PLANTING OF WATER CATCHMENT AREAS 109 



The moorland zone, occurring on the hills and mountains 

 above the limits of the hill pasture, owes the peculiar 

 character of its vegetation to the presence of peat, which 

 varies in depth from a few inches to many feet, and overlies 

 shale, sandstone, granite, and other rocks, but is rare on 

 limestone. The peat also varies much in the quantity of 

 water which it contains, and to this is due the various types 

 of vegetation that are met with in the moorland zone. 

 Botanists distinguish in this zone, as main types or associa- 

 tions, heather moor, cotton-grass moor, Scirpus or spike-rush 

 moor, bilberry moor, and Sphagnum moor. 



Heather grows on peat where the drainage is good, and 

 is most vigorous when the water content of the peat is less 

 than 50 per cent. It thus occupies the slopes of the hills 

 and mountains immediately above the hill pasture, and 

 ceases to thrive on the higher parts, where the ground is 

 flatter and the drainage is impeded. There are thus, as a rule, 

 extensive heather moors on the slopes with shallow and 

 dry peat, succeeded above by cotton-grass, Scirpus, and 

 Sphagnum moors, where the peat is deep and sodden with 

 moisture. 



The lower limit of the heather moor is determined by 

 the cessation of the peat and is very variable. It occasion- 

 ally descends in the Southern Pennines to 750 feet, but as 

 a rule in this range seldom goes lower than 1000 feet 

 elevation. Its upper limit is mainly a question of drainage 

 and scarcely depends on altitude, as heather grows to a high 

 elevation if the peat is dry. In the Southern Pennines the 

 heather moor ascends to about 1500 feet, but it often gets 

 up to 2000 feet in the Northern Pennines. The heather 

 moors are the typical grouse moors, and are often preserved 

 for shooting, the heather being set fire to every few years to 

 promote young growth. 



The heaths in the south of England, which are often 

 immense tracts at a low elevation, are also covered with 

 heather, but are distinct from the heather moors in the 

 nature of the soil. The soil of the moors is always peat, 

 whereas that of the heaths is poor sand or gravel, the upper 



