Epiphytic Lichens on Populus tremula: Implications for Conservation
This is the Abstract of the dissertation thesis, as titled above, and submitted by Henrik Hedenås in February 2002.
Henrik Hedenås
Department of Ecology and Environmental Science
Umeå University
SE-901 87 Umeå
Sweden
Email: henrik.hedenas@eg.umu.se
Abstract
Aspens in the Fennoscandian boreal landscape are strongly associated with post-fire successional habitats. Due to forestry and changed disturbance regimes the occurrence of aspen has declined markedly and as a consequence the occurrence of several of its associated species has declined. This thesis is focused on epiphytic lichens connected to aspen, and aspects of importance for their future conservation. I have studied how they are affected by dispersal mode, stand characteristics and forestry.
Data on lichen species composition in stands of different age and location, showed that old stands in the forest housed a large number of threatened cyanolichens, neither present in the agricultural landscape nor in younger stands. However, forest stands were often too dense or shady for several green-algal species that instead are confined to aspen in the agriculture landscapes.
Data on disease incidence of the lichen parasite, Abrothallus
suecicus, on its host Ramalina sinensis, showed an increasing severity with increasing stand age, and
that very high disease levels are reached in old stands.
Data on lichen dispersal mode showed that there was a difference in distribution, both at landscape and at stand level, between asexually and sexually dispersed species. First, sexually dispersed species are over-represented among epiphytic lichens that are confined to aspen, particularly in younger stands. In contrast, asexual dispersal modes prevails among late-successional aspen specialists, as well as species confined to goat willow and aspen. Second, of five studied species two sexually dispersed species were more aggregated than the aspen trees, while the distribution of the three asexually dispersed species more or less mirrored the spatial pattern shown by the substrate.
A study of the response of five epiphytic lichens to an alternative silvicultural practice, including a 50% removal of the standing volume, showed a clear response four years after
treatment, with reduced vitality and radial growth. Two crustose lichens showed severe
damages, one cyanolichen showed intermediate damages, while two cyanolichens were only marginally affected. Growth rate in average decreased for all five species by the treatment, but the reduction was only significant for three species.
In order to preserve the unique lichen flora that is associated with aspen there is an urgent need to conserve late-successional stands, and enhance a continuous creation of new aspen stands in the forest landscape. Further, forest stands and agricultural stands are not exchangeable. This implies that not only stand age but also habitat quality must be considered in future conservational programs.
Lichens on aspen - related pages
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