With something as complex and variable as vegetation, no key can pretend to offer an infallible short cut to diagnosis. The following should therefore be seen as simply a crude guide to identifying the types of woodland and scrub in the scheme and must always be used in conjunction with the data tables and community descriptions. It relies on floristic (and, to a lesser extent, physiognomic) features of the vegetation and demands a knowledge of the British vascular flora and, at certain points, of some bryophytes. It does not make primary use of any habitat features, though these can provide a valuable confirmation of a diagnosis.

Because the major distinctions between the vegetation types in the classification are based on inter-stand frequency, the key works best when sufficient samples of similar composition are available to construct a constancy table. It is the frequency values in this (and, to a lesser extent, the ranges of abundance) which are then subject to interrogation with the key. Most of the questions are dichotomous and notes are provided at particularly difficult points and where confusing zonations are likely to be found.

As in the construction of the scheme, samples should be of 50 x 50 m for woodland canopy and shrub layer or sparse scrub, 10 x 10 m for dense scrub canopy, with either 4 x 4 m or 10 x 10 m for the field and ground layer.

1 Low scrub dominated by Salix lapponum, sometimes with S. lanata, S. myrsinites or 5. reticulata, with luxuriant mixtures of Vaccinium myrtillus, V. vitis-idaea and Empetrum nigrum ssp. hermaphroditum, Luzula sylvatica, Deschampsia cespitosa, tall dicotyledons and bryophytes; a rare community of montane crags and ledges

Scrub or underscrub with one or more of Crataegus monogyna, Prunus spinosa, Sambucus nigra, Ulex europaeus, Cytisus scoparius, Rosa canina agg. and Rubus fruticosus agg. frequent and often abundant; saplings of taller trees sometimes numerous but never forming an overtopping canopy 57

High forest or coppice in which Crataegus monogyna, Prunus spinosa, Sambucus nigra, Rosa canina agg. and Rubus fruticosus agg.