Usnea longissima Ach.

Huldrestry

World distribution: Usnea longissima is restricted to the boreal coniferous region where it has an incompletely circumpolar distribution, with occurrences in Europe, Asia, and North America (Motyka 1936-38, Ahti 1977a). The distribution was previously considered to be continental (Ahlner 1948, Gams 1961). With additional recent records from Spain (Ottosson 1968) and from oceanic parts of Norway (Jørgensen & Øvstedal 1975, Gauslaa et al. 1992), however, the European distribution conforms with Schauer's (1965) distribution type 'nordmitteleuropäisch-ozeanisch'. Ahti (1977a) also stressed the oceanic tendency of this species, as it is more common near coasts and not present in the highly continental parts of the world. The Scandinavian distribution was mapped by Ahlner (1948); updated maps from Sweden and/or other data on distribution are given by Esseen & Ericson (1982), Esseen (1991), and Andersson & Williamson (1993). Declining populations of U. longissima were reported from Scandinavia already by Ahlner (1931b), and from other parts of Europe by Lettau (1911) and Gams (1961). The species is now extinct or threatened in many European countries (Bibinger 1970, Esseen et al. 1981, Esseen & Ericson 1982, Ruoss & Clerc 1987, Wirth 1976, 1987). It is listed as extinct from the EU (Serusiaux 1989), but recent collections has been distributed from Italy (Obermayer 1996). Norway has the largest and most vital populations in Scandinavia (Gaarder et al. 1991), as well as in whole of Europe

Ecology: Results. The most frequent host tree was Picea abies, but the species was often abundant on deciduous trees as well. On Picea abies it was often twisted around branches that had green needles, without direct contact with the bark. The few saxicolous records represented temporary, secondary habitats in sites where the species was highly abundant. Usnea longissima was normally found on old trees in old-growth forests dominated by Picea abies. It was only found on young trees in localities with large, vital populations on nearby old trees. Two different types of habitats were frequently observed: Old spruce forests with northern to eastern exposure (hill localities), and forested canyons with running water. Stands were normally more open than silvicultural, managed stands, with a low basal area of 17.8 ±1.4 m2/ha (mean ±standard error of mean; n=33, Y. Gauslaa & G. Gaarder, unpubl. data). Usnea longissima was frequently found in forests where gentle selective fellings were practised in the past, as recognized by frequent lack of old decaying logs. pH measurements of twigs of the most common host, Picea abies, showed that U. longissima tolerates a low bark pH (4.13 ±0.07, n=33, Y. Gauslaa, unpubl. data). Localities with U. longissima frequently contained other interesting macrolichens as well, e.g., Alectoria sarmentosa, Bryoria bicolor, B. nadvornikiana, B. tenuis, Hypogymnia vittata, Lobaria pulmonaria, L. scrobiculata, and Platismatia norvegica. Canyon localities also contained Ramalina thrausta and several rare members of Caliciales, locally also Menegazzia terebrata and Cetrelia olivetorum. The southernmost localities and the west coast localities additionally contained oceanic species like Arthonia vinosa, Degelia plumbea, Lobaria amplissima, Nephroma laevigatum, Normandina pulchella, Pannaria conoplea, P. ignobilis, P. rubiginosa, Peltigera collina, Sticta sylvatica, and Thelotrema lepadinum. Discussion. Usnea longissima does not seem to favour Picea abies as substrate over other trees, although it shows a strong preference for Picea forests. G. Gaarder (unpubl. data) demonstrates that the distribution of U. longissima on the different trees corresponds to the tree species distribution within the stands. One of the vital localities was a mixed Quercus sp. and Pinus sylvestris stand. The species therefore appears less host specific than in Sweden (Ahlner 1931b, Esseen 1981), probably because of a more humid climate. It has never been recorded outside forests. The species may be considered as an indicator of old-growth forests. In Sweden most trees have an age of 80-150 years, with a maximum of 270 years in Picea forests with U. longissima (Esseen et al. 1981). Haugmoen (1952) concluded that U. longissima well tolerates the selective fellings that were previously practised, a conclusion supported by the observation of stumps in several visited stands. Clear-cutting was introduced in Norway in the 1950's. Usnea longissima localities seem mostly to be fire-free refugia, as in Sweden (Esseen et al. 1981). Fire is usually avoided because of local moist soils due to northern and eastern aspect, but probably also because of high air humidity (Esseen et al. 1981). Gams (1961) classified U. longissima as a strongly mist-depending lichen. Usnea longissima often has a patchy occurrence, even in uniform habitats. This has been explained by its shorter dispersal distances compared to other thread-like lichens (Esseen 1985). The short dispersal distance is unfavourable in a forested landscape fragmented by clearings (Esseen & Ericson 1982). According to Gauslaa et al. (1992), Usnea longissima may have immigrated relatively recently to parts of its present distribution area in eastern Norway. They regard the few highly oceanic forests along the western coast (especially 1386 with luxurious populations of the species on Quercus sp. and Pinus sylvestris) as probable refugia in a part of the country where extensive deforestation occurred in earlier periods. Picea abies creates a moist microclimate, and its immigration to eastern Norway 1000-2500 years ago (Hafsten 1992) may have enabled U. longissima to extend its distribution area eastward into areas with a drier macroclimate, as has been indicated for Platismatia norvegica (Ahlner 1948) and Bryoria smithii (see this species). Usnea longissima tends to be most common in suboceanic hills of eastern Norway, as it is in Sweden (Esseen et al. 1981)

Threats: Results. Recorded threats were forestry (171), air pollution (138), and land development (2). Discussion. Clear fellings is the most frequently recorded cause of extinction, reduced vitality or abundance. Fellings of neighbouring stands have also been demonstrated to have affected U. longissima. The species disappeared within 5 years from one locality in Totenåsen (2981) because of neighbouring stands were cleared. Damage has frequently been reported near clear fellings, demonstrating the need for buffer zones around the localities. The southernmost intact locality in Vestfold (596) have an intact forest environment with several other probable indicators of canopy continuity over a relatively large area. Only blackish and weak thalli of U. longissima were found, suggesting that some kind of air pollution may threaten the population. In the other old Vestfold localities, forestry alone could explain the extinction, as clearings were constantly present. There seems to be a general agreement that forestry is the main threat (Lettau 1911, Ahlner 1931b, Gams 1961, Esseen et al. 1981, Esseen & Ericson 1982, Ruoss & Clerc 1987). Damage to intact neighbouring stands bordering a clearfelled area have also been reported from Sweden (Esseen & Ericson 1982). However, Olsen & Gauslaa (1991) found that fellings alone could not explain the large loss of localities in Nordmarka, a forested area north of Oslo, and concluded that air pollution is also likely to play a role. Esseen et al. (1981) reached a similar conclusion for Sweden

Status: The species was investigated in 48 old localities. It was found in 18 localities, regarded as extinct in 27, and of uncertain status in 3. 152 new localities were discovered. Reduced vitality and/or abundance was observed in 5 of the 18 old and intact localities. It is difficult to give an exact number of intact localities, because several of the 164 localities discovered in the 1990's are already destroyed. Populations fragmented or reduced by fellings were recorded in as many as 28 of the localities discovered after 1990. Seventy-nine percent of the localities have been discovered after 1950, 48% after 1970, and as much as 37% after 1990, mainly because the species has recently been intensively searched for in new localities. The apparent increase in known intact localities reflects sampling history rather than trends in the dynamics of distribution and abundance. A scatter diagram of latitude and altitude indicates that the original distribution area included most of the forested land in eastern Norway situated between 59° and 62°N from an altitude of 100 to at least 800 m. The apparent shift in preference to higher altitudes and latitudes during the recording history of U. longissima in Norway probably reflects merely the easier access to areas far away from botanical institutions and public transportation. The early botanists collected forest lichens mainly in the southern lowlands and close to roads. Nearly all these old localities seem to be destroyed, while forests previously too far away for collectors and loggers still fragmentarily contain intact habitats. At present the previously unaccessible forests are rapidly being exploited. The gap in the distribution along the Swedish border represents an area not much visited by the early lichenologists, and few old-growth forests are known from this area. No intact localities were found in the southern parts of Vestfold, that was previously a center for U. longissima. The species has been re-mapped in parts of Nordmarka (Olsen & Gauslaa 1991), a forest area north of Oslo that had rich and healthy populations in 1951 (Haugmoen 1952); it was not found in any of the 67 localities that were intact 1951, but occurred 7 apparently newly discovered localities. The following localities are within nature reserves: Akershus: 1391, 2642; Oppland: 484, 495, 1394, 507, 492, 1395, 1396, 3164; and Sogn og Fjordane: 1386 (temporarily protected). None of the largest U. longissima populations are protected

Specimens in other herbaria, litterature, etc.