|
|
|
 |
|
Download the article as an Acrobat pdf - get the
article
here, get Acrobat
here - free |
|
 |
| |
|
|
DECAYING WOOD
RECYCLING WITHIN ARBOREAL ECOSYSTEMS
By Andrew Cowan N.D.Arb. - essentialARB issue
8 spring 2003
Dead wood may well have recently
died, and no longer part of the living tree, or
even attached to it, but we should not be calling
it DEAD, because it’s DECAYING. You may
think this is just another word for the same thing,
but unlike Monty Python’s dead parrot sketch,
the point is that dead wood is anything but dead.
The description dead wood implies a static state,
without the consideration for the process of decay,
and the diversity of life forms involved.
It is the process of decay which
is the focus here, the progression of use by different
organisms. Some like their wood served up fresh
with the sap still ebbing from it’s vessels,
while there are those that prefer it when others
have had their fill and all that is left is a
mass of soft cellulose or brittle lignin. The
diverse array of organisms that are involved in
the breakdown of dead woody tissues is truly amazing.
So much so that decaying wood can be considered
a specialist habitat in it’s own right.
The figures are
quite astounding, just considering the invertebrates
that exist and depend on the decaying wood habitat,
there are includes 1700 species in Britain, 6
% of total British Fauna, but the worrying fact
is that 40 % are either British Red Data Book
Species or labelled nationally scarce. In an effort
to reduce potential losses, the JNCC* and RSPB**
produced a practical handbook called ‘Habitat
Management for Invertebrates’, which was
republished in 2001. |
 |
Ancient
wooded landscape in the Elan Valley Wales.
Photograph by Andrew Cowan 2002 |
|
|
For those of you with a background in woodland management,
Forest Enterprise produced a publication last year,
called ‘Life in the Deadwood – A guide to
managing deadwood in the Forestry Commission forests’.
The cynical among you may think that this is a booklet
on early retirement for foresters, as the Forestry Commission
(FC) undergoes another change of identity, and yes,
the FC is making changes in it’s management strategies,
but they are about new objectives that are evolutionary
rather than revolutionary.
The current emphasis on biodiversity
and protected species, which has come from European
and international agreements and directives, has forced
a change in management strategies and a shift in long
term objectives. However, there is revolution afoot,
with more and more people, and organisations, recognising
the need to focus on a broader picture. In conservation
the world over, the time and money has been invested
in ‘fire fighting’, to protect and preserve
endangered populations of particular species.
The solution is one that manages the system,
rather than concentrating on its component parts, if
we can maintain healthy ecosystems the biodiversity
should take care of itself. However, we cannot and should
not try to force long-term change, if we are to be successful
in sustainable conservation, our role needs to be one
of encouragement and persuasion.
|
| |
|
 |
| Example of a ‘Monolith’
where, due to structural instability the branches
and crown of the tree were removed. The tree
has now been allowed to remain in position
and become decaying wood habitat in a safe
environment Photograph by Mark Robinson 2003. |
|
Historically, woodland
managers have removed dead wood on the basis of
hygiene, to protect the timber resource from what
have traditionally been perceived as pests, like
insects and fungi. This is also true of many,
parkland and garden sites managed by arborists,
where dead wood in trees is seen as a liability,
and is removed for fear it may fall and injure
someone. The result is that there is simply not
enough decaying wood habitat to sustain populations
of many key species of conservation importance.
Dead and dying trees play a vital
role in the functioning and productivity of arboreal
ecosystems through effects on biodiversity, carbon
storage, soil nutrients cycling, energy flows,
hydrological processes and natural regeneration
of trees (Humphrey et al, Life in the Deadwood).
This is a point now generally recognised by most
of us, but this has not always been the case.
The generations of managers that have religiously
felled and removed dead and dying trees, has left
us with a huge shortage, which is likely to take
decades to replace.
The generation gap is aptly demonstrated
when we look at the rare species, which are associated
with our ancient and veteran trees. Many of these
are only found on sites where there has been a
continuity of decaying wood habitat for hundreds
of years. However, ancient trees may appear plentiful
today, but for how much longer? Next time you
visit a site containing ancient trees, look around
at the rest of the wood or parkland, and consider
where the next generation will come from.
The organisms that rely on decaying
wood habitat are becoming increasingly isolated,
in time and place. This is made worse by their
lack of mobility, which means that the creation
of an intermediary ‘bridge habitat’,
is essential if these species are to survive.
This is a fundamental part of our involvement
in the sustainability
of arboreal ecosystems and the maintenance of biodiversity.
|
|
| There are two distinct types of decaying
wood habitat, the first is associated with standing
dead trunks, limbs or branches left around the outside
of the tree, while the second is found within the trunks
and branches themselves, where the decay forms cavities.
It is important to be aware of this distinction because
the habitats that are created are quite different and
require specific techniques to recreate them.
Standing dead wood, whether as whole
trunks or branches within the crown of otherwise healthy
trees, is relatively easy to replace by the resurrection
methods described by Mark Robinson page 6 (see below).
This type of decaying wood habitat breaks down from
the outside in, providing a large surface area for occupation
by invertebrates, fungi, lichens and mosses.
However, when it comes to the creation
of the decaying wood habitat found within the trunks
and branches of trees, the techniques involved are not
quite so simple. The decaying wood inside living trees
decomposes from the inside out, creates cavities, rot
holes and hollow trunks, which are created by invertebrates
and fungi, but go on to provide shelter for a diversity
of birds, small mammals and reptiles.
|
| |
|
| CREATING
THE HABITAT
Training as a practical arborist has progressed
over the years, from the days of old when tree
surgery work involved carting a hand axe and cross
cut saw around the tree, through the era of flush
cutting and cavity excavation, to the enlightenment
of target pruning and an understanding of CODIT
(Compartmentalisation Of Decay In Trees). However,
modern pruning techniques may prolong the safe
useful life of the trees in our parks and gardens,
but they are threatening the sustainability of
arboreal ecosystems, and potentially the life
expectancy of the tree themselves.
There is a tendency to use pruning
techniques, like reduction or thinning, to maintain
trees in a particular form or shape. Our use of
terminology is prone to describing a particular
state, like dead wood for instance, rather than
considering the process of decay, hence decaying
wood. When we look at managing a process, the
emphasis shifts, because this involves an understanding
of how things change as they adapt within a natural
system.
To create the bridge habitat so
desperately needed by some of our rarest flora
and fauna, we are going to have to adopt destructive
pruning techniques, which will contradict
much of our formal training. However, our knowledge
of tree biology is going to be essential, because
if
these methods are going to succeed we need to mimic
the natural processes of tree decline, which
is a slow
progressional balance.
|
 |
This
ancient oak in the Elan Valley, Wales, provides
a decaying wood habitat for numerous organisms.
Photograph by Andrew Cowan 2002 |
|
|
The term veteranisation is being used
to describe destructive pruning methods, which accelerate
the ageing process of trees, by inducing controlled
stress. We do not have the knowledge or understanding
to duplicate nature, because natural tree decline starts
below ground, when the root system becomes exhausted
and can no longer support a full crown of leaves. The
transportation paths then start to break up and the
tree progresses into a stage of retrenchment, like an
army in retreat, resources are moved to a more central
location.
The selective use of destructive pruning
methods that involve natural fracture techniques and
coronet cuts, encourages premature retrenchment, by
reducing the crown area, while providing niche habitat
for decaying wood organisms. This veteranisation of
healthy trees is an essential part of the management
of arboreal ecosystems, particularly in association
with ancient decaying wood habitats where the generation
gap is greatest. It can also be used instead of natural
target pruning when managing hazardous trees, by reducing
the potential for a lever arm to fail, while also retaining
more structure within the trees crown.
SUSTAINABLE CONSERVATION
The creation of bridge habitats is a lengthy process,
so consideration has to be given to the sustainability
of the existing decaying wood, within our ancient arboreal
habitats. As we are all aware the slow process of decay
can significantly reduce the integral strength of trees,
compromising their structural stability, ultimately
leading to partial then total collapse. This is a natural
progression and would not normally be a problem, but
our obsession with the removal of, what has been perceived
as, dead wood now means that for many organisms, there
may be no where else to go.
|
| |
|
|
Research into the sustainable management of ancient
trees has been the focus of the Ancient Tree Forum
for over ten years now. A pruning method known
as restoration pruning became a recognised system
of trying to reinstate lapsed pollards, which
had become unstable. This involved the selective
reduction work necessary to restore a more uniform
and sustainable crown form.
There are some, who would express
reservations about the use of the term restoration
pruning. This is because it is in principle, a
descriptive term for, a method
of restoring, reinstating and imposing a physical state
on the tree, which we perceive to be desirable with
consideration to the management objectives of tree longevity
and safety. However, ideas are evolving and a new term
has been suggested by Paul Muir, of Treework Environmental
Consultancy, that of ‘retrenchment pruning’, where the idea is to mimic the natural processes, encouraging a progression to a more sustainable structural form which considers the tree’s physiological systems. |
|
SUMMARY
The recognition that decaying wood habitat is a dynamic
system of processes, which are a constantly evolving
part of the arboreal ecosystem, is an important step
towards its successful and sustainable management. It
is also a demonstration of how the terms we use can
influence our perception of the management objectives.
Our role as arboricultural managers is one of careful
guidance, to encourage and support natural processes,
not to impose a physical form or state to fit our ideas
of what is right.
We must strengthen our recognition for the fact that
trees live within a different time frame to us mere
humans. Their living processes are almost the ultimate
in sustainability, to a point where, in the right circumstances,
they have the capability to attain immortality. A paper
was recently published in the Arboricultural Journal
(Vol.26 No.3 Sep 2002 pp 213-238) by Neville Fay called
‘Environmental arboriculture, tree ecology and
veteran tree management’, which stresses the management
impacts of tree life spans measured in hundreds of years,
and in some cases millennia. The implications of this
are that the component parts of arboreal ecosystems
can undergo cyclic fluctuations, which are measured
in centuries.
The knowledge we use to develop tree management
strategies, must have a depth of understanding that
considers the tree’s interrelationship with its
environment and other organisms, included within a broad
arboreal ecosystem. It is also essential to have an
appreciation of the ageing process of trees and be aware
that different management methods are needed, which
are sustainable in the context of tree longevity.
CONCLUSION
If sustainable conservation is to work we need to move
away from management strategies that concentrate on
individual species, and embrace an ecosystem based approach.
This is needed, not least, because it would help define
some common objectives for the various wildlife conservation
organisations. As we are now, each group has it’s
own goals and it is common knowledge that these conflict
and are in many cases counterproductive, often cancelling
one another out.
These are not new ideas, and there is
an evolution towards ecosystem based management, with
the consepts of ecosystem health and sustainability
becoming strategic goals. However, it has taken us decades
to get to this stage. |
| |
|
In conclusion it is clear that we need to think
more carefully about the far-reaching effects
and repercussions of our management decisions.
This is hardly a new concept. Aldo Leopold proposed
the following metaphor in an essay he wrote in
1949, called ‘The Land-Health Concept and
Conservation’, which was published for the
first time in a book called ‘For the Health
of the Land’ in 1999.
The biotic clock may continue ticking
if we.
1 - Cease throwing away the parts.
2 - Handle it gently.
3 - Recognise that its importance transcends economics.
4 - Don’t let too many people tinker with
it.
* Joint Nature Conservation Committee
** Royal Society for the Protection of Birds |
|
|
| |
NECTAR SOURCES
A large proportion of the decay process is performed
by juvenile invertebrates, which survive in the shelter
of the decomposing wood, which provides them with all
the nutrients they need to develop. However, when they
leave the decaying wood as adults, they need a source
of nectar to provide them with sufficient energy to
fly, mate and disperse the population to the next available
decaying wood habitat.
The information below has been taken from
a paper, which was published in British Wildlife in
December 1999, called ‘The invertebrates of Britain’s
wood pastures’ written by Keith Alexander. In
this paper Keith Alexander highlights the importance
of decaying wood habitat to a diverse range of rare
invertebrates, and the need to conserve their ancient
habitat.
Nectar provides an energy-rich food, which
can rapidly be assimilated and used to fuel flight,
and pollen is a protein-rich food, which aids egg production.
Flowering trees and shrubs are by far the most important
sources, although other plants can also be very popular,
notably Hogweed Heracleum sphondylium and Wild Angelica
Angelica sylvestris. Hawthorn Crataegus monogyna provides
the classic insect blossom, partly because it flowers
in late spring when so many wood-decay insects are in
the adult stage.
Nectar sources are important throughout
the year, and the presence of the following species
can be particularly beneficial.
• Holly Ilex aquifolium
• Wild Privet Ligustrum vulgare
• Crab Apple Mallus sylvestris
• Wild Pear Pyrus pyraster
• Rowan Sorbus aucuparia
• Bramble Rubusfruticosus
• Guelder-rose Vibernum opulus
|
|
These are just some of the more
obvious species, but even Elder Sambucus nigra,
with its poor reputation amongst entomologists,
can be important for a select few species. For
instance Elder is particularly favoured by the
nationally scarce beetle Aderus oculatus, which
develops in the decaying heart wood of oaks.
HOW MUCH
DECAYING WOOD AND WHERE?
An alliterative phrase adopted and promoted by
Ted Green, is ‘sustainable, successional,
structural, supply of decaying wood’, which
sums it up neatly, but the implications may not
be immediately obvious. However, it is clear that,
an arboreal ecosystem needs just that, if it is
to support a diversity of organisms, and maintain ecological
integrity. It is a description of the level that needs
to be achieved if our creation, management and maintenance
of decaying wood habitat is going to be anywhere near
natural.
|
|
It is however, difficult to accomplish something even
near a natural state, when we have no real idea what
that might be like, since it infers the absence of human
manipulation. We therefore face a challenge where the
ultimate goal is unobtainable, so it is important that
our aims are based on viable benchmarks. This is exactly
what Jill Butler, Fred Currie and Keith Kirby have attempted
to do with a paper called ‘There’s life
in that dead wood – so leave some in your woodland’ published in the Quarterly Journal of Forestry April
2002 (Vol.96 No.2 131-137).
The arboreal ecosystem relies on a sustainable
supply of decaying wood, because the process provides
a range of habitat types, which are utilised by a large
number of different organisms, which are in turn responsible
for a particular stage of decomposition. It is therefore
an absolute necessity that there is enough decaying
wood around to provide the range of conditions needed
to support these organisms.
To achieve a sustainable supply of decaying
wood, with out the necessity to keep importing new material
to a site, we have to encourage a successional ecosystem.
It is fundamental part of managing decaying wood habitat,
that there is the diversity of niches, available at
any one time, to support the full range of organisms
associated with decaying wood.
Finally, we have to appreciate that arboreal
ecosystems have multiple levels, and the creation, management
or maintenance of this habitat needs to work in a structural
way. It is not sufficient to have a sustainable, successional,
supply of decaying wood on the ground, in piles of logs
or brash wood. There needs to be decaying wood in all
of the following places:
|
•
dead limbs on living trees;
• decay columns in trunks and main branches;
• rot holes in standing trees;
• sap runs from decaying cavities or recent
wounds;
• dead bark on standing trees;
• standing dead trees;
• fallen trunks and large branches;
• fallen small branches and twigs;
• dead tree stumps and old coppice stools;
• exposed root plates of wind blown trees;
• decaying wood in water causes;
and it is important to have all
of the above in a diversity of locations, and
conditions, in full sun, dense shade and various
stages in between.
Therefore our management goal is
a Sustainable, Successional, Structural, Supply
of Decaying Wood.
|
 |
A re-erected
Noctule bat roost at Hillingdon Patty Briggs |
|
|
CONSERVING
& CREATING DECAYING WOOD HABITATS
A PRACTICAL GUIDE FOR ARBORISTS
Andrew Cowan’s article above highlights
the important role decaying wood has in providing habitat
for a large variety of species. He discusses how organisations
like the Forestry Commission and the Forestry Stewardship
Council now recognise that there is a lack of decaying
wood habitat within our woodlands which is needed to
sustain many species of conservation importance. He
also suggests that this is mainly due to past arboricultural
and silvicultural practices that focussed on cleaning
out deadwood from woodlands and trees to protect the
timber resource and reduce the potential hazards in
amenity trees. These practices have been driven by the
perception that deadwood in trees is seen as a harbourer
of disease that could result in an increase in an owner’s
liability.
The importance of leaving and making provision
for decaying wood is becoming more widely accepted.
Conservation bodies such as the Ancient Tree Forum,
English Nature and the JNCC have widely publicised the
need to maintain the biodiversity associated with deadwood.
There are an increasing number of arborists realising
the potential in providing decaying wood habitat in
a safe and controlled manner for the benefit of wildlife,
thus providing an additional service to customers. .
Providing this honest and informed service can only
serve to increase public respect, interest and hopefully
job referrals.
COMPENSATION
There have been circumstances in the past couple of
years where developers have been required, as part of
the development plan, to provide decaying wood habitats
as compensation for removal of woodland. The need for
removal of a swathe of Kentish woodland for the new
channel tunnel rail link (CTRL) initiated the translocation
of more than thirty trees to adjacent Woodland Trust
woods. Twelve of these trees were re-erected, while
the remainder were left on the woodland floor as fallen
decaying timber.
|
 |
| During construction of
a dead wood pile for invertebrates as experimented
with and described by Maurice Waterhouse of
the RSPB. Photograph by Mary Robinson 2002 |
|
A mature Oak tree
in Hillingdon, London, was an example where concerns
of the health and structural stability of an Oak
tree resulted in the correct prescription of a
crown reduction. However, the reduction in height
was not straight forward as bats were found in
a large limb. Under the CRoW Act (Conservation
and Rights of Way Act 2000), the limb is considered
a legally protected site for the bats. The branch
contained a Noctule bat roost in an old woodpecker
hole. After consultation with English Nature and
the local bat group it was decided to lower the
limb carefully to the ground as part of the tree
reduction process and then re-attach the limb
to the tree once reduction work had taken place.
This was carried out successfully and as a result
the Noctule bats returned to the roost the following
summer.
METHODS AND
TECHNIQUES
For many years Arborists have been experimenting
with different techniques of preserving and making
decaying wood habitats. ‘Monoliths’,
or should it be ‘Monodendrons’, have
been a simple method of making a dead or dying
tree safe by removing all it’s branches
and reducing its height. However, the habitat
can be improved quite easily by the addition of
boring cuts into the tree to make cavities for
bats, or whole sections of the tree can be hollowed
out to create cavities, without severely reducing
the structural stability of the tree. These techniques
have the added benefit that they promote the decay
process and can provide nest sites for birds. |
|
| Stacks of
logs have been known for a long time to provide a habitat
for a limited range of invertebrates. Maurice Waterhouse,
site manager for the RSPB reserve at Coombes Valley,
has conducted studies of the effectiveness of log piles
at his reserve and has arrived at a design which will
benefit almost all invertebrates associated with decaying
wood. The piles were modified to provide a cavity, enclosed
at either end and on the top. The cavity has been designed
to replicate the conditions that enable the growth of
fungi and promote the decaying process. For those who
are interested in this technique, English Nature has
produced an information sheet in association with the
RSPB called ‘deadwood piles for invertebrate conservation’.
Veteranisation and retrenchment pruning are methods
that are regularly used at Windsor Great Park, as well
as other ancient tree sites, where it is thought necessary
to undertake remedial work on trees that are showing
signs of imminent structural failure and possible premature
death, for example with ancient lapsed pollards or with
large canopied trees with substantial stem defects.
Instead of always target pruning, coronet cuts are sometime
used with the aim of leaving the tree looking as natural
as possible and providing a habitat for decaying wood
organisms. The aim of coronet cutting is to leave a
stump when removing a branch. The stump is then cut
using a chainsaw to resemble a tear or a snapped of
branch as opposed to a pruning cut, trying to mimic
the ‘natural’ results seen following storm
damage. This has the added benefit of stimulating dormant
buds to break, which will generate a new sub canopy
of light harvesting, energy producing leaves.. It can
be very difficult to obtain the desired effect and overall
impression of natural retrenchment, especially for an
arborist who is used to natural target pruning when
undertaking crown reductions.
|
Ring-barking
of trees has also been carried out at various
locations throughout the country, with the intention
of killing the tree to provide standing dead wood.
Whether this actually provides the right type
of decaying wood for invertebrates and other species
is unknown, further studies need to be carried
out on these trees in the future. Initial observation
suggests that the wood becomes seasoned producing
a type of ‘deadwood’ rather than allowing
the varying habitat that comes with the internal
decay process that is produced by fungi. Also
you have to question whether it is necessary to
kill trees to increase the amount of decaying
wood habitat and what will the health and safety
implications be of these trees once the branches
start to fall off.
Another method of promoting decaying
wood habitat is the re-erection of trees, or more
precisely butts and length’s of timber of
trees. This technique has been used with varying
success at various locations around the country.
Roy Finch was one of the earlier pioneers in Gloucester,
where he used a crane to lift long lengths of
timber up against a host tree. The timber was
then secured to the host tree using ratchet straps.
At Roundhay Park in Leeds limbs off a tree were
re-erected when the tree that had been pruned
was found to contain bats. Unfortunately in this
case the bats didn’t return but were replaced
by a family of Starlings. The limb is still in
place today and is providing habitat for certain
deadwood species. |
 |
A recent
attempt of coronet cutting at Windsor during
retrenchment pruning to an Oak tree at Windsor
which was showing signs of severe basal
decay. The use of a large hydraulic man
platform is ideal in these circumstances.
Photograph Mark Robinson 2003. |
|
|
| |
Other methods of re-erecting timber have
included using winches with pulley blocks in the host
tree. The winches could be powered or hand operated
depending on access to the site or, as in the case at
Windsor, where the site is a non-intervention woodland
and the use of heavy plant or machinery is not permitted.
HEALTH AND SAFETY
Most of the methods mentioned above could
have associated hazards both during and after construction.
Health and safety issues associated with trying to promote
decaying wood habitat must be addressed. Initially,
the position in which you intend to create the decaying
wood habitat requires a certain amount of thought. As
with surveying trees the target should be assessed and
the level of risk from the hazard kept to a minimum.
There may be certain areas where, for example, re-erection
methods would not be suitable.
Secondly the method you intend to use
must be planned and in the case of re-erecting, calculations
need to be made before the operation is undertaken to
estimate the correct weights of wood to be lifted and
ropes to be used. Arborists are required, under the
Lifting Operations and Lifting Equipment Regulations
(LOLER), to use equipment with an adequate Safe Working
Load (SWL) and use this correct equipment for the purpose
for which it is intended.
It also states that any anchor point must
be checked and must be capable of safely accommodating
any forces it has placed upon it. In one case a branch
snapped that was used as the anchor for a pulley block
during the erecting of a piece of wood. The branch appeared
on visual inspection to be structurally sound, but internal
decay was present that only became evident after failure.
A method of ensuring an adequate anchor could be to
use the main stem instead of only relying on a branch.
|
 |
| A request from Ted Green
at Windsor, was to move a 4M piece of decayed
Beech containing a rare fungi Hercium erinaceum
hedgehog fungus a distance from where it originally
fell and re-erect it up against another Beech
in an attempt to inoculate the host tree and
continue the existence of the fungus. This
was secured using a wire cable and a nylon
webbing strap around both the tree and the
piece of wood. Photograph Mark Robinson 2002 |
|
RE-INSPECTION
The decaying wood must be put into a regular inspection
cycle once initiated, whether it is a monolith
or a re-erection. Due to the decaying process,
changes in moisture content will cause the wood
to shrink or crack, it could become unstable and
cause a potential hazard. It may be necessary
to reduce the size of the piece of decaying wood
or to re-erect it. Cables, strapping and attachments
should be inspected at regular intervals, as good
guide is found in BS3998: 1989 the British Standard
Recommendations for Tree Work, which recommends
every 3 years for bracing in trees. At Windsor
we inspect our fixings annually.
EXPERIMENTS
Like most experiments conserving and making provision
for decaying wood is a matter of evolution. Whether
all the methods will succeed in their goal will
only be known in the years to come. As Andrew
Cowan mentioned in his article, “it’s
taken years for us to be in the position we are
today, with the lack of decaying wood habitat,
so it will take as long or even longer to return
to a sustainable level.”
Do not shy away from trying something
new, experimenting with different techniques is
essential, but it is also important to learn from
mistakes. For example the method of re-erecting
wood at Ashenbank in Kent was done using large
excavators, this is noticeable on site and makes
you wonder to what extent the ground around the
remaining trees has been compacted and what the
long term effects will be to the remaining trees.
At the same site securing wires are starting to
bite into the host trees and bulldog clips have
come loose. It must be pointed out though that
the work at Ashenbank was not necessarily carried-out
by arborists as it formed part of a large engineering
project. |
|
Merrist
Wood college have undertaken re-erecting experiments
at Windsor and at the college. The majority of these
have been a success and helped in the development of
more recent experiments.
One re-erecting experiment that the college had carried
out resulted in a piece of re-erected wood slipping
from it’s original position which threatens to
tourniquet the host tree or slip out of its securing
cable if it is not rectified. Anyone attempting to use
these techniques should note that the positioning of
the wood against the host tree is of vital importance
to ensure maximum stability, as is the need to support
the piece of wood from falling. Note, it is probably
not a good idea to suspend it in the tree but only to
support it.
WINDSOR GREAT PARK
So far during 20 months working at Windsor
as the chargehand arborist I have re-erected three large
pieces of wood, under the guidance of Ted Green and
Kevin Frediani, and re-secured other pieces of decaying
wood that Ted has done in previous years. All the large
pieces of wood were re-erected using a ‘Tirfor’
hand winch and pulley blocks in the host tree. Different
methods have been used to secure the pieces of wood.
One method we adopted which seemed to
aid the stability of the re-erected wood was to cut
a piece off the base at 45 degrees so the piece of wood
could sit flush with the tree. It was also thought beneficial
to sit the piece of wood on a ring of wood that would
slow down the decaying process and help maintain the
stability of the wood. |
| |
|
We are
presently constructing a deadwood pile, using
the techniques experimented with by Maurice Waterhouse,
so time will tell how successful that is. Also
as part of our on-going tree management system
we regularly make safe our ageing tree stock by
employing the retrenchment pruning technique and
where practicable use coronet cuts as an alternative
to natural target pruning.
Any suggestions or experiences of
any of the above mentioned methods of decaying
wood preservation would be welcome. Contact Mark
Robinson chargehand Arborist Windsor Great Park
robinson_m@lineone.net
Mark Robinson 2003
Mark Robinson has been in the arboricultural
industry for almost ten years. He ran a successful
tree care business based in Scotland for seven
years. He gained the Royal Forestry Society certificate
in arboriculture at the Scottish Agricultural
College, Lanark in 2000. Since June 2001 Mark
has been employed by the Crown Estates at Windsor
Great Park, Berkshire as the charge-hand arborist
where his responsibilities include management
of the Park’s large tree stock, which includes
one of Europe’s largest collection of Ancient
trees. He is continuing his education at Merrist
Wood College where he is about to complete his
Higher National Certificate in Arboriculture.
|
 |
Mark
Robinson winching a section of beech trunk
into position at Windsor Great Park. Photograph
by Kevin Frediani 2001 |
|
|
Mark Robinson 2003
Acknowledgements:
Ted Green MBE, conservationist
Clive Stewart, Woodland Trust, Ashenbank, Kent
Patty Briggs, Herts and Middlesex bat group
Merrist Wood College, Surrey
Andrew Cowan
Mike Ellison
Kevin Frediani & Bill Cathcart – Windsor Great
Park.
|
 |
| Examples of some of the
early re-erections of wood undertaken by Ted
Green at Windsor Great Park, fifteen years
ago. The strapping has been updated recently
by Mark Robinson. |
|
VETERANISATION
Taken from the English Nature publication
‘Veteran Trees, A Guide to risk and Responsibility’
a question asked was, “what is a veteran
tree?” – When a tree trunk is seen
in cross section, a series of concentric rings
are visible, which comprise of annual increments
of new wood. Up to full maturity and under favourable
conditions, the cross sectional area of individual
rings tend to increase year by year; when this
area begins to decrease consistently, the tree
is at the veteran stage. This stage can be the
longest period in the life of some tree species.
A veteran tree is usually old having survived
longer in relation to others of the same species.
During the ageing process and through
the activity of wood digesting organisms, the
tree progressively develops features such as hollowing,
decaying wood and water pools. The tree is gradually
transformed into a complex of habitats with often
unique combinations of niches for many species,
established sometimes over many centuries.The natural tendency to lose branches, to
hollow and decay may initiate an adaptive growth process
in the tree to compensate for potential weaknesses in
the wood strength which may appear as a localised deformation
i.e. a change in the shape of the trunk or branch.
|
|
| |
To provide continuity of specialised saproxylic
habitats found only in veteran trees, the concept ‘Veteranisation’ seeks to replicate over a relatively short period of
time the morphological changes that occur during the
often considerable life of a veteran tree.
|
| back
to top |
| For
more info see:
Articles
Archive
Resources |
|
|
|
|
|
Website
by Digital Detail