Hazard Trees: Assessing Nuisance Risk

Issue: 
May-June 2007

PAST ONTARIO ARBORIST ARTICLES by Shayne Plowman and Edward Kennedy regarding the health or quality of a tree and the worthiness of letting it stand have been quite entertaining (see the May 2006 and July 2006 issues). The point of their articles was in regard to municipal bylaw mandates and ‘tree hugger’ attitudes that encourage preservation despite genuine issues with the specimen in question. Both Shayne’s suggestion that “some trees deserve to have a house fall on them” and Edward’s comment that “some people deserve to have a tree fall on them” were humourous, yet insightful taken in context. Both gentlemen focused on the removal of a failing tree or one that lacks contribution of any reasonable value or merit via its existence.

In addition to the removal considerations suggested by Shayne and Edward, we should also consider nuisance. It is typical in hazard assessment to focus on fall risk by structural failure. However, what is being said about potential hazards while the tree is still very healthy?

A great difficulty in assessing ‘hazard trees’ is to recognize that there may be many inherent aspects in a healthy tree which present risk, especially those giving rise to matters of nuisance with a potential to indirectly cause injury, damage or other harm. An example that comes to my mind is a large willow (presumably healthy – I’m no arborist) along the shores of the Scugog River just north of the town of Lindsay Ontario. This tree is located a few minutes from a residential area and it is ‘blessed’ with a rope swing, providing a source of exhilarating entertainment for many children on a hot day who enjoy a plunge into the refreshing water.

So far, this sounds to be reasonably safe, common and quite pleasant. However, the concern is that this tree happens to be just around the bend at a sharp corner in the river where the approaching view is blocked by an old train bridge. Boaters from the north approach usually at high speed (the slow zone only begins at this point) make the corner and then they are suddenly confronted with the challenge of avoiding swimmers (of course, boats don’t have brakes). Additionally problematic is that the tree is located on the far side of the river from the residential areas. The kids must swim across the river, right through the boating path, to get to the swing. This particular situation is one of ‘attractive’ nuisance, whereby the tree itself poses threat by nothing more than its inviting appeal. Admittedly, I haven’t been boating in that area for a few years now and I wonder if the town or the Trent-Severn Waterway has removed this tree. Of course, I can also see argument from conservationists on the need to keep this particular tree as it may be providing erosion protection and shoreline naturalization benefits.

The tree mentioned above likely poses little risk as a direct cause of harm but instead a major risk as an indirect contributor. Children only play in that part of the river because that is where the tree is. However, in many cases of nuisance, a tree will pose a more connected risk such as the potential ‘damage’ that can occur from its shedding of debris, growth of root systems or even moisture absorption. Does its fruit attract dangerous insects or wildlife that could harm a family pet or child? May autumn leaves threaten to block eaves or storm drains that could ‘give rise’ to water damage? Is ‘trip & fall’ a concern due to roots that might cause upheaval damage to nearby walkways? Will a tree’s growth and natural thirst reduce groundwater penetration, possibly resulting in dehydration of clay below and consequential settling damage to nearby structures (crack a pool or basement)?

It can clearly be recognized from the concerns above that there are many examples of a ‘hazard’ tree, many of which have nothing to do with the health or quality of the tree itself. As self-promoted ‘experts’ specializing in hazard tree assessments, the consulting arborist should consider nuisance risks. Also, as it is difficult to foresee all potential concerns, errors and omissions insurance protection should be very carefully considered!

— Scott McEachern, Program Executive, TREESURE provided by: Hugh Wood Canada Ltd., smceachern@hwcanada.com

Our mission is to enhance and promote the care and benefit of trees for present and future generations in Ontario through education, research and awareness.