Vegetation succession on glacier forelands in the Jostedalsbreen region and Jotunheimen, south-central Norway

In this study four different aspects of primary successions on glacier forelands in South-Central Norway are investigated. First, general vegetation and environment trends, which have been observed by other scientists, were studied on two forelands. It is shown that the two selected forelands (one low- and one high-altitude foreland, Nigardsbreen and Storbreen, respectively) differ in the speed of vegetation cover change and in the overall species richness developed over the last 250 years since deglaciation. This is attributed to differences in the severity of the environment between the two forelands. Some support for an early peak in the number of species was found for the Nigardsbreen foreland, whereas the Storbreen foreland shows no significant trend in the development of species richness. Life-forms and soil-depth change on both forelands in the predicted manner. A novel approach for the use of Ellenberg indicator values for the estimation of pH-values from the existent vegetation shows highly significant correlations between predicted pH values and trends measured for similar terrain ages from a study by Messer (1988).
Investigation at two different scales indicated that small-scale disturbances (< 100 m) may influence the mosaic of the environment, which affects the results of the chronosequence approach. By using a strict geometrical sampling design more variable conditions entered the analyses than with the stratified random sampling schemes adopted by others, such as Matthews (1979b). Some loss in the power of analysing the data occurred, but the results are still consistent with hypotheses about primary succession on glacier forelands.
Second, new aspects of the temporal development and successional change of plant communities were investigated on the same two forelands. There is some evidence of succession from a pioneer community to the local climax community of the surrounding area for both forelands. There is also support for the correlation of timedependent environmental variables with the successional development of plant communities. A new application of Ellenberg indicator values in ordinations was assessed for its value in estimating average environmental conditions derived from the vegetation. As with the previous analyses, investigation of community development at two different scales supported the importance of sampling scale on the analysis of succession data.
Third, spatially explicit analyses of distribution patterns of dominant woody species was developed as a means to investigate processes and formulate hypotheses about primary succession on glacier forelands. The data for this part of the study was collected on five glacier forelands, three low-altitude (Nigardsbreen, Austerdalsbreen and Bødalsbreen) and two high-altitude (Storbreen and Høgvaglbreen). Pattern descriptors including perimeter/area index, autocorrelation measures and fractal dimensions, support the hypothesis of differential colonisation of wind and animaldispersed species. Even more convincing is the result that low- and high-altitude forelands show significant differences in the patterns exhibited by wind and animals dispersed species. This result is thought to be related to the differences in environmental severity affecting the establishment of colonising species.
Finally, logit modelling of the distributions of dominant woody species provides insights into the sampling effort needed to gather enough data for meaningful analyses. It also leads to the identification of important factors influencing the distribution of those species.

Advisor: J.A. Matthews, R