Succession of Epiphytic Bryophytes near Mountain Lake, Virginia

Abstract

Twenty-five species of mosses and nine species of liverworts, mostly facultative epiphytes, were present on the bases of 140 saplings of six tree species in a cove forest. Epiphytic communities on saplings showed greater mutual simi- larity than did those on trees. Only one epiphytic species was restricted to one host species and only eight species showed strong single-host preferences. Most epiphytic communities on saplings were very dissimilar to those on mature trees of the same species. Epiphytic communities on oak, maple, beech, yellow birch, black birch, and hemlock saplings were most similar to epiphytic communities on mature black birches, while those on beech saplings were most similar to those on mature beeches. By comparing epiphytes on saplings and trees, successional trends could be inferred that led to the more sharply delimited host specificities of epiphytes on trees. These trends included: the persistence and expansion of some pioneer species, the disappearance of others, and the appearance of additional species that were not present on saplings; these additional species often showed strong host preferences and (especially on oak and maple) mesophytic growth- forms. The composition of epiphytic bryophyte communities on a tree changes as the tree ages. Such succession is probably caused by the growth of the tree and accompanying changes in bark characteristics and microclimate (Barkman 1958; Yarranton 1972). Host specificity of epiphytic bryophytes may be poorly developed both in very young trees where species-specific bark characteristics have not yet developed and on very old trees where differences have been obscured by the action of climatic factors over time (Barkman 1958). The objective of this study was to investigate the succession of epiphytic bryophytes by the indirect but convenient method of comparing species composition and host pref- erences of bryophytes on six species of saplings (red oak, red maple, beech, yellow birch, black birch, and hemlock) with those previously described (Studlar 1982) for mature trees of the same species from the same cove forest. Growth-form spectra of epiphytic com- munities on saplings and trees were also compared, since studies of terrestrial bryophytes have suggested correlations between changes in growth-form spectra and changes in mi- croclimate during succession (Birse & Gimingham 1955). METHODS Sampling methods. The study area, a cove forest along a creek (Pond Drain) near Mountain Lake, Virginia, was described in another study (Studlar 1982). Epiphytic bryophytes were collected from the bases (0-1.8 m) of 20 saplings for each of six host species at Pond Drain: Quercus rubra L. (red oak), Acer rubrum L. (red maple), Fagus grandifolia J. F. Ehrh. (beech), Betula alleghaniensis N. L. Britt. (yellow birch), Betula lenta L. (black birch) and Tsuga canadensis (L.) Carr. (hemlock). Saplings were defined as having diameters at breast height (DBH) of no more than 10 cm. The only