| dc.description.abstract | Dead wood remnants and other dead organic material in dry and semi-shady environments underneath overhanging rock walls and boulders, constitute a specific habitat for a number of lichens. We describe this peculiar habitat and its associated diversity of lichens in Norway. This element has been poorly known apart from a small number of experienced people working with canyon inventories, and publications are few. The habitat belongs to the NiN nature type «cave and rock overhang». It is characterized both by extreme ecological stability related to microclimate, substrate, and aridity, and is almost unaffected by the local complex environmental variables (LKMs) of dryness, water seepage, and water spray. In Norway this habitat is mostly found in larger river canyons, to a lesser extent in steep hillsides, more rarely in other topographical situations. Well-developed localities are mostly found in closed-canopy old-growth forests, and mostly close to the river in canyons or in the lowest parts of steep hillsides facing north to east. So far, at least 43 lichen species are known associated to this habitat in Norway. Most likely the number will rise as more systematic and comprehensive fieldwork is conducted. A relatively high proportion of the species are red-listed, 13 in all, and for some of the species the populations in this habitat are of national and international importance. The species diversity is clearly highest in inland valleys with a continental climate, while the element is much less developed in more oceanic regions. The habitat and its species, when well-developed, are limited to very small areas in very specific topographical situations. In addition, it is dependent on more or less old-growth forest, extreme ecological stability, and very long formation time for new substrates. Thus, the habitat and its associated species have probably had a strong decline historically. Today the rate of decline is probably lower, but especially construction of new roads, along with clear-cut forestry, and to some extent hydropower development, remain ongoing threats. Therefore, this internationally conservation-worthy habitat and parts of its species associations should be considered as threatened in Norway. | en_US |
