82 THE ESSEX NATURALIST.
(2) Wake Arms, and (3) Long Running; a square, with a side of
twenty yards, was corded off and the number of birch trees of
over ten years growth, within the boundary, was counted. At
the first station the average number per square was twenty-
three, at the second thirty-eight, and at Long Running the
number rose to forty. The number of trees per acre calculated
in this manner is for the High Beach station 278.
With the knowledge that we possess of the Forest vegetation
during the four centuries preceding the year 1870 there appears
sufficient warrant for assuming that it represented a high form,
possibly the "climax" of progressive successions, and that
such form has, within quite recent times, undergone a "set-
back," which may have been the result of one or more of the
following causes:—Leaching of the soil, excessive felling, great
fires, permanent lowering of the water-table, or injury caused
by deer and rabbits.
Leaching of the Soil. The analysis necessary to enable
one to judge of the extent to which leaching of the soil has
taken place in this locality has not been completely carried
out. The process of leaching is gradual and continuous, but
at length there comes a time when a scarcity of lime in the surface
soil shows its effect on the vegetation. Here again the change
is in favour of the spread of the birch.
Felling. This has gone on through the centuries; it can
scarcely be claimed to have been much more excessive during
the last 50 years. The timber-right was originally under the
control of the officers of the Crown, but subsequently, having
been vested in many hands, there was little restraint upon those
who appropriated to themselves the most valuable trees that
the Forest supplied.
Fires. These have been periodical at all times. Devastat-
ing fires have taken place within quite recent date, notably the
one in St. Thomas's Quarters (1894), one in the Theydon Quarters,
and the destructive fire north of Great Monk Wood of a few years
ago. The cumulative results of felling and fires have lessened
the rejuvenating power of the Forest, and made it possible
for the birch to increase rapidly.
Water-table. There is historical evidence from ancient
wells that the height of the water-table has varied very little;
data have already been given.