186
THE ESSEX NATURALIST
inhabit the larger, more open, rides and the smaller clearings in the
Forest. On only two occasions has it been found in closed canopy
woodland. The Lizard, on the other hand, we have never seen in such
a situation, although it appears to be far more successful than the
Slow-worm in colonising small open areas in the Forest. It will be interest-
ing to see if the Lizard extends into those areas of former dense wood-
land which have been recently thinned in the Forest, in the same way
as it has colonised the verges of the major roads where the under-
growth had been cut back. It is possible that the Lizard owes its abund-
ance in the Forest district to its ability to populate newly cleared areas
and small open spaces.
The two snakes present in the Forest show a marked dissimilarity in
distribution. The Adder as we have already shown, occurs chiefly in
the northern parts of the Forest, on open plains, and we have suggested
that its distribution may be associated with the presence of gravel
soils. We have never found it in woodland. The Ringed Snake, however,
occurs both on the open plains, and has been seen, although in-
frequently, in woodland with a closed canopy. Possibly there is a cor-
relation between the Ringed Snake's tolerance of differing habitats, and
its wide distribution in the Forest, and the rather specialised habitat
requirements of the Adder, which is apparently distributed only in local
colonies.
It is very difficult to compare the numerical status of the various
species with previous records from the area, as firstly, the concepts of
any two independent observers for degrees of abundance are likely to
diverge widely, and secondly, because it seems that some previous
authors had only a limited knowledge of the area. It seems to us
unlikely that the numbers of the Lizard have changed appreciably with-
in recent times. It is difficult to give any estimate for the Slow-worm due
to the sparsity of reliable evidence, but it does not seem to be so
uncommon as has been claimed. The snakes, however, do seem to reflect
some change in numbers. If Stubbs' observations of the Ringed Snake
at Birch Hall, Theydon Bois, was typical of the whole Forest region
(and there is no reason to doubt this) then it is undoubtedly less common
today. The Adder on the other hand, is more common today than
Stubbs claimed it to be in 1920. However, the situation with regard to
this snake is complicated by a number of interacting factors, many of
which do not seem to affect the other reptiles. Firstly, the dependence
of this species on clearings of moderate size, but with some permanent
cover, limits the likely area of its distribution. These open spaces are
gradually reverting to woodland following the reduction in grazing of
the present century. In addition, the main plant colonisers of these
clearings, seem to be the bracken and the birch, both plants which
produce a dense canopy in a relatively short time, and which thus in
time render an area unsuitable as a habitat. Another factor which we
suggest has a bearing on the numbers of the Adder is the liability of
its usual haunts to fires. Almost every year one or the other of the
areas where the Adder occurs, is burned, or partially burned, and even
if the snakes can escape the heat of the fire, the surrounding cover is