Pioneer vegetation on glacier forelands in southern Norway: emerging communities?

摘要

Question: How variable is the pioneer plant community on glacier forelands in southern Norway, both in terms of species composition and geographical distribution? Location: The Jotunheim and Jostedalsbreen regions of southern Norway (61 degrees -62 degrees N, 6 degrees -9 degrees E). Methods: The relative frequencies of vascular plant species were recorded in the pioneer zones of 43 glacier forelands, with an altitudinal range of 80-1860 m (boreal to high alpine) and an east-west range of 100 km. Classification and ordination techniques were used to search for evidence of consistently recurring communities, variability along a continuum or stochasticity. Results: Mean variability in species composition between all glacier forelands sampled was 65% (Sorensen dissimilarity). Poa alpina, Oxyria digyna, Deschampsia alpina and Festuca ovina had the highest frequency, occurring on over 80% of forelands. Non-metric multidimensional scaling did not reveal clear divisions between groups of sites, but cluster analysis, multi-response permutation procedures and indicator species analysis suggested two sub-communities: the Saxifraga cespitosa-Trisetum spicatum sub-community is restricted to forelands above 1100 m in the Jotunheim region; whereas the D. alpina-O. digyna sub-community has a wider altitudinal range of 80-1780 m. Variance partitioning indicated that altitude alone accounts for 24%, distance east for 18%, and the component shared by altitude and distance east for 17% of the variance in species composition. Conclusions: At the broadest scale, pioneer vegetation on the glacier forelands can be viewed as a single P. alpina-O. digyna community of predominantly wind- and water-dispersed perennials. However, this community shows a high degree of variability, with dominant species missing from a number of sites, and is poorly structured, suggesting a degree of stochasticity. Furthermore, the pioneer vegetation can be dissected within a continuum of variation to produce two emerging sub-communities, reflecting the influence of environmental factors and, possibly, early successional development within the pioneer zone. Variance partitioning indicates that altitudinal and continentality gradients are important in accounting for a significant proportion of the variability within this dataset.