Article - LOOKING INSIDE YOUR ASSET
Decay in wood is a natural recycling process, however it is a constant
problem to the Arborist who has to determine the extent of decay, as
in most cases decay is not visual to the human eye. To aid the Arborist
and Tree Managers of Australia ENSPEC Pty Ltd have commenced scientific
measurements with a Sonic Tomograph.
The Picus Sonic Tomograph is a new
precise measuring tool that detects and electronically measures the
amount of decay in it's various stages. The Sonic Tomograph obtains
data in a non-invasive or destructive manner, and produces detailed
information in a computerised form.
The purpose behind ENSPEC Pty introducing the Picus
system was to enable ENSPEC to provide a service throughout Australasia
that conclusively provides undisputable evidence of the extent and spread
of decay in trees and provides the first accurate measurement tool for
correct Risk Management of Trees.
After many field trials and large consulting projects
ENSPEC was concerned that the Diagnostic Drill being used was providing
measurements that were inconclusive, inconsistent and open for interpretation
by the arborist when analysing the extent of decay in trees.
Part of the inconsistent interpretation is due
to all current published documentation and research being based on European
trees, these tree species are consistently softer in their timber strength
than our native species.
The results that were being produced by the diagnostic
drill varied. This inconsistency dramatically increased when drilling
indigenous trees due to the strength and durability of the timber, both
live and dead.
Due to the wood strength of many indigenous species
the diagnostic drill does not have the ability to enter the hard/sound
wood. ENSPEC has also experienced this with some introduced species
that have acclimatised to Australia's harsh topography.
ENSPEC's other main concern associated with the
Diagnostic Drill is the destructive way that the tests are performed.
The probe of the Diagnostic Drill is known to provide decay and pathogens
with a way to overcome the trees internal defence mechanisms by breaking
through defence walls and creating 'pathogen highways' into previously
uninfected parts of the tree. So when the drill of the probe is extracted
through uninfected parts of the trees internal system it aids the spread
of the pathogens, hence affecting more area of the trees sound wood.
Displayed in the photo below is scientific research
evidence that now proves that wood-decaying pathogens can move through
the test holes.
The picture above (white arrow) displays a penetration hole of the Reaction
Zone with the "Diagnostic Drill" enhanced fungal colonisation
of the sapwood by Ganoderma applanatum.. The picture left (black arrows)
provides evidence of the ability for fungus to overcome the reaction
zone and subsequent degradation of the adjacent sapwood. (copyright
to and provided by David Fener 2002)
The Picus system totally overcomes this problem,
as it is a non-invasive method of inspecting the internal parts of the
tree. The sonic waves sent through sensors are placed on the outer part
of the tree just below bark. All parts of the equipment that actually
touch the cambium layer can be cleaned or replaced for each individual
tree inspection.
HOW THE PICUS SYSTEM WORKS
The Picus system utilises sonic waves generated
through sensors placed around the outer circumference of the trunk or
branch to gather specific measurements of the internal parts of the
tree. This data is then analysed by the Picus software, which accurately
electronically maps the internal wood densities of the tree being tested.
The theory of the Picus is based on the principal that sound waves conduct
better through sound wood than decayed wood.
The result of the sonic waves produce a 2 dimensional
computer generated picture that accurately represents the shape of the
tree and interprets via different colour coding the occurrence and level
of decay existing within the tree.
The Picus system can currently use up to 22 individual
sensors spaced apart allowing for a trunk circumference of 22 metres
to be measured
Location of the Picus sensors is determined by
performance of a detailed visual tree assessment that identifies areas
for concern or potential problems. This is a critical part of the testing
process and should be carried out by skilled Arboricultural personnel
certified in tree assessment.
Placing the Picus sensors in the correct location
is essential to provide an accurate picture of the overall shape of
the tree. This is achieved by placing the sensors on natural ridges
and depressions to allow inclusion of all the circumference of the tree,
which in turn provides an accurate overall picture.
The Picus has been trialed extensively since its
arrival in Australia. The trials were performed under the expert instruction
and supervision of David Ferner a Mycologist from the University of
Frieburg, Germany.
The results to date have proven
that 85% of trees being removed because they were condemned under VTA
could have been retained and risk managed for many years to come.
The photograph above shows damage to the base of
an Oak tree. The roots system was damaged when the pavement was upgraded.
Concerns were raised over the extent of decay as two arborist reports
had varying information and outcomes. The Picus provides clear evidence
that the decay is restricted to a very minor area of the tree base.
The percentage of green area in the results is altered wood but is classified
as solid wood for diagnostic purposes. In the case above the Oak tree
has 92% solid wood, 6% altered wood (greenwood) and 2% decay.
Conversely the reverse is true
The tree pictured above had been recently inspected
and assessed to be healthy and sound, the Picus test undertaken on this
tree showed that the tree has a pocket of decay at ground level The
blue/white section of the tree is hollow, the purple section an advanced
state of decay with the green being modified or altered wood. The tree
was initially tested due to failure of other trees in the area and a
visual tree assessment would not have identified any internal problems.
The red ring indicates the 30% sound wood area.
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The images to the left show a beech tree
that has been tested and dissected. It clearly defines a bifurcation
in the tree and provides evidence that the tree has been able
to produce strong defence walls to try and hold the decay within
itself.
The walls are clearly visible in MP 2, 8, 10 & 12
ENSPEC Pty Ltd is fully committed to further
research and development of the Sonic Tomograph and to that end
has developed a close working relationship and alliance with Dr.
Francis Schwartze and David Ferner (Frieburg University) to ensure
future exchange of information on the developments made with the
Picus Sonic Tomograph.
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In the coming months/years ENSPEC will continue
their scientific research to establish;
v Preservation of trees
v Risk Management Strategies
v Understand Rates of decay
v Percentage of Sound wood required to structurally support a tree
v Method of containing decay once located in a tree
ENSPEC will have the Picus Sonic Tomograph and
other measuring equipment on display at the ISAAC 2003 National Conference
in Adelaide; further results will be available for viewing.
ENSPEC Pty Ltd in conjunction with Dr Francis Schwartze
and David Ferner would like to thank the following councils for their
co-operation and use of trees for scientific research. In no given order
- South Australia - City of Salisbury, City of Mitcham, City of Whyalla,
City of Mount Gambier, Victoria - City of Moreland, City of Boroondara,
City of Darebin and Frankston City Council.
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