can be thought of as being a bit like nesting Russian Dolls. If we take rotting wood as an
example of a particular microhabitat within a woodland, this could be further subdivided
down into ever smaller microhabitats. For example, different, smaller microhabitats within
the overall rotting wood microhabitat, would be created by such variable factors as:
- The species of tree which the rotting wood was
- The length of time it had been rotting.
- Whether it was in sunshade or shade.
- Whether it was still standing or had fallen.
- Whether it was in a log pile or on its own.
- The type of organisms previously, or currently in
residence. These might provide food opportunities, or old abandoned mines and galleries
which could be used by other, later colonizers.
All of these factors will subtly alter the
environmental conditions present in individual pieces of rotting wood and hence also the
specific species of fungi, bacteria, plants and animals to be found there.
||This enormous variety of rotting wood microhabitats
means that in Britain, rotting wood alone may play host to over 1700 different
invertebrate species, before you even begin to count the other species present.
Larvae of the Sabre Wasp (left) are
some of the many inhabitants of rotting wood.
If we continue the scaling down process even further,
hundreds of different species of fungi will inhabit rotting wood in woodlands, many of
them specific to the wood of particular tree species. Those species of fungi which produce
larger fruiting bodies*, provide microhabitats in their own right for over 200 species of
flies, beetles and small moths. Many of these live inside the fruiting bodies in their
larval stages. Each of these invertebrate species will have their own subtle requirements
and some may be found only in the fruiting bodies of one particular species of fungus - a
very specific microhabitat indeed!
(*A fruiting body, such as a mushroom, is the reproductive
structure which is normally the only part of the fungus which we see.)
A single mature living tree within a woodland will
provide another staggering range of microhabitats. These range from the leaves, flowers
and fruits of the tree (different microhabitats, available at different times of year),
through to the lichens and mosses growing on the bark of its trunk and branches. Different
lichens will colonize different areas of the tree depending on the age of the bark, its
position, how much shelter is available and how old the tree is. The lichens themselves
will provide shelter and food for a variety of animals, as will the mosses and algae also
growing on the tree's trunk. A variety of millipedes, woodlice and caterpillars can be
found grazing on the different plants colonizing the tree's surface, all of them
attracting their own predators. Viewed under a microscope, ,just one small piece of moss
taken from a tree trunk, will offer up a normally completely unseen world, heaving with
||Fissures in the tree bark
will harbour a range of small invertebrates, depending on how gnarled and old the bark is
and hence, how deep the fissures are. Knot holes may develop in the trunks of older trees.
These will provide nesting sites for birds, such as woodpeckers and Nuthatches, as well as
bats, ants and wasps. Many of these nests have their own characteristic communities of
tiny animals associated with them, some of them very specific and occurring nowhere else.
Depressions or holes within the main body of the tree
may hold rain water, which again will contain their own characteristic communities of
aquatic invertebrates. Sapflows from injuries to the tree are an important source of food
for moths and butterflies. Beetles, mites and fly larvae will feed on the yeasts and other
micro-organisms also capitalizing on the sap flow. The list of potential microhabitats is
Rotting wood and a single tree are just two examples
of larger microhabitats which can be endlessly scaled down into ever smaller
microhabitats. The greater the structural diversity within a woodland, the more of these
types of microhabitats there will be available.
- Structural diversity is enhanced through having a variety of
different tree species, of differing ages, making up the woodland.
- Natural environmental variations within the woodland, such as areas
of differing soil type (for example, acidic, or lime) and degree of water saturation, will
provide conditions suitable for the growth of a wide range of different types of plants.
- Glades and rides within the wood, provide areas suitable for less
All of the variety of plants within a wood will offer different
microhabitats and food opportunities for an enormous number of other organisms.
The decaying products of all these plants, from leaf litter to
rotting wood, provide food sources and microhabitats for thousands of other different
kinds of organisms. Large individual rotting logs, piles of logs and old tree stumps
provide a staggering number of microhabitats, as will old trees. If these are left to die
naturally in the woodland, rather than being harvested at an appropriate time, they will
acquire a value for wildlife which is usually proportionate to their age.
Continue to Tree