Influence of Stand Age And Structure on the Epiphytic Lichen ...

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178 THE LICHENOLOGIST Vol.24 net photosynthesis even without liquid water (Lange et al. 1986,1988). Consequently stem flow is likely to be <strong>of</strong> more importance for nutrient availability than for the water balance <strong>of</strong> the lichen thallus. The occurrence <strong>of</strong> crustose species more frequently on spruce trunks could be a compromise between competitive pressure <strong>of</strong> faster-growing growth forms and unfavourable light conditions, analogous to the observations <strong>of</strong> Jesberger & Sheard (1973) and Kantvilas & Minchin (1989), who proposed the roughness and dryness <strong>of</strong> the bark as environmental factors creating room for crustose species. Time and height-time interaction were found to be consistently important for the distribution <strong>of</strong> macrolichens on black spruce by Yarranton (1972), who stated that the effect <strong>of</strong> absolute age is merely a function <strong>of</strong> the increasing height <strong>of</strong> the trees, which alters the microclimate <strong>of</strong> the stand. In the present work the average height <strong>of</strong> the stand, as indicated by the length and close proximity <strong>of</strong> the arrow to the first axis in the pine ordination (Fig. 2), is closely related to the pattern <strong>of</strong> community variation, although the distinction between the stand age and the average height is too small to permit separation <strong>of</strong> the effects <strong>of</strong> these variables on the distribution <strong>of</strong> individual species by visual interpretation <strong>of</strong> the plot pattern. Overall, the r-values for the regression coefficients <strong>of</strong> these variables (Table 4) clearly indicate that average height has only a small independent function with respect to community variation and that it fuses into the effect <strong>of</strong> stand age and other changes in the structure <strong>of</strong> the stand and individual trees. Interspecific morphological variability, especially in the surface area to weight ratio, is known to be significant for the ecology <strong>of</strong> lichens through its direct influence on water balance (Larson & Kershaw 1976; Kershaw 1985). Usnea filipendula and B. capillaris, which represent slender and pendulous growth forms, clearly prefer denser stands than the more shrub-like, robust species B.furcellata and U. hirta. Bryoriafuscescens, which is quite common in all kind <strong>of</strong> stands, could be considered indifferent in this respect. The taxonomy <strong>of</strong> B. fuscescens is not clear, however, and it is considered to be a taxon containing several forms (Brodo & Hawksworth 1977) that may have different ecological demands. The growth form <strong>of</strong> a species is closely linked to the concept <strong>of</strong> ecological strategy among epiphytes. Rogers (1988,1990) classified lichen species according to Grime's (1979) triangular ordination model, linking fruticose and foliose growth forms with a competitive strategy and crustose ones with stress-tolerant and ruderal strategies. As suggested by Rogers & Barnes (1986), the ecological strategy <strong>of</strong> a lichen is related to the substratum type, with short-term substrata open to colonization only by ruderal species. In the present material a ruderal strategy concerning successional change in the epiphytic lichen communities could only be associated with such species as Cetraria sepincola and Lecanora spp., which give way to others after colonizing a new surface on the bark <strong>of</strong> pines. Overall, the mean strategy <strong>of</strong> the lichen species with increasing stability <strong>of</strong> the substratum and environment during natural succession could be assumed to shift slightly from ruderality towards the competitive pole (Rogers 1988). Consequently, species such as Cladonia spp. and U. filipendula, which are abundant in dense, old pine-stands, are considered to be good competitors
1992 Epiphytic lichens—Hyvdrinen et al. 179 owing to their growth form, while the crustose species preferring acidity, such as the family Caliciaceae and Lecidea spp., could be classified as stress-tolerant. Special thanks are extended to Mr O. Vitikainen and Dr L. Tibell for their help in identifying some <strong>of</strong> the lichen specimens. We also wish to thank Dr J. Oksanen and Mr T. Muotka for reading the manuscript and making constructive suggestions and Mr Malcolm Hicks, M.A. for revising the language. The research was supported by the Academy <strong>of</strong> Finland. REFERENCES Adams, D. B. & Risser, P. G. (1971) Some factors influencing the frequency <strong>of</strong> bark lichens in north central Oklahoma. American Journal <strong>of</strong> Botany 58: 752-757. Ahlner, S. (1948) Utbredningstyper bland nordiska barrtradslavar. Acta Phytogeographica Suecica 22: 1-257. Ahti, T. (1964) Macrolichens and their zonal distribution in boreal and arctic Ontario, Canada. Annales Botanici Fennici 1: 1-35. Ahti, T., Hamet-Ahti, L. & Jalas, J. (1968) Vegetation zones and their sections in northwestern Europe. Annales Botanici Fennici 5: 169—211. Armstrong, R. A. (1990) Dispersal, establishment and survival <strong>of</strong> soredia and fragments <strong>of</strong> the lichen Hypogymniaphysodes (L.) Nyl. New Phytologist 114:239—245. Barkman, J. J. (1958) Phytosociology and Ecology <strong>of</strong> Cryptogamic Epiphytes. Assen: VanGorcum. Bitterlich, W. (1948) Die Winkelzahlprobe. Allgemeine Forst und Holzwirtschaft Zeitung 59: 4-5. Brodo, I. M. & Hawksworth, D. L. (1977) Alectoria and allied genera in North America. Opera BotanicaAl: 1-161. Clements, F. E. (1916) Plant succession: an analysis <strong>of</strong> the development <strong>of</strong> vegetation. Washington: Carnegie Institute. Culberson, C. F. & Kristinsson, H.-D. (1970) A standardised method for the identification <strong>of</strong> lichen products. Journal <strong>of</strong> Chromatography 46:85—93. Esseen, P.-A. (1981) Host specificity and ecology <strong>of</strong> epiphytic macrolichens in some central Swedish spruce forests. Wahlenbergia 7: 73—70. Eversman, S., Johnson, C. & Gustafson, D. (1987) Vertical distribution <strong>of</strong> epiphytic lichens on three tree species in Yellowstone national park. Bryologist 90:212-216. Grime, J. P. (1979) Plant Strategies and Vegetational Processes. London: Wiley. Hale, M. E. (1965) Vertical distribution <strong>of</strong> cryptogams in a Red Maple Swamp in Connecticut. Bryologist 68: 193-197. Halonen, P., Hyvarinen, M. & Kauppi, M. (1991) Epiphytic lichens in relation to climate in mesic heath forests <strong>of</strong> the middle boreal subzone. Lichenologist 23: 61-72. Hill, M. O. (1973) Reciprocal averaging: an eigenvector method <strong>of</strong> ordination. Journal <strong>of</strong> Ecology 61:237-249. Jesberger, J. A. & Sheard, J. W. (1973) A quantitative study and multivariate analysis <strong>of</strong> corticolous lichen communities in southern boreal forests <strong>of</strong> Saskatchewan. Canadian Journal <strong>of</strong> Botany 51:185-201. Kalela, A. (1961) Waldvegetationszonen Finnlands und ihre klimatischen Paralleltypen. Archivum Societatis Zoologicae Botanicae Fennicae Vanamo 16 (Suppl): 65—83. Kalgutkar, R. M. & Bird, C. D. (1969) Lichens found on Larix lyallii and Pinus albicaulis in southwestern Alberta, Canada. Canadian Journal <strong>of</strong> Botany 47:627-648. Kantvilas, G. & Minchin, P. (1989) An analysis <strong>of</strong> epiphytic lichen communities inTasmanian cool temperate rain forest. Vegetatio 84: 99-112. Kershaw, K. A. (1964) Preliminary observations on the distribution and ecology <strong>of</strong> epiphytic lichens in Wales. Lichenologist 2: 263-276. Kershaw, K. A. (1985) Physiological Ecology <strong>of</strong> Lichens. Cambridge: Cambridge University Press. Koskinen, A. (1955) Uber die Kryptogamen der Bdume, besonders die Flechten, im Gewdssergebiet des Pdijdnne sowie an den Flussen Kalajoki, Lestijoki und Pyhdjoki, Floristische, soziologische und okologische studie I. Helsinki: author's edition. Lange, O. L., Kilian, E. & Ziegler, H. (1986) Water vapour uptake and photosynthesis <strong>of</strong> lichens: performance differences in species with green and blue-green algae as phycobionts. Oecologia 71:104-110.
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