BRITAIN. 



255 



etc. The Quercetum arenosum may similarly yield to scrub and then to grass- 

 heath. Heath (Callunetum arenosum) may arise from oak-birch-heath or it 

 may develop on bare sands. The developmental relations of oakwood, scrub, 

 heath, and grassland are shown in figure 14. 



Formation 

 of sandy and 

 gravelly 

 soils 



Heath 

 Formation 



Dry oakwoorf 

 association 



i 



-> Scrub • 



Grassheath 

 -*■ association 



Oak-birch 

 heath 

 association 



1. Oakwood 



i i"^ 2. Beechwood 



— go 



S-^3. Birchwood 



.2^g'4. Pinewood 



"^ * [sub-spontaneous] 

 5. Heath 



Heath 

 assoc 



atlon 



Scottish 

 'pinewood 



_ Heathy 

 'birchwood 



^k.South English 



pinewood 

 [sub-spontaneous] 



Fig. 14. — Serai relations of woodland in England. After Tansley. 



Moss (137) has indicated the relationship of the formation of siliceous soils 

 as shown in figure 15. 



Woods of Betula tomentosa or of Qnerc os sessiliflora 



^amps 

 Various stages of scrub 



^olinia grassland Nardus grassland with much Calluna 



[Moorland formationj 

 Fig. 15. — Serai sequences in the Pennines, England. After Moss. 



The associations of the chalk subformation are grouped by Tansley and 

 Rankin (178) as in figure 16. 



i^tWOOl 



Beechwood 



[with much yevfl 



iYew wood 

 y 



Chalk scrub + Yew growes 



Chalk grassland »-Chalk heath 



Fig. 16.— Serai commtmities on chalk, southern England. After Tansley and Rankin. 



