W19 - Juniperus Communis Ssp. Communis-Oxalis Acetosella Woodland

Summary

Synonymy

Birch-juniper wood Tansley 1939; Juniper heath Pigott 1956a; Juniper scrub Poore & McVean 1957; Juniperus-Thelypteris nodum McVean & Ratcliffe 1962; Fern-rich juniper scrub McVean 1964a; Thelypterido-Juniperetum Graham 1971; Juniperus-Vaccinium nodum Huntley & Birks 1979a; Juniperus-Campanula nodum Huntley & Birks 1979a; Trientali-Juniperetum Birse 1980; Trientali-Betuletum pendulae Birse 1982 p.p.

Constant species

Juniperus communis ssp. communis, Agrostis canina ssp. montana, A. capillaris, Galium saxatile, Luzula pilosa, Oxalis acetosella, Vaccinium myrtillus, Hylocomium splendens, Thuidium tamariscinum.

Rare species

Linnaea borealis, Orthilia secunda, Potentilla crantzii, Pyrola media.

Physiognomy

Juniperus communis ssp. communis is always the most abundant woody species in this community, though some stands have an open over-canopy of birch, almost invariably Betula pubescens and usually ssp. carpatica, with multi-stemmed trees typically less than 10 m high and showing bushy, contorted growth (Forbes & Kenworthy 1973, Huntley & Birks 1979a; Birse 1980,1982). Increased amounts of birch, over juniper and the associated flora here, generally mark transitions to the Quercus-Betula-Dicranum woodland or, on somewhat less acidic and more fertile soils, the Quercus-Betula-Oxalis woodland. Such transitions often take the form of ill-defined mosaics (a feature especially well seen in the east-central Highlands of Scotland: Ratcliffe 1977, Huntley & Birks 1979a, b) and then separation of the different communities may be a question of the proportions of the two woody species. Similar problems can arise with Pinus sylvestris, which can occur here as isolated trees up to about 15m tall, but which thickens up considerably in zonations to the Pinus-Hylocomium woodland.

The cover and physiognomy of the Juniperus itself here are rather variable. Very widely scattered bushes within a heathy or grassy context would not qualify for inclusion in this woodland type, but many stands have less than 60% cover of juniper and extensive stretches of a closed canopy are rather exceptional: the usual picture is of a patchy cover with some more open areas and others where the bushes form a virtually impenetrable thicket. The individual bushes themselves are also of very diverse form: in some stands, low plants with decumbent branches reaching little more than a metre predominate; in others, pyramidal, conical or narrow, cylindrical forms are in the majority, occasionally attaining 5 m in height.