Finding and Reporting Old Growth Forests
Look for the following signs to identify old-growth forests in Ontario (this is a shortened version of our guide to identifying and reporting old-growth forests from the upcoming book). Details on how to report your findings are at the bottom of the page.
Pit and mound topography: Even forests that were heavily logged but never went under the plow may carry an inheritance from the forest that came before, which can most easily be seen in the soil. Is the forest floor irregular, with the large pits and mounds created by windthrown trees? Then it may be an old-growth forest. Pits and mounds last for many centuries, and often have survived some historical logging. Fields that have been plowed, however, remain flat until large mature trees can grow and be windthrown. Pit and mound topography tends to be less pronounced in sandy soils, or where trees are very shallow-rooted.
Stumps: Stumps left over from logging can still be seen anywhere from a few decades, to a century or more after they were cut, depending on the species, diameter, and location of the stump. Large conifer stumps can usually still be seen a century later, especially if they are found on a dry site.
Logs and snags: there are few surer signs of old-growth forest than an abundance of large diameter logs in all stages of decay, as well as dead standing trees (snags). This shows a long history of being left alone.
Tree branching patterns: Trees with the first branches very high up on the trunk have grown up in a dense forest of tall trees, indicating a stable old-growth forest that has been relatively disturbance-free for a long period of time. Trees that grow in the open branch out low and wide, and these branches, or some signs of them, remain long after the forest has grown up around them. This branching pattern is especially obvious when trees have grown in a permanent clearing caused by agriculture, city greenspaces, or natural oak savannah.
Tree-ring counts: Many tips for recognizing older trees are scattered through this book, but the only certain way to age a tree is by counting the annual growth rings in the wood. If you don’t have a tree-corer to extract a small segment of wood from the tree, it’s impossible to accurately age a living tree. You can make a guess based on bark, branching, etc., but you can never be certain of it. For amateur forest sleuths, who don’t usually carry a tree-corer, opportunities to age trees are usually found in any forest that has a maintained trail system. When trees fall across a trail, the resulting cut log offers the perfect opportunity to age the tree by counting tree rings. Only conifers can be accurately counted in the field, for older trees a 10x hand lens will likely be needed.
Tree size: Tree size often doesn’t tell us much, but it does tell us something. Trees take time to grow, so trees that are especially tall and wide may be relatively old, or they may be growing on a rich site, or both. In any case, finding big trees is a thrill, and it can be worth taking the time and effort to accurately measure them. Diameter is easy to measure, generally it is taken at 1.4 metres above the ground (on the high side of the tree) and can be calculated by measuring circumference at this height with a flexible tape wrapped around the tree, and dividing by 3.14. Also, hold the tape up in front of the tree and estimate diameter directly to make sure your number makes sense. Diameter doesn’t tell you much without also considering height, and height is hard to measure accurately. Ideally you will need a clinometer to measure angle, and either a long tape measure, or preferably a laser rangefinder, to measure distance. Methods for measuring height are summed up in the Tree Measuring Guidelines of the Eastern Native Tree Society, by Will Blozan (2004): http://www.nativetreesociety.org/measure/tree_measuring_guidelines.htm.
Reporting your findings: Old trees or suspected patches of old-growth forest can be reported by emailing mhenry -at- ancientforest.org. Big trees can be reported to the Honour Roll of Ontario Trees (http://www.oforest.on.ca/hroot/).