Succession of epiphytic bryophytes in a Quercus pyrenaica forest from the Spanish Central Range (Iberian Peninsula)

Succession among epiphytic bryophytes is studied in a deciduous forest of Quercus pyrenaica Willd. from the Spanish Central Range, with the objective of assessing fluctuations of species and life-forms throughout the life-span of trees. For this purpose, an indirect method is used, which consists of studying epiphytes occurring on different-aged trees. Additionally, a new index, called the "Index of Ecological Significance (IES)" and derived from a combination of relative frequency and mean cover, is used to evaluate the ecological importance of taxa in epiphytic habitats. Results show qualitative and quantitative changes in epiphytic community composition during the tree life-span. Young trees are colonized by pioneer species. Some of them become more extensive on older trees, while others disappear, and a group of additional species occur exclusively on old trees. Similarly, species richness and bryophytic cover increase with tree age, while community composition and structure change, due to species and life-form replacement. These changes take place in a similar way on bases and trunks, although the former are always bryofloristically richer. As for successional patterns, both bases and trunks feature a main lineal and allogenic series, which is completed by a secondary cyclic and autogenic series that is restricted to old trees.