11] WOODLAND ASSOCIATIONS 59 
primaeval oak (Quercus sessiliflora) forest. On the accompanying 
vegetation maps, they are given the same colour as the oak 
woods of which they originally formed a part. 
Most of the alder-willow thickets occur on the Pendleside 
shales; and on these soils at the lower altitudes, woods are 
now rare. It seems highly probable that this is due to the 
fact that the shales make excellent agricultural land; and the 
original woods on the shales, therefore, have nearly all been 
felled, and the land put down to cultivation, chiefly as permanent 
pasture (see Chapter VIII). 
The flora of the alder-willow thickets does not differ 
materially from that of the damper parts of the oak woods. 
Occurring in the cultivated area, it is natural to find in them 
some alien trees, and some invading pasture species among the 
ground flora. The following trees and shrubs were noted in 
the ash-alder thickets near Edale and Castleton :— 
Subdominant species 
Salix fragilis Alnus glutinosa 
S. cinerea Fraxinus excelsior 
Locally abundant species 
Salix caprea Rubus spp. 
Corylus Avellana Rosa tomentosa (rare) 
Betula pubescens R. canina 
Ulmus glabra Pyrus Aucuparia 
(=U. montana) Hedera Helix 
Prunus spinosa Lonicera Periclymenum 
Occasional and rare species 
*Larix decidua Q. sessiliflora 
*Populus canadensis *Prunus insititia 
*Castanea sativa Rosa arvensis 
*Quercus Robur *Acer Pseudoplatanus 
Brrcow Woops or BETULA PUBESCENS 
Birch woods were recognized in Scotland by Robert Smith 
(1900, a and 6) who stated that they were quite natural and 
self-sown. Smith did not state which of the two British species 
form the dominant element; but both are actually abundant 
— 
