WOODLANDS 271 
the hazel, sallow-willow, dogwood, and guelder-rose, 
heath-shrubs taking their place. Characteristic plants 
are, in addition to those mentioned: Holly, Scilla nutans, 
Teucrium Scorodonia, brambles, wild rose, Potentilla 
Tormentilla, Rumex Acetosella, Anemone, Digitalis pur- 
purea, Galium saxatile, Solidago Virgaurea, Hieracium 
species, the typical heath grass Azra flexuosa, and Holcus 
mollis. 
II. Oak-Birech-Heath Association.— On dry, coarse, 
sandy soils or dry peaty soils in the lowlands, the birch 
and heath-plants which we found were present in the 
dry oak-wood become so numerous as to constitute a 
distinct association. This type is common round London 
on the dry heaths and commons—e.g., Bostall Heath and 
Keston Common. Silver birches are abundant, but the 
woods are very open, long stretches of ground being 
covered with grass (Aira flexuosa chiefly) or shrubs (ling, 
gorse, whortleberry, honeysuckle, and bramble). The 
characteristic shrubs and small trees are holly, mountain- 
ash, hawthorn, blackthorn, alder-buckthorn (Rhamnus 
Frangula), juniper, and white beam. Herbs characteristic 
of dry ground are common—e.g., Teucrium Scorodonia, 
Galium saxatile, and Potentilla Tormentilla. 
This association is generally regarded as a stage in the 
degeneration of oak-wood into heath, brought about by 
a gradual increase in the dryness of the soil. The next 
stage in its deterioration is seen in the rough common 
dominated by bracken, gorse, and bramble, described in 
Chapter XXX. 
III. Birech-Wood.—At high altitudes (above 1,000 feet) 
the dry oak-wood changes into a birch-wood, and there 
‘seems no doubt that the change is due entirely to climatic 
conditions. The oak cannot grow at these high levels, 
and the birch, freed from competition, becomes the 
dominant tree. The undergrowth is much the same as 
in the oak-birch-heath association, but mosses are very 
abundant. In the north of England, and more especially 
in Scotland, many of the plants characteristic of pine- 
woods (p. 274) are found in the birch-wood. 
