Forest Health

Forest health encompasses many factors and a number of components. For example, a healthy forest includes healthy soils, water, plants and a functioning ecosystem.  A dying or dead tree or a rotting log on the forest floor are parts of a healthy forest. Tree health focusses on what is traditionally referred to as forest health.  Tree health can be affected by many abiotic factors – mechanical wounds, soil compaction, impacts of acid rain, the effects of heavy wind or ice damage, sunscald, drought, late or early frosts and forest fire and, by extension, climate change.

Most discussions about tree health deal with insects and disease are a known together as forest pests.  Some forest pests can affect a wide variety of species – e.g. forest tent caterpillar will defoliate aspen, maple and other tree species – while other pests are very host specific – i.e. Beech Bark Disease only affects beech. Some pests may attack a variety of conifer species, while others a variety of hardwood species and a few may attack conifer or hardwood trees.

Some pests:

This website can only highlight a few forest pests. It should be noted, however, that some forest pests may only weaken a tree allowing other forest pests to successfully kill a tree.  Quite often, especially with defoliators such as fall webworm and forest tent caterpillar, trees survive with little lasting ill effects.

Beech Bark Disease consists of a combination of an insect and a fungus. Beech scale insects infest beech trees and make them more vulnerable to the Neonectria faginata fungus. The disease leads to high levels of beech tree mortality and a declining beech population. This disease is currently found in the southern portion of the French-Severn forest.

Westwind partnered with the MECP and Muskoka Watershed Advisory Group on a forest restoration project on private land tolerant hardwood forests impacted by beech bark disease. Click here to see the educational brochure for landowners and managers was produced.

White Pine Blister Rust is a fungus which affects white pine trees. Seedlings are most vulnerable to the disease and more likely to be killed. White pine blister rust can also kill branches or tops of larger trees or kill the entire tree if the infection girdles the trunk. White pine blister rust is currently found in many parts of French-Severn forest.

Sawfly larvae are defoliators that feed on the needles and foliage of trees. There are many species of sawflies which feed on diverse species of trees. Some species of sawflies are found in the French-Severn forest.

Forest Tent Caterpillar is a native insect with defoliates a variety of broadleafed trees with outbreaks occurring in 10-12 year intervals. Forest tent caterpillars are found in the French-Severn forest.

Hemlock Looper is a native insect which defoliates many species of trees including balsam fir and eastern hemlock.

Emerald Ash Borer is an insect which feeds on ash tree species. It was first found in Ontario in 2002 in Windsor and has since spread to areas as far north as Sault Ste. Marie and as far east as Ottawa in Ontario. Usually within six years of woodlot infestation, almost all ash trees have been killed. Emerald Ash Borer has not yet been found in the French-Severn forest.

Hemlock Wooly Adelgid is an invasive insect which feeds on hemlock species. It was found in Ontario between 2012-2015 in isolated locations; however, infested trees were removed. The aldegid is not known to be in Eastern Canada and therefore is not known to be in the French-Severn forest.

Asian Longhorn Beetle is an invasive insect which bores into the wood of many species of hardwoods. Two infestations have been found in southern Ontario: one which was declared eradicated in 2013 and one which is under active eradication. The beetle is not currently found in the French-Severn forest.

Mountain Pine Beetle is an insect which is native to western North America which excavate galleries in predominantly pine species. Despite being found in northern Alberta and an isolated population of pines in southwestern Saskatchewan, the beetle is not found in Ontario.

To learn more about forest pests and diseases in Ontario, please visit the following links.

Trees, insects and diseases of Canada’s forests

Top forest insects and diseases in Canada

Forest Health Conditions in Ontario 2012. Please note that insect and disease distributions may have changed somewhat since 2012; however, this report provides useful information in understanding forest pests and diseases in Ontario.