|Different types of broadleaf tree are
usually fairly distinctive and relatively easy for the layman to identify. In addition,
different species will tend to cast different levels of shade. This in turn affects what
will grow underneath and hence the overall appearance of the wood. Broadleaf
woodlands are therefore most often separated on the basis of the dominant tree species
making up the woodland.
There are two native Oak species which commonly form woodland in
Oak, Quercus petraea, has unstalked flowers and acorns,
but stalked leaves. In contrast, Pedunculate
Oak, Quercus robur, has the opposite characteristics with stalked flowers
and acorns, but unstalked leaves. These two species can interbreed,
forming intermediate forms which may be difficult to differentiate.
Sessile Oak is the dominant Oak on the often shallow, acid soils of
*Highland Britain, whereas Pedunculate Oak is more common on heavy clay soils in Lowland
Britain. (Please note, these terms do not
refer to altitudes, but instead reflect geological trends.) However, it is also common for the species to intermingle both with each
other and with other tree species, to form mixed woods.
||*The dividing line between Highland and Lowland Britain runs
roughly from the mouth of the River Tees in Cleveland, to the mouth of the River Exe in
Devon. Lowland Britain lies to the South and East of this line, Highland to the West.
Oak woods are potentially some of the most diverse
woods in Britain. Oak trees will support an enormous variety of invertebrate life (423
species). Of these, nearly 200 species are butterflies and moths. The rich bounty of
caterpillars and other invertebrates attracts a wide variety of birds. Oaks are also an
extremely long-lived species, with some recorded specimens being as much as 1000 years
old. Such ancient trees have enormous biodiversity value because of the large number of
microhabitats which they provide for species such as lichens (up to 324 species), as well
as a great variety of invertebrates, birds and mammals.
Of the two types, Pedunculate Oak woods are usually more diverse.
They frequently have a very rich field layer, compared to the grassy, or heathy ground
layer common in Sessile Oak woods. Sessile Oak woods often also have a poorly developed
shrub layer, which particularly limits the bird life in the wood.
Beech trees growing
crowded together in a woodland, with their smooth grey trunks and dense, soaring light
green canopies, can create an astonishingly cathedral-like impression. Where they are
close together, the trees are forced to grow tall in the competition for light and will
tend to have tall crowns and few lower branches. In their autumnal finery, beech woods
glow with warm colour as the leaves turn spectacular shades of russet, gold and brown.
trees usually cast a very dense shade. As a result, Beech woods often lack the structure
of more open woods They may have very impoverished field and ground layers because few
plants can tolerate the deep shade. Notable exceptions are Birdsnest Orchids and the
Yellow Birdsnest. Unlike most plants, these species are actually saprophytic. This means
that they feed off rotting vegetation, rather than using light to photosynthesize and
produce their own food. Beech leaves are slow to rot and form humus, so thick layers of
leaf litter often cover the woodland floor.
The distribution of Beech woods is much more
restricted than that of Oak woods. It is a more recent UK species and is still expanding
its range. Beech woods occur mainly on the chalk of the North and South Downs, the
Chilterns, Dorset, Wiltshire, the Wye Valley and the Cotswolds. They tend to be
concentrated on limestone soils although Beech is not restricted to this type of soil.
Thus Beech trees are also found on acid sands and gravels. In some areas, Beech
woods have historically been planted to supply local furniture industries.
Beech woodlands are not as impoverished in terms of
diversity as might be expected from the lack of underlying plant structure. The
Beech trees themselves will support almost 100 different species of invertebrates and over
200 species of lichens. A number of fungi, for example, Porcelain Fungus, are also
associated specifically with Beech woods. Where the trees are separated enough to allow
light to reach the woodland floor, lower plant layers will also develop with a resultant
increase in biodiversity. The harvest of Beech nuts, also known as Beech-mast, produced
every autumn will also attract seasonal additions to the wildlife of the wood. Badgers,
squirrels and a variety of birds, including Nuthatches, will all seek out the nutritious
mast at this time.
introduced Grey Squirrel can play havoc with Beech trees. At certain times of year they
may chew the bark off the tree trunks. In some cases, the damage can be so severe that the
tree is ring-barked and dies as a result. Where this kind of damage is taking place, you
can often see great areas of bark strippings lying underneath the tree. The reason for
this behaviour is debatable. It may be due to territorial behaviour, or possibly because
the animals acquire some nutrients from the bark.
It is not only Beech trees which attract this kind of attention.
Sycamore trees used to be the principle target, but these are not now as widespread as
they once were.