WOODLANDS 271 



the hazel, sallow-willow, dogwood, and guelder-rose, 

 heath-shrubs taking their place. Characteristic plants 

 are, in addition to those mentioned : HoUy, Scilla nutans, 

 Teucrium Scorodonia, brambles, wUd rose, Potentilla 

 Tormentilla, Rumex Acetosella, Anemone, Digitalis pur- 

 purea, Galium saxatile, Solidago Virgaurea, Hieracium 

 species, the typical heath grass Aira flexuosa, and Holcus 

 mollis. 



II. Oak-Birch-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 (Ehamnus 

 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. Birch- Woo'a.— 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. 



