Scots pine-lichen forests in the middle and northerntaiga of European Russia

Following the dominant-floristic approach to vegetation, 9 syntaxa of Scots pine(Pinus sylvestris L.) forests and open woodlands with fruticose lichen ground coverdominated by Cladina spp. (C. arbuscula, C. rangiferina, and C. stellaris), namely 2associations with 5 subassociations and 8 variants, were distinguished in the northernand middle taiga of European Russia (all the units are given in the synoptic table). Allthe communities are subject to periodic fire; the postfire succession differences due tolichen ecology and canopy density are briefly discussed at the beginning of the paper ingeneral accordance with the classical works by K.W. Kershaw.The Cladino-Pinetum (P.) with no dwarfshrub layer or that of Calluna vulgariswith the admixture of Vaccinium vitis-idaea is a southern and middle taiga syntaxon,also distributed in the south of the northern taiga subzone. It is subdivided into 2subassociations, the typicum and polytrichetosum communis, growing on sand andon silicate rock, respectively. The petrophytic subass. polytrichetosum is distinguisheddue to local paludification in the cliff «pockets» which results in the presence ofPolytrichum commune and Sphagnum spp. sect. Acutifolia. The rock plants Polypodiumvulgare and Cladonia macrophylla are also typical together with Juniperus communisand Hieracium umbellatum.The Empetro-Cladino-P. is the northern taiga unit with a dwarfshrub layer withthe participation of the hypoarctic ericoid species like Empetrum hermaphroditum,Vaccinium uliginosum, and Ledum palustre, also with the moss Dicranum fuscescens.It is subdivided into the 3 subordinate subassociations, the typicum and betuletosumczerepanovii occurring on sand in the southern and the northern belts of the subzone,respectively, and the arctoparmelietosum restricted to rock outcrops throughoutthe subzone. The northernmost subass. betuletosum is typical of the presence of thearctic-alpine lichens like Stereocaulon paschale, S. alpinum, Nephroma arcticum,and Flavocetraria nivalis, also the hypoarctic plants like Betula czerepanovii andArctous alpina, and the northern-boreal moss Dicranum drummondii. The petrophyticsubass. arctoparmelietosum is marked by the dark-coniferous forest mesophytes likeTrientalis europaea and Linnaea borealis. The both petrophytic subassociations aretypical of Betula pendula, Avenella flexuosa, Ptilidium ciliare, Dicranum scoparium,and Racomitrium microcarpon; Arctoparmelia centrifuga appears dominant but notdeterminant on bare rock.The association distribution mainly follows the subzonal pattern, although theranges of both the associations overlap in the southern belt of the northern taigasubzone. The subassociations differ due to both the climate (the Empetro-Cladino-P.typicum vs. betuletosum czerepanovii), and the bedrock (the Fennoscandian petrophyticCladino-P. polytrichetosum and arctoparmelietosum vs. psammophytic units withwider distribution). Variants of the psammophytic subassociations are subdividedinto the western and the eastern ones due to presence/absence of the same group ofspecies (Calluna vulgaris, Festuca ovina and Cladonia cornuta, common to the westand replaced by Calamagrostis epigeios and Chamaenerion angustifolium to the eastof the Mezen R.). Whereas the northern-boreal petrophytic subassociation variants aregoverned by previous fire intensity: after the most severe fire, the var. Arctostaphylosuva-ursi is observed.

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