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Conference
2006
Plants as infrastructure
Abstract:
Assessment
of Hazardous Trees
ROB
GRAHAM
For many years arborists
have, when assessing hazardous trees, relied on experience, observation,
ingenuity, some commonly held views on species failure patterns,
and a degree of luck. Tree assessment has been an often uneasy alliance
of art and science, limited more by the experience of the assessor
and the weight of their opinion than by data and analysis.
The recent development
of bio-mechanical principles applicable to hazard tree assessment
has set an empirical standard that allows the assessor a degree
of objectivity and scientific analysis.
In the mid 1990s a research
team at Karlsruhe Research Centre, lead by theoretical physicist
and engineer Claus Mattheck, began investigating the bio-mechanical
structure of trees - initially with a view to applying their findings
to engineered structures. The impact of Mattheck's work has had
a radical influence on the understanding and evaluation of trees.
Previously seen as physiological entities, trees have also come
to be viewed as engineered structures - structures that distribute
stress and are subject to external loads in a manner that effects
their design, form and "body language". When these stresses and
loads exceed safety limits this results in fractures and failures.
My paper will briefly
outline the criteria used to assess the safety limits of these loads,
and the analytical processes used to evaluate the degree of hazard
a tree represents. That is; how much decay can your tree have before
it is too much?
Profile: Rob
Graham has spent the last 30 years involved in many aspects of horticulture
and arboriculture. He is currently the principle tutor in the Diploma
in Arboriculture programme at Wintec, where he has been for the
past 10 years. Prior to that he has worked (in descending order)
as an arboricultural consultant, tree company manager, council 'Tree
Officer ', arborist, and general horticultural dogs body. Rob has
worked throughout Europe and Australasia as an arborist, and been
called as an expert witness in numerous court cases regarding the
assessment of hazardous trees.
Rob has a BA (Auckland
University), NDH, CTS (Merrist Wood), and is a qualified teacher.
His obsession is trees.
Email: rob.graham@wintec.ac.nz
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