23_237-252.pdf

238 THE LICHENOLOGIST Vol. 23
FIG. 1. Vegetation on a tree-covered spur of a mountain with a north-east facing slope (left part) and
a south-west facing slope (right part). Distribution of cluster-groups.
The vegetation was studied by cluster analysis and by principal component
analysis (PCA). Good correlations between the vegetation and the distribution
of abiotic factors such as light and pH were observed.
A cluster analysis of the complete research area showed several groupings
(Fig. 1, A-F) each representing homogeneous vegetation according to the rules
of plant sociology. The principal species in each group, higher plants as well as
lichens and mosses, and their abundance are given in Fig. 2. No lichens were
present (epiphytic lichens were excluded) in the cluster groups A and B from
the north-east facing slope. In group C the first species of Cladonia appear, but
only C.furcata is found with large numbers of thalli. The main occurrence of
Cladonia is in the cluster groups E and F, with a marked increase in Parmelia
conspersa and Polytrichum piliferum in cluster group F. This means that on the
southern-facing slope lichens and mosses could be used together with the
higher plants for the definition of the cluster groups.
A PCA of both slopes together included the cryptogams and resulted in a
clear picture. Only the occurrence of the plants and not their abundance was
used. The resulting scatter showed a gradient that could be separated into 10
parts (Fig. 3). The gradient shows a continuous change starting from the lower
part of the northern slope, passing upwards to the transition zone between the
two slopes and ending in three open areas at the margin of the south slope. A
comparison between PCA and cluster analysis shows a high degree of conformity.
The distribution of abiotic factors was also investigated by PCA and a
high degree of conformity between the distribution of vegetation and the light
intensity (Fig. 4), the pH and the ground cover by dead leaves was found.