The Woodlands of England. 
1 35 
sents a stage of its degradation to heath, while some may perhaps 
be in a “ static ” phase, representing a compromise between the 
soil-conditions favourable to the existence of close forest and those 
favourable to the existence of heathland. In any case, it represents 
an extremely well-defined and easily recognisable type of vegetation, 
with constant and characteristic soil-conditions and flora ; and this 
in spite of its locally and widely varying features, consisting here 
of a mixed open wood of oak, birch, beech, and pine, there of pure 
beech high forest, and in other places of pure pinewood or of pure 
heath. 
(C). Birchwood association. In the hilly districts of the 
north of England, the oak (Quercus sessilifora) becomes rare at 
altitudes above 1,000 feet, whereas the birch (Betula tomentosa) 
ascends to 1,500 feet. It seems incontestable that this is due to 
climatic influences, as in all northern countries where the two trees 
occur the birch attains higher altitudes and higher latitudes than 
the oak. If, in the north of England, a well-wooded hill composed 
of non-calcareous rocks is ascended, woods dominated by the oak 
( Q . sessiliflora ) are at first met with ; but, as the altitude increases, 
the oaks gradually diminish in number and size. The diminution 
in number of the oaks is attended by an increase in number of the 
birches; until, at altitudes above 1,000 feet, a wood dominated by 
the latter trees is entered. Along with the oak, most of the other 
trees and shrubs of the oakwoods are left behind when the higher 
altitudes are reached ; and similarly the number of ground species 
becomes much smaller. Since no Alpine and very few sub-Alpine 
species take the place of the lowland species, the floristic features 
separating the birchwoods from the oakwoods of the north of 
England, are largely of a negative character. Ecologically there 
are positive differences, as there is a rearrangement of the dominant 
members of the two associations. They are connected by all 
possible gradations, and the general soil conditions are identical. 
A birchwood in fact is simply a wood in which the oaks, on account 
of the increased exposure consequent on the increased altitude, have 
largely or entirely disappeared, and in which the birches have 
profited by the absence of the competition of the oaks, just as they 
do when the oaks have been extensively cleared in the oak-birch- 
heath association previously described. 
Among the small trees and the shrubs of the birchwoods, the 
mountain ash (Pynis A ucuparia) is often conspicuous; while hawthorn 
