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 Hylocomium splendens, using retrospective analyses of growth. We hypothesized that relationships between growth and climate would be simpler in an ectohydric moss than in higher plants and that the moss could provide high signal-to-noise ratios of responses to climatic variation. 2. Growth parameters of the moss were strongly correlated with early summer temperatures and with the length of the growing season. Annual segment mass, growth rates and degeneration rates were highest at the mildest 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 sites were significantly correlated with June and July temperatures and to a lesser extent, with early-season precipitation at one of the sites. 4. The moss currently tolerates a wide range of climates and large interannual variations in temperature and is likely to be at risk from climatic change only at the southern edge of its range. 5. The climate-change component most likely to affect the growth of H. splendens in the Arctic and Subarctic will be a lengthening of the growing season and in increase in early summer temperatures provided that moisture is not limiting. 6. Hylocomium splendens is a suitable species for monitoring climatic change at a circumarctic scale.