Biatora aegrefaciens – återfunnen efter 119 år

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.