98 Suggestions for Beginning Survey Work. 
limited units. Simplicity will be attained if the attention is at first 
restricted to some one common type of vegetation ; the oak-wood 
so general throughout Britain will serve as an example. 
Formations. A natural wood consisting entirely of oak trees 
has one dominant form—the oak—whose presence is determined by 
the prevalent climatic, soil, and other conditions, while its size and 
gregarious nature give it dominance; in this wood there may he 
other sub-dominant trees or shrubs ( e.g ., birch or hazel), more or 
less isolated, but which, given the opportunity by removal of the 
oak, will become dominant forms; the motley carpet of the oak- 
wood is made up of many species dependent on the larger forms 
for shelter and shade, or living as epiphytes, parasites, and humus 
saprophytes, and including not only flowering plants, but ferns, 
mosses, lichens, and fungi. The vegetation of the oak-wood is thus 
a mixed community with complex relationships, its members 
struggling for existence and dominance, but it is a coherent whole 
and may be studied as a unit or Formation. The oak-woods of the 
present day are small and detached, but they are certainly the 
remains of an extensive oak forest which extended far and wide 
before it was cleared to make way for farm-land. 
Other well-marked standard formations' are: — 
Group I. Deciduous woods, e.g. Beech wood (native only in 
the South of England). 
Group II. Coniferous woods, e.g. Scots Pine. 
Group III. Xerophilous herbaceous and undershrub vegeta¬ 
tion (including moorland): (a) Heather moor, where Ling [Calluna) 
is strongly represented. ( b) Cotton-Grass Moor or Moss ( Frio - 
phorum vaginatum, etc.). ( c) Grass-land, where grasses prevail, 
e.g. on the Chalk Downs and Mountain Limestone. ( d ) Grass- 
heath, where dominant grasses (e.g. Nardus stricta) are mingled 
with sub-dominant heath plants (e.g. Calluna, Erica spp., Vaccinium 
spp., etc.). 
Group IV. Maritime: (a) Sand-Dunes. ( b) Salt Marshes. 
(c) Shingle Beaches. ( d) Sea Cliffs. 
Each of these formations has a distinct appearance, due to one 
or more plants which dominate it. The presence of the dominant 
plant is determined by combined climatic and edaphic (soil) condi¬ 
tions, and in most countries man as tiller of the soil, as grazier, or as 
game-preserver has left his mark on the natural formations, or has 
displaced them by “ substituted formations.” 
Associations. Within the limits of a formation, there exist 
smaller societies, each one with dominant, sub-dominant and depen¬ 
dent species of its own. Thus the undergrowth of an oak-wood 
may consist of a Pteris-Scilla-Holcus association, in which Bracken, 
Bluebell and Yorkshire Fog together cover a large area; again it 
may be a Calluna- Vaccinium association, or one of several others. 
Each association is determined by a set of factors, as a rule edaphic 
factors. 
Work on vegetation may be concerned with the distribution of 
formations, or it may be a record of the associations of a smaller 
area. It may be a study of the conditions which determine the 
existence of a single formation or of an association. It is not easy to 
say with which of these it is best to begin ; everything depends on the 
1 This list is by no means exhaustive of British plant-formations. 
