W20 - Salix Lapponum-Luzula Sylvatica Scrub

Summary

Synonymy

Willow scrub Poore & McVean 1957 p.p.; Salix lapponum-Luzula sylvatica nodum McVean & Ratcliffe 1962; Montane willow scrub association McVean 1964; Salix lapponum-Vaccinium myrtillus nodum Huntley 1979.

Constant species

Salix lapponum, Deschampsia cespitosa, D. flexuosa, Luzula sylvatica, Vaccinium myrtillus, Dicranum scoparium, Hylocomium splendens, Rhytidiadelphus loreus.

Rare species

Carex atrata, Polystichum lonchitis, Salix arbuscula, S. lanata, S. lapponum, S. myrsinites, S. reticulata.

Physiognomy

Isolated bushes of Arctic-Alpine and Arctic-Subarctic willows figure occasionally in higher-altitude stands of the moderately calcicolous kinds of ungrazed vegetation included in the Luzula-Vaccinium and Luzula-Geum communities but in some situations these willows are so abundant as to constitute a low bushy canopy to this Salix lapponum-Luzula sylvatica scrub with associated changes in the accompanying flora. Of the various willows represented here, Salix lapponum is the commonest and most widely distributed and usually it dominates, its much-branched bushes forming a patchy cover up to a metre or so high. But it can be accompanied or sometimes replaced by the generally smaller S. myrsinites or by S. lanata, especially prominent in the Clova-Caenlochan area (e.g. Huntley 1979), or S. arbuscula, particularly distinctive around Breadalbane (McVean & Ratcliffe 1962, Ratcliffe 1977). In some sites, too, drawn-up shoots of the normally diminutive S. reticulata make a contribution to the cover and very occasionally the canopy is further enriched by bushes of more widely distributed willows like S. cinerea and S. phylicifolia. Hybrid willows are sometimes found but sexual reproduction even within the rarer species may be very infrequent: in many areas, the number of bushes is small and the sexes often widely separated (McVean 1964a).

There are usually some sub-shrubs growing among the willows. The commonest of these is Vaccinium myrtillus, which can be co-dominant, but V. vitis-idaea, Empetrum nigrum ssp. hermaphroditum and Calluna vulgaris all occur frequently and V. uliginosum occasionally, though generally their cover is low. Often more prominent is a strong contingent of grazing-sensitive herbs, the luxuriant growth of which among the shrubby canopy gives this kind of scrub a very distinctive look.