Zur Kenntniss einiger Usneion-assoziationen in Europa
- Cite this article as:
- Barkman, J.J. Vegetatio Acta Geobot (1954) 4: 309. doi:10.1007/BF00301800
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Following the French-Swiss method of plant sociology (Braun-Blanquet) a study was made of the following epiphytic lichen communities: the subalpine Letharietum vulpinae Frey 1937 (Swiss Alps), the subalpine Parmeliopsidetum ambiguae Hilitzer 1925 (Swiss Alps) and the subarctic Parmelietum olivaceae (Frey 1927) Barkman 1954 (Sweden and N. Norway). All three of them are considered to belong to one and the same alliance, viz. the Usneion barbatae Ochsner 1928, which is discussed at the end, together with the other associations belonging to it, i.e. the Parmelietum furfuraceae Ochsner 1928 and the “Usneetum barbatae” Ochsner 1928. It is pointed out that the Cetrarion pinastri and the Cetrarietum pinastri of Ochsner (1928) are to be rejected, the latter being synonymous with the Parmeliopsidetum ambiguae. Furthermore it is made clear that the so-called Usneetum barbatae is not a natural, homogeneous unit and that consequently it will have to be split up in future research.
The characteristic species of the Parmelietum furfuraceae, as indicated by various authors, are critically reviewed.
The floristic composition and the characteristic species (“Charakterarten”) of the Letharietum, Parmelietum olivaceae and Parmeliopsidetum ambiguae will be evident from tables I, II and III respectively.
The aspect of the association is dominated by the bright yellowgreen wigs of Letharia vulpina, its structure is two-layered: a layer of fruticose lichens and a layer of foliaceous lichens, closely appressed to the bark (Parmeliopsistype of life forms). The association has a rather open character, its total cover averaging 60–70% of the tree surface. Often present non-characteristic species are Alectoria jubata, Parmelia furfuracea and Parmeliopsis ambigua. There is no great difference in composition between the vegetation on stems of Larix and that on Pinus Cembra. On branches of Larix different species may dominate, depending on the inclination of the branch: perpendicular drooping branches bear Letharia as a dominant species, on obliquely drooping branches (60–80°) Alectoria jubata dominates, on horizontal or slightly drooping branches (0–50°) Parmelia furfuracea dominates.
In the Alps the Letharietum only occurs on Larix (alive or dead) and on dead wood of Pinus Cembra, in Scandinavia it prefers Pinus silvestris. The association is restricted in the Alps to the Central Alps and to an altitudinal belt ranging from 1700–2100 m, that is within the belt of the Rhodoreto-Vaccinietum cembretosum to which it is confined. It only occurs near edges or glades of this forest type and avoids rigorously the bases of trees, which are snow-covered in winter. It prefers N-facing slopes and lives under conditions of intensive insolation (especially with regard to the ultraviolet fraction) in a continental-alpine climate with little precipitation, occasionally very dry air, sudden large fluctuations in temperature and very low winter temperatures.
The Letharietum colonizes the bark of young trees directly, without a pioneer stage of crustaceous lichens. Destructive factors causing rhytmical succession are: the constant peeling off of the bark of larch trees and strong winds tearing off the fruticose lichens.
The association is probably widely distributed in the inner chains of high mountain ranges in Europe and North America (for the distribution of Letharia vulpina and Parmelia austerodes in Europe see map II). It is absent however from the Scottish Highlands.
Usually Parmelia olivacea and P. sulcata are codominant, sometimes P. physodes too. Parmeliopsis ambigua is a constant species. The aspect is dominated by the glossy dark brown P. olivacea, the life form spectre by the Parmeliatype of foliaceous lichens. The structure is essentially one-layered. It is a very homogeneous association, with a wide distribution in continental subarctic regions of the Northern hemisphere, characterized by a dry, cold, sunny climate.
The Parmelietum olivaceae prefers the sunny elfin-woods of Betula pubescens var. tortuosa ranging from 300 to 700 m altitude in Sweden. It avoids the snow-covered trunk bases and the thin branches and twigs, the former being covered by the Parmeliopsidetum ambiguae, the latter by black veils of Alectoria jubata.
Usnea recedes into the background in the epiphytic vegetation of Sweden, being replaced here by a sociation of black Alectoria jubata or grey A. sarmentosa, the latter only in spruce forests with a very damp atmosphere.
Often present non-characteristic species are Parmeliopsis ambigua and Parmelia physodes. The association is rather heterogeneous, though less so than the Letharietum. Its structure is two-layered, the Cetrariatype and the Parmeliopsistype being the dominant ones. Its aspect is characterized by bright yellow colours (Cetraria pinastri and Parmeliopsis ambigua). It has a wide amplitude of substrata, such as to include most of the coniferous trees, as well as several Betula-species and a few Ericaceae. In the Swiss Alps a preference is shown for Pinus Mugho, in Scandinavia for Pinus silvestris and Betula. The Parmeliopsidetum thrives both on isolated pines, spruces and birches in wet subalpine bogs and in dry forests of Larix and Pinus Cembra, both on the stem bases in tall spruce forests and on twigs of very low Pinus Mugho-thickets above the timber line, both in dry and in wet mountain regions. In the Alps it ranges from 1200 to 2450 m. It is a photophilous association but it is seldom found high above the ground. In high, alpine habitats it needs snow protection in winter; in the lowlands its upper limit on the trees rises with increasing air humidity.
The Parmeliopsidetum is widely distributed in nearly all mountain ranges of Europe as well as in the plains of Northern Europe, including nearly all Scandinavia and the Northern half of Russia. Towards the plains of Central, Western and Southern Europe the association is gradually fading out, loosing its characteristic species one by one in various combinations; here it is gradually replaced by the Psoretum ostreatae.
Below 1200 m in the Alps tree trunks near glades or at the edges of forests are covered by the Parmelietum furfuraceae. Above 1200 m the Parmeliopsidetum ambiguae appears on the bases of the stems and the “Usneetum” on the branches. Above 1400 m the latter also replaces the Parmelietum furfuraceae on the middle part of the trunks. The Usneetum is in turn replaced by the Letharietum, first on the middle part of the trunks (above 1700 m), at still higher altitudes also on the branches.
Finally the alliance Usneion is discussed. It is pointed out that the five associations have several species in common, which partly find their optimum within the Usneion. Moreover an ecological affinity can be observed, for all associations are toxiphobous (very sensitive to air impurities), nitrophobous, acidiphilous, photophilous and restricted to cold-temperate climates (mountainous and boreal).