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248 THE LICHENOLOGIST Vol.<strong>23</strong> FIG. 12. Distribution pattern of species groups in an open area 1, Polytrichum formosum-Cladonia (Sect. Cladina) zone; 2, P. piliferum zone; 3, C. portentosa zone; 4, C. portentosa-Baeomyces transition zone; 5, Baeomyces zone; 6, Grimmia pulvinata zone; 7, other transition zones. lichens can only be explained by factors that are irrelevant to higher plants or at least different in their way of influencing the higher and lower vegetation. The influence of many factors such as light, water relations and insolation have been discussed in many papers. Some of these factors have already been mentioned together with the examination of the forest area (see above). Here, only some aspects will be reported that are often omitted. The influence of dead leaves The examination of small areas in the forest showed an influence of light and temperature on the distribution of cryptogams. The occurrence of many lichens showed a correlation with these factors and the real distribution patterns of these species could only be explained by work on this microscale. However, some species such as C.furcata seemed to be indifferent to light and temperature. The climatic conditions on the lichen-free, north-east facing slope should also be suitable for the species, but it does not occur there. This could be due to the influence of dead leaves, which gather on this slope in a thick layer. To test this hypothesis some transplantation experiments were carried out. Thalli of several species of Cladonia were transplanted from the south slope to the north slope. Each species was exposed on two 1 m 2 plots. One plot was regularly cleared of all dead leaves (plot B) while from the other only sufficient leaves were removed to prevent the lichens from being completely covered (plot A). The condition of the lichens and their disintegration was classified with a simple system. The development of the transplants is shown in Table 1.
1991 Microclimate influences on lichens—Canters etal. 249 TABLE 1. Condition of several transplanted Cladonia species Date 16 September 1976 6 October 1976 22 November 1976 17 February 1977 31 March 1977 13 May 1977 6 July 1977 8 September 1977 13 December 1977 1 March 1978 C. rangiferina A* B _ + — — - — — - 0 0 C. arbuscula A B + + — + — — + - + — + +-_0 + — __ 0 0 0 C. squamosa A B + + — - — - 0 0 0 0 + + + + — - --0 0 C.furcata A B + + + + + + + + + + + + + + + + + + + + + ++§ •Plot A with only a few leaves removed. Plot B regularly cleared of all dead leaves. X + +, Very good (thallus upright without any disintegration); +, good (some small discoloured parts); +, intermediate (discoloured parts and some spots with disintegration beginning; —, bad (thallus partly dead and disappearing, some parts still left alive); , very bad (only some parts of the thallus left, discoloured, broken down); 0, disappeared. §Fertile thallus with apothecia. The transplant experiment showed that for three of the four species the microclimate of the north slope is unsuitable and the thalli degenerate. The remaining dead leaves in plot A have an additional negative influence. On the other hand C. furcata can, as expected, survive under these microclimatic conditions only if the dead leaves are removed. In the completely leaf-free plot B even apothecia were formed. Dead leaves are therefore an extremely important factor for lichens in forest communities. On the south slopes most leaves are blown away by the wind. The remaining leaves do not lie on the cushions of Cladonia sect. Cladina species; they slide down and gather between the cushions. The growth form of these lichens therefore enhances their chances for survival in wooded areas. The combined influence of wind and rain The importance of some climatic factors can be understood only when they are observed together. During research on the microclimate of lichen habitats on an island in the North Sea the distribution of Physcia tenella on Sambucus was recorded. It could be shown that the development depended on the water relations, but that there existed no simple correlation with precipitation. The really important influence was the wind from the sea, which in open locations could direct the rain through the foliage to the trunk. In the lee of the dunes this did not happen. The combination of exposure to wind with the rainfall was a decisive factor for lichen occurrence. Dewfall and 'dry nights ' Another example of an environmental influence often omitted is dewfall, which is always important to lichens. In the course of a project, a transect
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