The letter West Van’s Tree Bylaw: Let Common Sense Prevail, Jan. 8 Mailbox has some inaccuracies which should be pointed out.
The term “overgrown tree” used in the Jan. 8 article implies the tree has outlived its usefulness. Quite the contrary; in addition to their esthetic value, old trees have ecological value.
Perhaps the most important ecological roles they play as far as our area is concerned are as perch and nesting trees for the bald eagle whose prime feeding habitat extends along the entire shoreline of the highly productive Burrard Inlet and its estuaries. Fortunately the lower elevation residentially developed areas of West Vancouver have the highest concentration of old trees along the shores of Burrard Inlet, allowing the bald eagle to use these old trees for nesting and what is called perch hunting.
Because the nests become so large and heavy, they require strong branches to construct the nest. Perch hunting is when the eagle is able to perch high up on a tree and spot potential prey. Elsewhere around Burrard Inlet these old trees have been removed so that the eagles find it difficult to nest in close proximity to their feeding areas, an essential requirement when both protecting and feeding voracious and demanding young. This has necessitated the construction by David Hancock and me of four artificial nests in the City and District of North Vancouver. Hopefully this will never be required in West Vancouver.
Living tree roots are a major stabilizer of slopes, but dead tree roots in a logged coniferous forest lose 75 per cent of that soil stabilizing effect within eight years as the roots decay. It is the network of smaller nutrient-seeking roots that stabilize the soil, not the larger roots whose job is to anchor the trees.
Residents should not be fearful of these old trees falling if they are healthy as their root systems have developed to withstand many powerful storms that have occurred during their lifetimes. The trees are very resistant to wind-throw because of their wind-firm root system except when the tree is diseased, in which case it can be removed after assessment as a hazard tree by an arborist.
Carbon sequestration by trees relates to overall leaf area which increases as the tree grows. This means bigger, older trees absorb more carbon from the atmosphere.
The big trees of West Vancouver are a major part of what makes the district an attractive and healthy area to live and should be carefully managed while understanding their role and biology.
David Cook
Biologist
North Vancouver
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