ZOOM | Fall/Winter 2019

“A hazard situation requires the presence of both a tree with the potential
to fail and a target,” say Nelda Matheny and James Clark in their book
A Photographic Guide to the Evaluation of Hazard Trees in Urban Areas,
published by the International Society of Arboriculture.
Given that the target is your house, how do you determine if the tree
within falling distance has the potential to fail?
First consider the species of the tree. Each has different growing
characteristics, which impact on their strengths or weaknesses. From
Gibsons to Pender Harbour, cedar, hemlock, and Douglas fir share air
with the red alder and big leaf maple. Each varies in its resistance to
decay. Hemlock is shallow-rooted, subject to root rot and internal decay.
The shallow roots and bent tip profile contribute, in high winds, to being
literally twisted out of the ground. It is probably the least stable of the
evergreens.
The Western red cedar, on the other hand, seldom fails on its own.
Although branch failure is rare even under heavy snow loads, human
interventions cause its demise. Mutilation of the crown (the infamous
practice of topping) exposes the tree to decay. When the leader
re-grows, it creates a sail at the top of the tree that makes it more
susceptible to blowdown.
Age, size of the tree, and the environment in which it resides are
three factors to consider when trying to estimate the danger of a tree
going over. What kind of damage has occurred to the tree in the past,
particularly to the roots? With these giants, close to forty percent of the
total mass of the tree is below ground level; the roots may extend from
the drip line sixty, seventy, eighty feet.
The tall-growing Douglas fir (to 90 m) is the most prolific in British
Columbia. In high winds, heavy branches snap off easily. Trunk failure
can be caused by co-dominant stems with included bark, resulting in
internal decay, fungopathogens, and root rot.
Construction, which now surrounds us all, will take down any of these
large trees. With the use of heavy machinery, roots are compacted and
often severed. Use of fill for landscaping and septic fields can raise soil
level around the tree, depriving the roots of oxygen.
Here is a checklist of “severe” failure indicators: visibly unstable,
mainstem cracked, severe decay, broken stem or branch, severe lean,
ground cracks or heaves, dead tree, and a hanger (a broken-out top
which is caught in the tree).
Look for these symptoms of instability: “coning up” (where the tree has
an excessive number of cones), conks and fungal bodies growing on the
wood, “included” bark, co-dominant stems, crown decline and multiple
tops, wounds and decays, excessive end weight, multiple attachments,
exposed or damaged roots, deadwood, and crown dieback.
CASEY HORNER PHOTO
We are the trees, ancient witnesses. After so much time, we are still so happy
to hear familiar sounds as squirrels, raccoons, coyotes, bears, and deer scurry
under our canopy. Birds still open their throats to the sky, urgently crying for
their breakfast, in the way they have, spring after spring for millennia. We are
the trees. We are alive and we celebrate the good fortune of every second of our
continuing existence.
VISION WEBAGENCY PHOTO
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