352 ECOLOGY 



most part different. Species growing mutually together 

 in this way form a complementary society. Reference 

 to the maps (Fig. 223, 1 and 2) will show that these three 

 species do not always grow together. In places you will 

 hnd that one may grow to the exclusion of the others. 

 Under the deep shade of the Beech, the Bracken seldom 

 occurs, but the Soft-grass is frequent, and sometimes the 

 only species is a weak form of Bluebell. The latter also 

 occurs on the stony shallow soil among the Hair- grass. 



Types of British woodlands. There is very little natural 

 woodland in the British Islands. Plantations are numerous, 

 and some of these, being on the sites of native woods, pre- 

 serve many of the features of primitive forest. The wood- 

 lands of Britain may be divided into two main groups, 

 namely : 



(1) Woodlands on siliceous soils : clay, loam, and sand. 



(a) Alder- Willow wood : a lowland type with a ground 

 flora of marsh-plants ; 



(b) Pedunculate Oak wood, with a flowery carpet of 

 moisture-demanding species ; 



(c) Sessile Oak wood, on drier, often sandy, soil : a type 

 of which has been given above (Fig. 223) ; 



(d) Oak-Birch-Heath wood, with a ground flora of 

 heath-plants ; 



(e) Birch wood : characteristic of the northern up- 

 lands, in which the Birch is the dominant tree ; 



(/) Pine wood : this type differs from the above de- 

 ciduous woodlands in being composed mainly of 

 evergreen coniferous trees. 

 Native Pine woods occur in Scotland, and were formerly 

 extensive in England. The ground flora is usually of the 

 heath type ; and seedlings of the native Scots Pine often 

 develop freely on heather moors, both lowland and upland, 

 and form a Pine-Heath wood. Many of the present Pine 

 woods are plantations, and exotic conifers are commonly 



