World distribution: Evernia divaricata is a widespread circumboreal species, occurring in central Asia and Siberia (Ahlner 1948, G. Awasthi 1982), the Rocky Mountains and Alaska in North America (Ahlner 1948, Bird 1974, Thomson 1984), and in Europe (Ahlner 1948, Poelt 1969). It is regarded as hemiboreal to oroarctic by Goward & Ahti (1992). In Europe, the species is known from the Iberian peninsula to the Ural mountains; it is absent in the most Atlantic regions (Ahlner 1948, Poelt 1969). It is, however, most common in two separate regions, namely the Alps and Fennoscandia (Barkman 1969). It is locally common in the Alps (Nimis 1993). The species is not common but widespread in Sweden and Finland, with most records in the eastern parts of both countries (Ahlner 1948, Ingelög et al. 1987)
Ecology: Results. Recorded substrates are Picea abies (15), Pinus sylvestris (9), rock (6), Sorbus aucuparia (2), Betula pubescens (2), Alnus incana (1), Betula pendula (1), Juniperus communis (1), Populus tremula (1), and Salix caprea (1). Habitat information is given for 17 localities. There are 9 records from mixed coniferous forest (Picea abies and Pinus sylvestris), 9 from Picea forest, 3 from Pinus forest and 1 from thermophilous deciduous forest. Thirteen localities are situated in humid forests close to rivers, waterfalls or brooks, 3 in forested mire, and 2 in swamp forest. One locality is situated in open forest in a south-facing scree, and one is on a large south-facing rock wall close to a road. Discussion. Most Norwegian localities are from mixed coniferous forests with ample light, but the species is usually protected from direct sunshine during the part of the day when the sun is high. G. Nilsson (1929) and Ahlner (1948) found E. divaricata mainly on Picea abies, but some other trees are also mentioned, especially Pinus sylvestris. When the species occurs on Pinus sylvestris, it is usually also growing on Picea abies in the surroundings (Ahlner 1948). The species grows mainly on the lower branches or directly on the trunk, often 1-3 m above the ground (Ahlner 1948, Haugan et al. 1994). In the Alps, the species often grows on the branches of conifers with an open crown (Nimis 1993). Evernia divaricata seems to prefer old, slow-growing trees (Hermansson et al. 1988, Haugan et al. 1994). Measurements of trees carrying the species in two Norwegian areas showed 140 to c. 300 years (Haugan et al. 1994). According to Ahlner (1948), saxicolous populations of the species are rare. It is also terricolous in alpine areas in North America (Bird 1974) and the Alps (Nimis 1993), and in sanddunes in Sweden and the Netherlands (Ahlner 1948). The species prefers moist and swampy forests, especially forests close to mires, along brooks, and in ravines (Ahlner 1948, Ingelög et al. 1987, Hermansson et al. 1988, Goward & Ahti 1992, Sjöberg & Ericson 1992, Haugan et al. 1994). In Central Europe, the species occurs in humid montane coniferous forests (Wirth 1987, Nimis 1993). Goward & Ahti (1992) mention good light conditions as important for the species. Evernia divaricata often grows in the low-laying places in the terrain, according to Ahlner (1948) probably because of vulnerability to strong winds. Its preference for concave landscape forms may, as well, be a response to forest fire rather than wind. Haugan et al. (1994) investigated a large area where E. divaricata occurs as one of the dominant pendulous species, and found that the species was absent within a smaller area which burned in 1905. Goward & Ahti (1992) also suggest that the local distribution of E. divaricata may be limited by forest fires. Evernia divaricata rarely develops soredia or apothecia (Ahlner 1931a, 1948), and the species is apparently anemochorously dispersed by thallus fragments. The dispersal is therefore probably slow (Haugan et al. 1994), and the species seems to be an indicator of canopy continuity in Scandinavia (Hermansson 1990, Karström 1992b, Bredesen et al. 1993). Associated epiphytic macrolichens in Scandinavia include Alectoria sarmentosa, Bryoria nadvornikiana, B. capillaris, B. fuscescens, B. implexa, Hypogymnia bitteri, Ramalina thrausta, Usnea chaetophora, U. filipendula, U. longissima, and U. subfloridana agg. (see Hermansson et al. 1988, Karström 1992b, Haugan et al. 1994)
Threats: Results. Recorded threats were logging (22), road construction (6), ditching (3), air pollution (3), development of hydroelectric power (2), and abrasion (1). Discussion. The Norwegian populations are apparently mainly threatened by clear felling. The richest localities have already been drastically reduced by clear felling after the fieldwork in 1993 (1338 and 2767). Localities 21, 30, 2748, and 3096 may also have been seriously affected by logging in 1993-1994. Already Ahlner (1948) suggested that E. divaricata was threatened by forestry. In Sweden, the number of localities has decreased, and the species is regarded as vulnerable (Aronsson et al. 1995). In Finland, where the species occurs in primeval forests, it has declined drastically, but the populations are not yet in serious danger (Rassi & Väisänen 1987). The species has declined also in Germany, mainly due to logging and air pollution (Wirth 1976, 1987)
Status: Seventeen old localities were investigated; of these the species was found at 7 and apparently extinct from 10 localities. Eight new localities were discovered. One population is situated within a nature reserve (2124). Two recently discovered localities in Oppland (1338, 2767) comprise very large populations; here the species grows on 5000-20000 trees. The richest locality (1338) is in old forests along the river Begna, where E. divaricata occurs in a c. 5 km long and up to 500 m broad region. Locality 2767 is a old forest area, c. 2 km2 large. In both localities, E. divaricata is one of the dominant pendulous species, especially in the most humid parts of the forests (Haugan et al. 1994)
Notes: The rejected locality (1722) is a dry pine forest close to the upper limit for coniferous forests. This is an unusual habitat for the species, and since the collector also collected E. divaricata on another locality in Vågå (1723) the same day, we believe that 1722 is an error due to exchange of locality data..
Specimens in other herbaria, litterature, etc.