72 Distribution of Chief Forms of Vegetation 



2. Natural and semi-natural grassland covers a very 



large area of the country. The strictly 

 natural grassland, in the sense that it has 

 never been clothed with forest, below the altitudinal 

 forest limit, is probably confined to certain areas of the 

 Chalk, to submaritime pasture derived from salt-marsh, 

 and perhaps to some of the grassy heaths of East Anglia. 

 Above the forest limit and below the arctic-alpine zone it 

 occupies the less poor of the drier soils. The semi-natural 

 grassland is partly derived from woodland by the removal 

 of the trees below the wood-limit on the drier hill slopes, 

 and is continuous with and often indistinguishable from 

 adjacent natural grassland which probably never bore 

 trees. Semi-derelict poor pasture, and permanent pasture 

 which has been " laid down " from arable land and is not 

 manured, may also be considered as semi-natural grass- 

 land, though it has been derived from manured land and 

 not straight from woodland. The pastures, characteristic 

 of many alluvial plains is also at least semi-natural: in 

 some cases such grassland may never have borne trees and 

 so be strictly natural. But the grasslands of the country 

 ■ have as yet been quite insufficiently studied from the 

 standpoint of their vegetation and relationships. 



3. Heathland is developed on the poorer sandy soils, 



„ ^^, o especially in the south-east of England, but 



Heathland. , ■ ■-, c- ^ it 



also on similar areas further north, and on 



well-drained hillsides, over sandstones, etc., poor in nutri- 

 tive salts and in lime. Some of the existing heathland is 

 quite possibly primitive, some is probably derived from 

 woodland by natural causes (see p. 90), but a great deal 

 has certainly been derived from cleared woodland on the 

 poorer soils. 



4. Moorland (on deep peat with low mineral content) 

 j^ is developed in regions of relatively high 



rainfall, such as hill slopes and plateaux in 

 the north and west (upland moor) ; also on the sites of 



