BETWEEN-YEAR VARIATION IN CLIMATE-RELATED GROWTH OF CIRCUMARCTIC POPULATIONS OF THE MOSS HYLOCOMIUM SPLENDENS

1. The correlation between climatic variables and past (up to 20 years ) growth was studied in seven circumarctic populations of the moss Hyl ocomium splendens, using retrospective analyses of growth. We hypothes ized that relationships between growth and climate would be simpler in an ectohydric moss than in higher plants and that the moss could prov ide high signal-to-noise ratios of responses to climatic variation. 2. Growth parameters of the moss were strongly correlated with early sum mer temperatures and with the length of the growing season. Annual seg ment mass, growth rates and degeneration rates were highest at the mil dest subarctic sites and lowest at the high arctic site. In contrast, 'longevity' (age of the oldest segment) increased at the climatically harsher sites. 3. Between-year growth variations at two contrasting si tes were significantly correlated with June and July temperatures and, to a lesser extent, with early-season precipitation at one of the sit es. 4. The moss currently tolerates a wide range of climates and large interannual variations in temperature and is likely to be at risk fro m climatic change only at the southern edge of its range. 5. The clima te-change component most likely to affect the growth of H. splendens i n the Arctic and Subarctic will be a lengthening of the growing season and in increase in early summer temperatures provided that moisture i s not limiting. 6. Hylocomium splendens is a suitable species for moni toring climatic change at a circumarctic scale.