69 
BIRCH GROVES OF EPPING FOREST. 
Being a Presidential Address delivered to the Club at the Annual 
Meeting on 25 th March , 1922. 
By ROBERT PAULSON, F.L.S., F.R.M.S. 
(With 3 Plates and 1 Text Diagram.) 
T HE naturalist who has, through a period of several years, 
taken a keen interest in Epping Forest, or in other wood¬ 
land of considerable area, especially if it be on gravel or sandy 
soil, will have become more and more conscious of a change 
gradually manifesting itself in certain features of the locality 
on which he was particularly concentrating his observation. 
Probably he will have become aware of an increase, or decrease, 
in numbers of some mammal, bird, insect, tree or ground plant. 
The vegetation of woodland may be rendered unstable by 
occurrences such as (1) fires, (2) extensive felling (especially 
when it is not followed by subsequent replanting of the same 
species of tree as that cut down), (3) by a lowering of the water 
table on the introduction of artificial drainage, or (4) unstability 
may be the natural result of the leaching (washing out) of mineral 
matter that is rendered soluble in the soil by rain-water charged 
with carbon di-oxide, which is given off in large quantities from 
the acid humus that frequently covers the surface of the ground. 
The subject of variation in the vegetation unit of woodlands 
was suggested to me by a striking example that has recently 
declared itself in an unmistakeable manner in certain parts of 
Epping Forest, especially on the lighter soil of the more elevated 
situations. There has, within the past fifty years, been a great 
increase in the number of birch trees ; where there were tens 
there are now thousands. No detailed suggestions as to the 
probable cause or causes for the remarkable increase in this 
locality have yet, so far as I am aware, been made. A similar 
increase is taking place elsewhere in the south-eastern counties, 
as at Chiselhurst (Kent), Wimbledon Common and Oxshott 
Common (Surrey), Oxhey Wood (Hertfordshire), and Ruislip 
Woods (Middlesex), but as to the extent to which this is happen¬ 
ing, there are not sufficient data to enable one to compare these 
localities with Epping Forest. At Oxshott it is quite evident 
to the casual observer that the invasion of birch and pine is very 
