Range,

Alaska : Influence of light, water content

and temperature on CO2 exchange of

characteristic lichen species. Flora 191:

67-83.

Ozenda, P. & Clauzade, G. 1970: Les Lichens:

flore biologique et flore illustrée. Paris,

Masson et Cie.

Pentecost, A. 1987: The lichen flora of

Gwynedd. Lichenologist 19: 97-166.

Salwey, T. 1844: A list of lichens gathered in

different parts of Wales, principally in the

neighbourhood of Barmouth, with a few

casual observations upon some of the

species. Ann. Mag. Nat. Hist. 13: 25-32.

Santesson, R. 1993: The lichen and

lichenicolous fungi of Sweden and

Norway. SBT-förlaget, Lund.

Seaward, M. R. D. & Hitch, C. J. B. 1982:

Atlas of the lichens of the British Isles.

Vol. 1. C. Natural Environment Research

Council, Institute of Terrestrial Ecology,

Cambridge.

Sheard, J. W. 1977: Paleogeography,

chemistry and taxonomy of the lichenized

ascomycetes Dimeleana and Thamnolia.

Bryologist 80: 100-118.

Snowdon Weather Station. www.fhc.co.uk/

weather

Stevens, P. A., Ormerod, S. J. & Reynolds, B.

1997: Final Report on the Acid Waters for

Wales. Vol. 1. Main text. Institute of

Terrestrial Ecology, Bangor, Wales, U.K.

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