Ecology of lichens in boreal coniferous forests with reference to spatial and temporal patterns

Detta är en avhandling från Umeå : Umeå universitet

Sammanfattning: The thesis deals with the ecology of lichens in two contrasting types of forest, epiphytic lichens in old Picea abies forest of the fi re-refugia type and epigeic as well as epixylic lichens in a successional sequence of fire- susceptible Pinus sylvestris forests. Results in five separate papers form the basis for a discussion of general patterns of dispersal, succession and life strategies in lichens. The study sites were located in Medelpad and Väs­terbotten, in the central and northern part of Sweden, respectively.Special attention has been paid to the rare, pendulous, spruce-1ichen Usnea longissima and the coexisting lichen species. U. longissima is largely restricted to north-facing hill slopes covered with old, mesic spruce forest that is characterized by a very long continuity not disturbed by fire. A mar­ked decline in the number of sites with U. longissima was found. The decline was mainly due to the effect of different forestry practices as the species is very sensitive to environmental disturbances.The epiphytic lichen vegetation of six tree species occurring in the spruce forest is described. Clear successional trends with increasing tree size were • obtained for Alectoria sarmentosa, Bryoria fuscescens coll., B. nadvornikiana, Usnea filipendula' and U. subflorida'na, to a lesser extent for Bryoria capii-“" laris while U. longissima had no relationship to tree size or age.TTstudy of the litterfall of macrofragments of epiphytic lichens showed that thallus fragments were dispersed throughout the year with late autumn, winter and early spring as the most critical periods. It is suggested that dispersal through thallus fragmentation is more important in fruticose than in foliose species and that U. longissima has a shorter range of propagule transport than the other species of Alectoria, Bryoria and Usnea studied. The latter proposition was supported through a study of the horizontal patterns of lichen occurrence in the spruce forest.It is shown that the diversity in ground vegetation, after an initial in­crease, declines with succession in the pine forests. A mechanism of succes­sion in ground vegetation is presented which suggest that variations in habi­tat heterogeneity, i.e. the diversity of substrates caused by the initial dis­turbance and the stand development, largely determines diversity changes dur­ing succession. Trends of increasing thallus size, increasing size of asexual reproductive propagules and increased competitive ability with succession formed the basis for recognizing three types of strategies in Cladonia»It is concluded that lichens have features that are compatible with the r-K continuum and that they are variously adapted to both the stability of the substrates and that of the forest as a whole.