CHAPTER II 
WOODLAND ASSOCIATIONS 
Distribution of the woods. Woodland associations of Great Britain. 
Woodland associations of the southern Pennines. Factors related 
to the distribution of the woodland associations. Oak woods of 
Quercus Robur. Transitional woods of Quercus Robur and Q. sessili- 
flora. Oak woods of Quercus sessiliflora ; trees and shrubs ; variation 
of vegetation in the oak woods; influence of shade on the ground 
vegetation. Alder-willow thickets. Birch woods of Betula pubescens ; 
the primitive birch forest. Ash woods of Fraxinus excelsior ; semi- 
natural woods and plantations on the limestone slopes; trees and 
shrubs ; herbaceous vegetation. Comparison of the woodland plants 
of the southern Pennines. 
DISTRIBUTION OF THE Woops 
THE great majority of the woods occur on the slopes of the 
hills, where they ascend, on an average, to about 1000 feet 
(305 m.). Occasionally, they reach an altitude of 1250 feet 
(381 m.). On the Coal-measure rocks, which do not, as a rule, 
reach so high an elevation as the Pendleside, Millstone Grit, 
and Mountain Limestone rocks, the woods occasionally extend 
on to the flatter plateaux. In such situations, woods seldom 
occur at altitudes higher than 800 feet (244 m.). On the whole, 
the woods are of small size; and they by no means cover the 
whole of the hill slopes. In fact, as a rule, the hill-sides are 
occupied by uncultivated grassland (see Chapter IV) or scrub 
(see Chapter III), where they are not cultivated as permanent 
pasture (see Chapter VIII). 
