11] WOODLAND ASSOCIATIONS 41 
The distinction between the oak and birch woods on the 
one hand and the ash woods on the other hand is very sharp 
and clear in the Peak District, where most of the woods 
may without difficulty be referred to the oak and birch woods 
or to the ash association. It is true that a number of the 
woods are exploited for timber. However, in many of these, no 
re-planting takes place; and the indigenous trees spring up 
again quite spontaneously, either from the cut stools or from 
self-sown seed. In other cases, non-indigenous trees, such as 
beech (*Fagus sylvatica'), sycamore (*Acer Pseudoplatanus), 
larch (* Larix decidua=* L.europaea), and pine (* Pinus sylvestris) 
are planted where the native trees have been felled; but, even 
in these cases, unless the shade cast by the planted species 
differs greatly from that cast by the original ones, the ground 
flora usually affords a fairly conclusive test as to whether or 
not the original wood belonged to the oak and birch woods or 
to the ash wood. A few of the woods of the district may indeed 
be said to be really primitive, as human interference with them 
is confined to the occasional cutting down of one or two trees 
by the occupier of some upland farm. 
Many of the woods, however, are in a degenerate condition ; 
and there is in this district no sharply dividing line between 
degenerate woodland on the one hand and scrub (considered 
in the next chapter) on the other. The questions relating to 
existing plantations and to reafforestation are discussed in the 
last chapter of the book. 
FACTORS RELATED TO THE DISTRIBUTION OF THE 
WooDLAND ASSOCIATIONS 
Sufficient examples of woodland have now been examined in 
this and other districts to enable one to judge, in a general way 
at least, which are the principal ecological factors related to the 
present distribution of the various woodland associations. The 
oak and birch woods of the Pennines, as contrasted with the ash 
woods of the same region, are related to a difference in the 
chemical nature of the soil; for the former woods are here 
strictly confined to non-calcareous soils, and the latter, with 
1 Throughout this book, the species which are not indigenous are preceded 
by an asterisk. 
