fulltext - DiVA

EINAR Du RIETZ took an active part in determiningthe composition and the names of the communities.Some of them may occur locally combinedwith a field layer or even with a tree layer rootedin crevices or between boulders (ALMQUIST 1929,ALBERTSON 1946a). The vegetation on wet rockand on shores has been omitted.The growth on rock 145Plant communities on strongly acid rockTHE RHACOMITRIUM LANUGINOSUM FEDERATION(RHACOMITRION).-To this federation belong acidophilousand photophilous societies and unions ofmosses and lichens, described, e.g., from southernFinland by H.AYREN (1914 p. 56) and from thecoasts of eastern Sweden by Du RIETZ ( 1925 a andd, 1932 b, 1950d). The federation plays an importantrole in forests of Pinus silvestris on rocky ground(Swedish : hdllmarkstallskogar) where it covers considerableareas (v. KRUSENSTJERNA 1945, p. 50).Fig. 2. Dicranum spurium forms characteristic epilithiccushions of densely crowded stems with incurved leaves,here together with the more strict-leaved D. rugosum(=D . undulatum). Alsike S of Uppsala. Aug. 1956. PhotoH. Jahn.Andreaea rupestris1Rhacomitrium heteTostichumA less strongly photophilousunionOften associated, yet more photophilous, are forinstance the following species: Dicranum scoparium,If.edwigia ciliata, Cladonia silvatica (sens. lat.), Corniculariaaculeata and Parmelia centrifuga (Fig. 1).Rhacomitrium lanuginosumDicranumspurium (Fig. 2)Cladonia silvaticaC. uncialisCetraria islandicaCladonia alpestrisC. rangiferinaC. silvaticaA union of mosses andlichens occurring on horizontalsurfaces. Otherlichens are Stereocaulonspp. and Gyrophora spp.An almost pure lichen"Lmion without othermosses than the big Di­C1'anum robustum (rarein southern Sweden)Fig. l. Parmelia centrijuga on an ice-scoured granitesurface and surrounding Cladonia alpestris - Callunavegetation. Fiby urskog, an old, not managed coniferousforest area W of Uppsala. Sept. 4, 1964. Photo P. Priitz.1 Species, indicative of unions or other communities oflower rank than federations stand to the left, other descriptivedetails to the right.A typical succession starts from crustaceous orumbilicariaceous lichens or occasional small cushionsof firmly attached mosses such as Andreaea, andpasses over Parmelia spp., Rhacomitrium lanuginosum,etc., ending in either Dicranum or Cladoniaspp. growing on a thin humus layer. In exposedlocalities this succession often has to start afresh,when the moss or lichen carpet is damaged orblown away.As the soil layer grows thicker some species becomemore and more common, e.g. Dicranum seaparium,Pohlia nutans, Polytrichum juniperinum. InActa Phytogeogr. Suec. 50