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240 THE LICHENOLOGIST Vol. <strong>23</strong> 4 * 4 5 1 33 '• X # . -a 1 2 ,»< ' FIG. 3. PCA of the occurrence of phanerogams and cryptogams on the mountain spur. The gradient is divided into 10 parts and starts from the lower part of the northern slope and ends at the upper margin of the south slope. A separate PCA was made for the south-west exposed slope, which alone is of interest for the cryptogams. Not only the distribution of clusters along the first axis, but also the arrangement of individual species showed the same interesting pattern. For example, Polypodium vulgare was found at one end of the axis and Calluna vulgaris at the opposite end. Festuca cinerea occurs mainly in the middle part of the axis. This corresponds with a light gradient from dark {Polypodium) to light {Calluna). Of the cryptogams Polytrichum piliferum is found at the end of the axis together with Calluna. For Cladonia a characteristic distribution exists along the axis: all species occur in the middle part of the axis and not at the extremes but C.furcata and C. squamosa are found nearer to the darker part of the gradient and C. arbuscula and C. rangiferina in the lighter areas. This summary of the experiments shows that cryptogams can be included with phanerogams in both cluster analysis and PCA, and that they contribute to the study of the whole phytocoenosis. To summarize the results: Cladonia (sect. Cladina) species are absent in the shady beech forest and in the open sunny areas of the oak forest but dominate the rest of the oak forest. The open oak forest contains an undergrowth of certain cryptogams, which can be included in the sociological characteristics of the Quercetalia roboris-petraeae. This statement does not answer the question whether, for lichens and mosses, the open forest is a homogeneous area or an accumulation of completely different microhabitats. Probably only the sum of these habitats together gives
1991 Microclimate influences on lichens—Canters et al. 241 -ss- -50 SO too 180 X »0" a FIG. 4. PCA of the light intensity (largest dots = highest intensity). The gradient shows the same pattern as the PCA of the vegetation (see Fig. 3). the impression of homogeneity. In this case the separated associations of cryptogams are obscured by their inclusion into the description of the forest community. To answer this question the scale of research must be reduced. Lichen distribution in microhabitats in the forest The tree-crowns of the open forest are responsible for variations in the light intensity at ground level. Small 2 x 2 m plots were marked out at the border of shadow areas in such a way that in summer there was a gradient from light, warm and dry conditions at the lower left corner to dark, humid and cold conditions at the upper right corner. The result should be a gradient of those microclimatic factors that are most important to cryptogams. In winter, when the trees are bare, the microclimate is more homogeneous. Therefore the differentiation in the distribution of species must occur in the other months of the year. The spatial distribution of microclimatic data was recorded for every hour of the day; an example is given in Fig. 5. The microclimatic measurements were combined in a gradient, which is shown in Fig. 6 for three plots. The distribution of the plants was recorded in each quadrat including some higher plants and the dominant lichens and mosses. For mapping, the 2 x 2 m plots were divided into 400 small 10x10 cm quadrats. Figures 7 & 8 show the distribution in two plots. The upper row contains the frequently occurring plants common to all plots. The second row shows the distribution of frequently occurring plants found only in one or two quadrats. The last row
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