Tree inspection protocols for trails

photo: giscloud.com

At a trail based risk management course I was leading in Toronto this summer, we surveyed the land managers present on their trail tree inspection procedures, specific to high risk trees. A high risk tree is one with signs of imminent failure, which will potentially intersect with an existing trail corridor. Jurisdictions are mostly aligned with similar protocols, which are in addition to regular trail inspections:

Given urban, high use Type 1 or 2 trails (according to Parks Canada scale):

In most cases, tree inspections are performed by foresters or arbourists, separate from trail inspections.

2 tree specific inspections per year - one 'leaf on' and one 'leaf off' season
Some areas mandate special inspections after severe weather events (which are becoming more common).

Trail corridor is inspected back the height of the typical tree bordering the corridor. i.e. if 20m trees surround the trail, then trees are inspected 20m back on each side of the trail.

Particular attention is paid to congregation or collection areas on trails (where people spend more time, such as picnic areas, overlooks, trail intersections and trail heads) as more time is spent at these locations, therefore presenting higher exposure to potential high risk trees. Tolerance for high risk trees is lower in these areas.

Transit areas are considered lower risk, as user pass by these areas/high risk trees very quickly, creating exposure that is only a couple of seconds long for the individual.

Type 3 trails (natural surface singletrack) are typically visually inspected once per year.
Type 4 wilderness trails are typically not inspected for tree risk.

Ratings consider: tree species (some species fail more often than others, specific to your forest and biome); visible tree health (leaf, crown, bark); structural integrity of the single tree (size, branch unions, root area integrity).

It was also pointed out by land managers that because a tree has signs of stress it does not automatically get removed. Standing dead trees provide valuable habitat for certain species, so the tree's risk to trail users is assessed in its entirety. Potentially, a dead tree can stand for several seasons before it shows imminent signs of falling.

Likewise, it was also discussed that given severe weather, perfectly healthy trees can be uprooted or broken up the trunk.

As per trail inspection, all work is documented with an associated chain of responsibility to authorize action on the inspection's findings.

Check out the Toronto Region Conservation Authority's tree protocols. It does a good job of outlining the risk variables in assessing a tree. Link here.