Comparative vegetation analyses of two transects crossing a characteristic glacier valley in the Central Alps
Raffl, Corinna; Erschbamer, Brigitta
Numerous ecological studies have concentrated on primary plant succession within glacier forelands. However, hardly any investigations addressed the vegetation of the immediate surrounding and its possible influence on the primary colonization processes of the glacier forelands. This study had three principal aims: (i) to identify and describe the sequence of vegetation pattern along two transects crossing the glacier valley Rotmoostal (Ötztal, Austria); (ii) to compare the yielded pattern on the glacier foreland with that on the adjacent slopes; (iii) to assess the influence of the slope vegetation on the primary succession of the glacier foreland. Vegetation and environmental data were collected along two transects across morainic ridges formed by intermittent glacial retreats in 1858 and 1923. Six plant communities were identified, comprising pioneer community, community of early successional species, initial grasslands, Caricetum curvulae, Caricetum sempervirentis and Caricetum frigidae. The first three assemblages were dispersed over the glacier foreland. The Carex-grasslands occurred mainly on the valley slopes. Site age and a combination of environmental factors were recognized as the determining factors on the vegetation patterns. Comparing the vegetation sequence across transects, the development with time from a mosaic pattern towards a more homogeneous structure can be observed. Vegetation cover increased during primary succession. Significant differences in species richness between glacier foreland and the adjacent slopes were recorded only along the older transect. Late successional species, which are characteristic for the valley slopes, were already established on some plots of the 1923 moraine. On the oldest side moraine (1858) the progress of succession proceeded already to the climax stage: alpine grasslands such as Caricetum curvulae and Caricetum sempervirentis were recorded in several plots. However, on the ground moraines succession certainly needs several hundred years to result in the climax stage of alpine grasslands.