Old-Growth Features in your Woodlot
By Linda Touzin, Ontario Ministry of Natural Resources

“...Old-growth ecosystems are important because they are the ultimate expression of the natural processes which define and create our forest environment and the particular ecological characteristics of those species and associated flora and fauna. They are the ultimate expression of the ‘natural forest.’” Environmental Assessment Board, 1994, p. 385

Old-growth forests have been expressed in many terms such as old, ancient, virgin, late-seral, over-mature and pristine. You may have heard these terms before and have an image in your mind of what old growth looks like.  The image that each of us has may differ.

Many people have never had the opportunity to visit an old-growth forest but have seen images in the media. There is no denying that old-growth forests are unique and rare ecosystems.  They have an abundance of diverse species. 

It is widely agreed that age is only one, albeit important, of many factors needed to define the term “old growth.” Old growth also refers to natural ecosystems that are the result of a lack of large-scale disturbance over a long time.

Age is a relative term.  Old growth for one tree species may not be old growth in another.  For example, in central Ontario, balsam fir may be “old” at 70 years of age and only live for another 40 to 80 years. However, hemlock begins its old-growth phase at approximately 180 years of age and can live for another 500 years or more. White pine may enter its old-growth phase earlier in Northern Ontario than in southern Ontario.

The age at which different tree species exhibit old growth characteristics is called the “old-growth age-of-onset.”  This stage of growth is determined by the minimum age at which the tree is close to attaining its maximum diameter.  The duration or persistence of old-growth conditions is the length of time after the age-of-onset that the species is expected to live on a given site.

If a species is considered short-lived, its age-of-onset is at a relatively young age. If a species is long-lived, its age-of-onset is at a much older age. A few examples of tree species in Ontario that are short-lived are poplar, white birch, balsam fir and tamarack. Long-lived species include white pine, white cedar, hemlock, sugar maple, yellow birch and American beech.  Data has been compiled from many sites across the province to determine age-of-onset and old-growth criteria for major tree species in Ontario. 

Although an old stand of a short-lived species such as poplar may have old-growth characteristics (such as old trees, declining trees and snags), these stands are generally not regarded as old-growth forests. They are seen as being in a transitional stage of succession.

On Crown lands in Ontario, forest managers must follow the direction provided in the Old Growth Policy for Ontario’s Crown Forests and identify old-growth forest stands using the guidance in the Old Growth Forest Definitions for Ontario.  They must specify objectives and targets for old-growth forest stands, based on the historic and current forest conditions of the particular forest they are managing, and in consideration of the landscape pattern these old-growth forest stands present.  A few specific examples of old-growth conditions that must addressed in the objectives and targets are:
  • biological diversity;
  • forest-age class structure (now and into the future); and
  • old-growth structural diversity within stands.

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The long-term assessment of the sustainability of critical wildlife habitats provided by old-growth forest ecosystems is also undertaken. 

Old-growth forests were initially thought to be important because of the critical wildlife habitat they provided.  Scientists studying old-growth forests now see the potential role these forests have to play as reservoirs of genetic diversity.  These forests may act as important gene pools for the dispersal and maintenance of tree species.  As more studies are undertaken in these “natural laboratories,” these forests are found to be more complex than initially understood.  Great consideration needs to be given to the maintenance of these older forests, and the provision of forests to become old growth, so that more can be understood.


Other factors that characterize old-growth forests are:
  • the presence of large, old trees (particularly of long-lived species);
  • mixed ages;
  • multiple canopy layers;
  • canopy openings;
  • pit and mound topography;
  • standing dead trees and declining trees;
  • wood on the forest floor in various stages of decay; and
  • minimal disturbance (no signs of human disturbance).

These characteristics provide a variety of habitats that in turn sustain a wide array of organisms. 

Although specific direction doesn’t exist for the identification, enhancement or restoration of old growth, and old-growth conditions on private lands, much can be done in your woodlot to maintain, enhance or restore old-growth characteristics and to help your woodlot reach an old-growth state. 

Old Trees and Large Trees

a) These are trees that have been in the forest since the stand reached the climax stage of succession. Usually, older trees are the larger trees, but not always. You might recognize these as veterans by their size--survivors of past logging operations or natural disturbances such as fire.  Some may be supercanopy trees, which means that they tower over the main tree canopy.  Many times, it is by these large, old trees that an old-growth site is first recognized

A white pine supercanopy tree.

b) Old trees and groups of old trees, particularly in large contiguous areas, provide very specific habitats for wildlife.  Supercanopy trees provide perching and nesting sites for bald eagles and ospreys.  Black bears may also use them for bedding or refuge.

c) Leave a section of your woodlot untouched. If you are harvesting this area, try to leave a good number of larger trees.  Retain a higher residual basal area.  Wait longer between return harvests and keep the residual basal area higher than in regular harvests.  Do not harvest stands until they are at least 28m2/ha and retain at least 20m2/ha on site after harvest.  Leave at least one supercanopy tree, which is at least 60 cm diameter at breast height, for every two hectares.

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Multiple Layers and Mixed Ages in the Forest Stand

a) Old-growth forests have many different layers of trees and shrubs.  Old growth is often comprised of supercanopy trees, veterans, dominant and co-dominant trees, intermediate and suppressed trees, and advanced tree regeneration.  The understory is smaller trees, shrubs and herbs.  These layers can also represent mixed ages, the results of natural disturbances, individual tree mortality and natural succession.

b) This multitude of layers results in a stable ecosystem and the stand-structural diversity that is important to wildlife.

c) During harvest operations, retain trees from all size classes and, if possible, keep larger size trees that will become old growth.

Canopy Openings

These are gaps or holes in the upper canopy that allow light to reach the ground.

a) Gaps in the tree canopy of a forest are created when individual trees (or small groups of trees) fall over or are removed by natural processes such as disease, fire, ice and wind. You will recognize a gap by the light reaching the forest floor.  Gaps can be in a variety of sizes depending on the number of trees removed from the canopy and the size of their crowns.

Gaps in the forest canopy.

b) Even old-growth forests have gaps in them where younger trees can grow.  The additional light allowed in by a gap will aid forest regeneration.  Regeneration in small gaps in the forest provides valuable habitat for species such as the black warbler, white warbler and red-eyed vireo.

c)  During harvest operations, create variable-size gaps that range from 0.02 to 0.20 hectares.  An Ontario-certified tree marker would recognize the appropriate site conditions where this can be done.

Pit and Mound Topography

a) Pits and mounds are created when a tree is uprooted, falls to the ground and is left to decay.  The pit is formed where the roots and attached soil have been pulled from the ground.  The roots decay to form the mound.  Pits and mounds can be of various sizes, depending on the size of the tree and its root system. 

b) When the roots are pulled from the ground, fresh mineral soil is exposed.  In the depression, moisture and fallen leaves often collect, creating a special habitat for certain organisms to breed and live.  Pits can hold water in spring (called vernal pools), which are valuable breeding grounds for amphibians such as salamanders.  These pits also create diverse soil profiles across the forest.  Over time, the decay of trees and the depressions caused by uprooting will form the pit and mound topography that is characteristic of old-growth sites.

c) The trees themselves create the pit and mound topography. The landowner may be mindful of this microtopography and limit the coverage of heavy machinery and trails in the woodlot.  Harvesting could be undertaken when the ground is frozen and covered in snow.  Livestock should not be allowed to graze or shelter in the woodlot.

Standing Dead and Declining Trees

a) Standing dead trees or declining trees in various stages of decline provide critical habitat for many birds and animals.  Standing dead trees are called snags. 

b) Dead trees, dying trees and snags are important for wildlife because these trees provide perches, roosting sites and nesting sites for many species.  If standing dead trees are located near water, great blue herons and ospreys may use them for nesting sites.  Dead and declining trees may also contain cavities that provide habitat for animals and birds to rest, nest and store food.  Squirrels, ducks, mice, owls, falcons and American marten all use tree cavities as habitat.  Brown creepers and bats may even use the bark peeling from a dead tree as habitat.

c) Standing dead trees should not constitute a safety hazard as defined by the Occupational Health and Safety Act.  During harvest operations, retain at least 12 cavity trees per hectare, with at least half of these with a diameter at breast height of more than 40 centimetres.  Also, you could girdle unmerchantable trees that were to be felled, so that these will die and become snags. Girdling involves cutting a ring around and into the tree to stop the flow of nutrients.

Landowners have been successful in attracting owls by erecting nesting boxes in areas that did not have large trees with potential for cavities.  Nest boxes can also be of value to several cavity-nesting species such as chickadees and flickers.

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Downed Woody Debris

This is sometimes called coarse woody debris, downed wood, dead wood on the ground, etc. 

a)   Downed woody debris is a term used to describe wood that is on the ground (from a fallen tree, broken limbs or tops, or parts of a tree left on the ground after logging operations). This wood is usually in various stages of decay.  It is easily recognized if freshly fallen, but over time, this woody debris will decay, lose its shape and be covered with vegetation such as mosses and other plants. 

Downed woody debris on the forest floor. 1

b) Each stage of decomposition plays an important role.  Downed woody debris provides shelter and habitat for many animals.  Hollow logs provide shelter and escape routes for racoons, hares and other small animals.  In spring, ruffed grouse often use fallen trees as their drumming log to mark their territory.  As the wood decays, it is able to absorb moisture and provide ideal conditions for the seeds of yellow birch and hemlock to germinate and grow.  As the decay progresses, nutrients from the wood replenish the soil.  This organic matter provides habitat for fungi, reptiles, amphibians and bacteria.

c) Standing dead trees and dying trees will eventually fall to the ground, producing downed woody debris.  Even though you may be tempted to clean up your woodlot, leave some debris to decay on site.  Ask your harvest operator to leave large cull logs or large cull butts of logs in the bush. And if possible, also ask your harvest operator to leave unmerchantable material at the stump.  Logs of at least 40 cm in diameter and two metres in length are ideal.

A snag left in the woodlot for wildlife habitat.

Many of the suggestions listed above are of low cost to the landowner and yet provide a multitude of benefits for the ecosystem as a whole for years to come.

Plantation owners take note. Your plantation may also have old-growth features.  Just keep in mind the special old-growth characteristics listed above.  When the opportunity presents itself, do what you can to encourage these.  Admittedly, it will take longer to reach an old-growth state!

All of these suggestions can be incorporated into your woodlot management plan as objectives of your plan. There are many qualified forest consultants available to help you.

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Looking for More Information?

To find out more about old-growth forests or to find a forest consultant, you may want to visit one of the following websites:

Ministry of Natural Resources’ website http://www.mnr.gov.on.ca/en/Publication/index.html?CSB_ic-name=topMenu&CSB_ic-info=publications_Eng and search for the following publications:
  • Old Growth Forest Definitions for Ontario, OMNR 2003
  • Old Growth Policy for Ontario’s Crown Forests, OMNR 2003
  • Landowner Extension Notes Series “Restoring Old-Growth Features to Managed Forest in Southern Ontario”

"The Old Growth Forest Ecosystem and Old Growth Forests in Eastern Ontario" is part of Caring for Your Land Series of Workshops.  It consists of a binder with a Powerpoint presentation on CD, speaker notes, presentation handouts, and additional resource information on old growth forests can be found on the Eastern Ontario Model Forest website http://www.eomf.on.ca/en/caring-for-your-land-workshops/publications/caring-for-your-land-workshop-series.

Ontario Nature’s website www.ontarionature.org and search for the Introducing Old Growth, the Ultimate Forest.

The Ontario Woodlot Association’s Landowners Forest Service’s Directory website www.ontariowoodlot.com for a listing of forest consultants working in your area.

Photo Credit

1 Paul Bolstad, University of Minnesota, United States

This article was featured in a past edition of the S&W Report, the newsletter of the Ontario Woodlot Association. 

© Ontario Woodlot Association, 2011

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