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THE ESSEX NATURALIST
Fig. 2.—Block diagram to show topography of the survey area. The
boundaries of vegetation zones are shown.
The underlying rock is London Clay, and away from the wood-
land the surface has the characteristics of clay pasture with only a
very shallow topsoil and humus. As the grassland merges with
woodland, the topsoil becomes deeper, with a layer of decomposing
leaves and humus.
The area possesses a number of vegetation zones, which are
distinguished in Figure 1. A brief description of each follows.
Zone 1. An area dominated by dry scrub oak, which is grow-
ing into dense thicket. In the winter and spring, before the trees
are in leaf, plenty of light penetrates through the canopy, allowing
a growth of brambles and heath grasses, of which Agrostis tenuis
and Holcus mollis are the most abundant and tend to dominate
the field layer. However, where the trees are larger, and the
canopy more dense, the ground layer has disappeared and the
floor is carpeted with oak leaves. Adders are found here in spring
and autumn, but rarely in summer.
Zone 2. This area is dominated by bracken, which produces
dense shade in summer. Some bramble, scattered oak and birch
saplings are present. There is little or no grass present, and
adders are seen here only exceptionally.
Zone 3. This is essentially rough pasture, which, with the
cessation of grazing, has become a rank, tussocky grassland, with
expanding clumps of hawthorns. These bushes, briars, crabapples
and brambles are invading the grassland, and amongst the shrubs
many young oaks have sprung up and survived to saplings. The
zone is typical of pasture on London clay left to revert to wood-
land scrub. Adders are found here mostly in the summer months,
rarely in spring and autumn.
Zone 4. An area dominated by close standing elm saplings,
inter-spaced with well grown hawthorn. The lower shrub layer is
composed of nettles and bramble in dense stands. Adders are found
here in late spring and autumn, along the north-western edge.
Zone 5. This zone is similar vegetationally to zone 3, and
differs from it only in aspect, being level and at the crown of the
hill. Female adders have been found here in summer.