69
BIRCH GROVES OF EPPING FOREST.
Being a Presidential Address delivered to the Club at the Annual
Meeting on 25th March, 1922.
By ROBERT PAULSON, F.L.S., F.R.M.S.
(With 3 Plates and 1 Text Diagram.)
THE 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