 | |  |
| Deadwood |
There was a time when foresters used to clear away deadwood. Now it is realised that deadwood is vital to the sustained
functioning of woodland and forest. In any woodland, most of the nutrients are locked-up in the vegetation. Trees absorb
nutrients from the soil over many years and incorporate them into their bodies, that doesn't leave much for anything else.
Removing trees from a woodland is a sure way of preventing regeneration - the soil will eventually become too impoverished to
support new tree growth. In redwood and sequoia forests, it is not uncommon for a new tree to grow beside or even on top of a
fallen tree, taking up the nutrients over several years as the dead tree slowly decomposes. Deadwood is also useful to many
other organisms. Decomposers, such as many fungi and woodlice depend upon it (and in turn so do the other creatures that
depend upon the fungi - slugs, insects and the birds that eat the insects) and dead trees, especially if still standing, provide
shelter for animals and birds and insects such as bees which may nest in dead trees. Deadwood really is a vital part of the
ecosystem. Foresters will make deadwood safe - they cut it up into logs to clear paths and cut dead trees down only if they are
unstable and so pose an obvious risk to passers by, but they seldom remove it.
functioning of woodland and forest. In any woodland, most of the nutrients are locked-up in the vegetation. Trees absorb
nutrients from the soil over many years and incorporate them into their bodies, that doesn't leave much for anything else.
Removing trees from a woodland is a sure way of preventing regeneration - the soil will eventually become too impoverished to
support new tree growth. In redwood and sequoia forests, it is not uncommon for a new tree to grow beside or even on top of a
fallen tree, taking up the nutrients over several years as the dead tree slowly decomposes. Deadwood is also useful to many
other organisms. Decomposers, such as many fungi and woodlice depend upon it (and in turn so do the other creatures that
depend upon the fungi - slugs, insects and the birds that eat the insects) and dead trees, especially if still standing, provide
shelter for animals and birds and insects such as bees which may nest in dead trees. Deadwood really is a vital part of the
ecosystem. Foresters will make deadwood safe - they cut it up into logs to clear paths and cut dead trees down only if they are
unstable and so pose an obvious risk to passers by, but they seldom remove it.
A tree does not have to be dead to have deadwood! In addition to the heartwood which no longer conducts sap, trees may
carry dead sapwood where a breach in the bark has exposed part of the tree to infection, or where fire or drought have killed
parts of the tree. Fungi and wood-boring insects will slowly decompose this deadwood. Some of these fungi will only grow on
deadwood and so will not infect living parts, others will spread into the living tree if they can and still others will only feed on
living wood as parasites. A forester will know which fungi threaten living trees and which help them - once the dead wood is
broken down the tree can absorb the nutrients released from it and recycle them. The tree may become hollow as the
heartwood rots away, but this makes the tree lighter and allows the wind to pass through, making the tree generally more able,
not less able, to withstand high winds.
carry dead sapwood where a breach in the bark has exposed part of the tree to infection, or where fire or drought have killed
parts of the tree. Fungi and wood-boring insects will slowly decompose this deadwood. Some of these fungi will only grow on
deadwood and so will not infect living parts, others will spread into the living tree if they can and still others will only feed on
living wood as parasites. A forester will know which fungi threaten living trees and which help them - once the dead wood is
broken down the tree can absorb the nutrients released from it and recycle them. The tree may become hollow as the
heartwood rots away, but this makes the tree lighter and allows the wind to pass through, making the tree generally more able,
not less able, to withstand high winds.
Above: a bracket fungus on deadwood on a living oak tree.
Above, left: a beech log being reclaimed by nature! Centre: fungi on a decomposing
log. Right: more fungi on a tree that still stands. Red liquid full of fungal spores drips
down!
log. Right: more fungi on a tree that still stands. Red liquid full of fungal spores drips
down!
Creepy-crawlies! Above: decomposition is seldom a pretty sight, especially when viewed up-close! In addition to the orange
dots of fungus on the exposed parts of this fallen log, lifting a strip of bark reveals many woodlice, some slugs, a millipede and an
earthworm, all resting and waiting for night-fall to become active. On the right, a large orange slug (about 4 inches or 10 cm long)
has become active on a damp evening as dusk rapidly approaches. This slug was not alone - one was eating a dead earthworm,
another was munching on the leaves of ground-herbs. If you are walking around a wood in late evening, on a damp day, then be
careful where you tread or sit - large slugs are plentiful and emerge under these conditions to forage!
dots of fungus on the exposed parts of this fallen log, lifting a strip of bark reveals many woodlice, some slugs, a millipede and an
earthworm, all resting and waiting for night-fall to become active. On the right, a large orange slug (about 4 inches or 10 cm long)
has become active on a damp evening as dusk rapidly approaches. This slug was not alone - one was eating a dead earthworm,
another was munching on the leaves of ground-herbs. If you are walking around a wood in late evening, on a damp day, then be
careful where you tread or sit - large slugs are plentiful and emerge under these conditions to forage!
The action of the various wood-eating
microorganisms and invertebrate
animals, combined with the effects of
weather (and possibly people passing
by!), will eventually break down any
tree into fragments that join the leaf
litter! The wood of some trees
decomposes quickly, birch wood
decomposes so fast that one has to be
quick to collect a nice birch log before
it's too late. Often the wood rots so fast
that all that remains is the hollow shell
of bark. Other trees take enormous
periods to decompose. Yew wood can
endure for thousands of years before
it finally rots.
microorganisms and invertebrate
animals, combined with the effects of
weather (and possibly people passing
by!), will eventually break down any
tree into fragments that join the leaf
litter! The wood of some trees
decomposes quickly, birch wood
decomposes so fast that one has to be
quick to collect a nice birch log before
it's too late. Often the wood rots so fast
that all that remains is the hollow shell
of bark. Other trees take enormous
periods to decompose. Yew wood can
endure for thousands of years before
it finally rots.
Windfall! Toadstools grow from among the roots of a fallen hawthorn tree. These fungi
are possibly mcorhizal - fungi that normally live fused to the roots of trees in mutual
symbiosis. The tree and the fungus exchange useful materials with one another - the
fungus is get at getting minerals like phosphorus, whilst the tree can make sugars by
photosynthesis. Mycorhizae ('fungus-roots') are essential to the health of trees and few
trees grow well, if at all, without them. Some of these fungi are generalists and are able
to form relationships with a number of tree species, whilst others are specific to one
group of tree species. Importation of foreign trees has caused problems - the trees may
grow only very poorly if the native soil does not carry their own species of mycorhizal
fungus, in which case wood chips of the parent plant species can be used to 'seed' the
soil with the required fungal spores.
are possibly mcorhizal - fungi that normally live fused to the roots of trees in mutual
symbiosis. The tree and the fungus exchange useful materials with one another - the
fungus is get at getting minerals like phosphorus, whilst the tree can make sugars by
photosynthesis. Mycorhizae ('fungus-roots') are essential to the health of trees and few
trees grow well, if at all, without them. Some of these fungi are generalists and are able
to form relationships with a number of tree species, whilst others are specific to one
group of tree species. Importation of foreign trees has caused problems - the trees may
grow only very poorly if the native soil does not carry their own species of mycorhizal
fungus, in which case wood chips of the parent plant species can be used to 'seed' the
soil with the required fungal spores.
Both the fallen hawthorn above and the fallen oak below are still alive because they have at least one major root left in the
soil. If left to their own devices they may continue to grow and put out vertical branches that could become new tree trunks.
The tree below fell after a period of heavy rain and probably the clay soil became waterlogged and semi-liquid, causing the
root disc to swivel until the weight snapped the anchoring roots. Soil failure is a common cause of tree fall, especially when an
area consists of regenerating woodland on soil that was un-wooded for a time. Tree roots may eventually knit the soil together.
The remaining upright stem was grafted on the fallen tree. An earlier fire burnt some of the roots and this may have
contributed to the tree's instability.
soil. If left to their own devices they may continue to grow and put out vertical branches that could become new tree trunks.
The tree below fell after a period of heavy rain and probably the clay soil became waterlogged and semi-liquid, causing the
root disc to swivel until the weight snapped the anchoring roots. Soil failure is a common cause of tree fall, especially when an
area consists of regenerating woodland on soil that was un-wooded for a time. Tree roots may eventually knit the soil together.
The remaining upright stem was grafted on the fallen tree. An earlier fire burnt some of the roots and this may have
contributed to the tree's instability.
This fallen oak was only about 60 years old and its trunk may weigh about 3 tonnes and the crown probably at least the same.
A mature oak could easily weigh ten or twenty times as much. It is just as well, therefore, that older trees are less likely to fall!
A mature oak could easily weigh ten or twenty times as much. It is just as well, therefore, that older trees are less likely to fall!
