Trees and Construction Damage

(Something I had put together when I saw our next door neighbour's house construction put a huge Norway Maple under a lot of stress)

Trees (especially in the urban environment) are a huge asset. Large trees are typically valued at $10K-$20K or more, but does that really reflect the enjoyment of the tree? Plus its air-conditioning effect on the street and houses? To say nothing of its climbability :-) Construction can obviously damage these trees and most municipalities have regulations as to the minimum allowed distance from the tree before allowing any construction, excavating, trenching, scraping, dumping or disturbance of any kind. One example of regulations are those for Toronto (see http://www.toronto.ca/trees/pdfs/TreeProtSpecs.pdf) which specify the 'tree protection zone' which is the zone within which there must be:

• no construction;
• no altering of grade by adding fill, excavating, trenching, scraping, dumping or disturbance of any kind.
• no storage of construction materials, equipment, soil, construction waste or debris.
• no disposal of any liquids e.g. concrete sleuth, gas, oil, paint.
• no movement of vehicles, equipment or pedestrians.
• no parking of vehicles or machinery.
• directional micro-tunnelling and boring may be permitted within the limits of a TPZ subject to approval by Urban Forestry.
• open face cuts outside a TPZ that are consistent with an approved plan and that require root pruning, require the services of a qualified arborist or approved tree professional. An exploratory dig, either by hand or using a low water pressure hydro vac method, must be completed prior to commencing with open face cuts outside the TPZ.

Certain types of trees are also more or less sensitive to root damage (see this link for info on tolerance of tree roots to damage) and may require additional distance and care. A tree's essential root system will be out to roughly the ‘dripline’ (the radius of the canopy of the tree) and ideally there is some protection out to this distance. Hope this helps those who have been wondering just how to quantify what protection needs to be given to our trees!