| dc.description.abstract | Lichens are observed to decline when shrub covers increases due to global warming and reduced grazing in alpine and arctic areas. However, lichens are still prominent in many mountain habitats where they cover large areas. This may be due to; a) their growth structure that might inhibit vascular plant recruitment (physical structure), b) their production of secondary metabolites that may inhibit germination of vascular plants (allelopathy), or c) their ability to grow in harsh environments unsuitable for vascular plants (low environmental requirement and high stress tolerance). We sowed seeds of 12 species in an alpine common garden experiment with different species of lichen cover. We also tested the chemical effects of the lichens on germination of the species in a growth chamber experiment. Our results show that lichens promote rather than inhibit vascular plants in their early life stages. Seedling emergence was higher within the lichen cover than on bare soil for all lichen species. Except for Cladonia stellaris the biomass of the seedlings was in general higher within the lichens compared to the seedlings on bare soil. The physical structure of C. stellaris cushions seems to inhibit the establishment of the vascular plant seedlings. Whereas thickness of the lichen cover in general affected the microclimate important for the seedling establishment, it could not explain the variation in soil moisture underneath the lichens. Although an overall strong effect of allelopathy could not be seen on seed germination in the lab experiment, the chemical structure of the lichens had species-specific effects on the plant species. Altogether, the physical structure of the lichens seems to be more important than the chemical structure for seedling emergence in field. | |
