The Vegetation of the Storbreen Gletschervorfeld, Jotunheimen, Norway. III. Vegetation-Environment Relationships

The Storbreen glacier foreland has been the sub- ject of a spatial approach to vegetation chronosequence studies (Papers I and II of the series), providing a detailed base-line for further study. It is argued here that an under- standing of primary succession requires knowledge of the relationships among and between environmental variables and plant communities. This paper reports an attempt to quantify such relationships for an altitudinally-restricted sub-set of 108 of the 638 permanent vegetation sites located on this glacier foreland. Twelve environmental variables and four vegetational (ordination) axes are examined individually and collec- tively using non-parametric correlation and 2-D and 3-D graphical displays. Significant roles are suggested for ter- rain age, acting through disturbance regime (especially by small-scale frost action) and soil development, and for microtopography involving site moisture regime, length of snow-lie and microclimate. The explanation of vegetation structure is improved by viewing environmental variables as forming 'factor com- plexes', defined by a plexus approach. This involves in-series application of Detrended Correspondence Analysis (DCA) and Non-metric multidimensional scaling (NMDS). The results of these indirect gradient analyses are compared with those from direct gradient analysis by Canonical Correspondence Analysis (CCA), providing further support for the existence of terrain age and microtopographic factor complexes. Although there are complex spatial inter-relationships among the variables discussed, the strength of the relationship between the first ordination axis and terrain age lends credence to the application of a multivariate form of the chronosequence approach to succession on this foreland.