‘Tree felling’ and ‘conservation’ may seem like odd bedfellows. For many, the image that first comes to mind is the mass deforestation of tropical rainforests–and the loss of ecology associated with rainforest loss. This image that the media has rightly raised to the forefront of public awareness is, however, an extreme. Like so many extremes, we lose the subtleties and nuances of the science involved.
In the forests of southern Ontario, we should learn more about the ‘good news’ story behind the removal of trees. Felling trees is a vital part of conservation: it’s a tool that supports the trees and forests that we value for their beauty, recreation, their services of providing clean air and water, and also to protect and maintain species and ecosystems.
The story behind tree felling is more complex than you might imagine. It is in fact, a science – the science of silviculture. Silviculture is the science of producing and tending a forest. It’s the theory and practice of establishing a woodlot, controlling the composition of species, and supporting the growth and quality of a thriving forest to meet the objectives of the land manager. Silvicultural practice predominantly relies on the removal or harvesting of trees as a means of maintaining forest cover.
There are three main forms of silviculture, and each form serves a valuable role in the right forest, at the right time and for the right reasons – and yes, clear cutting is one of them!
Let’s start with the one you will see most often in the Halton watershed, and that is most frequently used by the forestry professionals at Conservation Halton: the use of selection thinning.
As the name indicates, it is indeed very selective. It is used in forests where there is a diverse mix of tree ages and that mix of ages is supported and encouraged. Trees are cut individually or on a small group basis, and it is tailored by the forest manager to encourage the growth of a specific species or forest type. It’s used to meet multiple forest objectives. This system favours the mixed hardwood deciduous forests that we have in Halton. Shade-loving species do well in this system, but in the hands of a skilled forest manager, openings are created within the continuous forest, which allows the establishment of sun-loving species like oak.
Selection thinning is the system of choice in a forest that supports important natural habitats and recreational interest – fewer trees are removed and the forest cover is maintained. The process of thinning is more challenging – the forest manager has to assess and select trees, and then remove both the felling of the tree and the removal of the log– with minimal damage to surrounding trees. By following the best practices and adhering to guidelines such as those from the Ministry of Natural Resources and Forestry, selection thinning promotes wildlife and also protects many species by limiting damage and retaining cavity trees within the forest.
The second method we will explore is the shelterwood management. The shelterwood system harvests trees over two or more cuts, each cut removing groups of trees and works in forests of an even age stand. This system mimics natural events that remove sections of a forest – wind storms, natural fires (such as those triggered by lighting), ice storms, disease and insects. The shelterwood system is suited to our mixed hardwoods and conifer woodlands. The shelterwood system has the benefit of creating openings where natural seed sources stand the best chance to support natural regrowth and regeneration after removal. It relies on a forest with healthy, robust seed producing trees.
Usually undertaken as a two cut process, it is actually a three cut process – it is not unusual for the first stage to be skipped or combined with the second. A preparatory cut is used by the forest manager to support the largest, healthiest trees to thrive – removing trees around the strongest trees to maximise their canopy growth and seed production ensures a rich seed mix to support regeneration. A second cut is known as the seed cut and sees a forest manager remove approximately 50% of the mature trees which allows light to flood to the forest floor and encourage regeneration. Once these seeds have established and reached an acceptable height, the forest manager returns to remove the remaining mature trees. This system develops a mixed forest with light and shade and encourages rapid regeneration. Typically, the whole cycle takes place over a 20-30 year span.
The final form of silviculture, and often the most misunderstood, is the clear cut. As the name suggests, this process removes a large number of trees in one section at the same time, and like the shelterwood system, clearcuts work in forests of a narrow age range (where the trees are more or less the same age, height, diameter etc). Clearcutting has a unique effect in a properly managed forest. When forest managers cut a large gap into the forest canopy, the sun shines strongly on the ground through the opening which has been created. In a carefully planned and managed forestry plan, the forest managers want the sun to shine on the ground to promote growth. Some species of trees like jack pine, black spruce, cedars, and poplars are shade intolerant: they need full sun throughout the growth cycle to flourish. Tops and seeds are left on the ground to provide the source for regeneration. Forest managers prompt rapid growth from shade intolerant species by way of clearcutting. Clearcutting mimics major natural disturbances like large wildfires, disease, and infestations. You will only rarely see clearcutting in southern Ontario, because natural disturbances on the above scale don’t usually occur in the mixed hardwood systems like we have in Halton Region. The cycle of clearcut is 30-50 years depending on species. Clearcutting is much more common as a method in the Boreal forest, which occurs in Northern Ontario.
In short, in all three types of silviculture systems, the forest manager is trying to replicate a natural process that best supports the forest type, and to maintain a productive forest. Then why do we interfere with nature instead of letting it take its course? Ideally, this would be the best case scenario – but unfortunately this relies on the removal of something else from the landscape – humans! Our pressure on forests has caused the once continuous forests that stretched over Southern Ontario to be confined to small pockets – where we must eliminate and manage the natural process such as disease and fire in order to maintain these smaller pockets of woodland. In a large continuous woodland, the loss of a few 100 hectares of forest here and there is not a big concern– but in our human driven environment, this would be devastating. So we must, on a micro-scale, mimic nature to maintain what’s left of what were once vast forests.
One tree species in a woodlot isn’t necessarily a healthy woodlot. For a resilient landscape, we need biodiversity. Monocultures, such as a forest of only ash, or only oak, or only poplars, or spruce, or pine, are susceptible to invasive species, disease, and climate change. Since different tree species grow at different speeds, and have different tolerances for sun and shade, the quick regeneration species grow more quickly and provide shade and nutrients to shade-loving species (called successional species) which eventually die out and become wildlife habitat. In the face of climate change, monocultures are not as resilient to powerful storms and weather changes as a diverse woodlot would be. To prevent monocultures, forest managers will carefully plan the seeding and planting after a cut to replenish biodiversity. Whether forest managers use clearcutting, or shelterwood, or the selection system, it is in tandem with seed cycles and/or planting to promote biodiversity and establish a healthy woodlot. Silviculture systems can help transform monocultures (like pine plantations) into a more natural, biodiverse, mixed wood stand.
Key in all this is the role of the forest manager and we are lucky at Conservation Halton to have a skilled professional team of technical staff and arborist staff who are charged with maintaining our forests. The forest manager is vital to the application of a silviculture system. Choosing an effective harvest method requires technical knowledge, expertise, and experience. The science of growing trees is complicated. For example, only certain species will respond to a particular method. If a system like clearcutting is used for shade tolerant species, like maple or hemlock, the seeds or seedlings won’t survive as well. Other factors like terrain, climate, and use of the stand (for example, recreation) are a few of the many factors a forest manager needs to take into account.
Similar to how a rosebush needs pruning to thrive, so do forests. Forest removal has been overused in certain environmentally sensitive areas in commercial settings in the past to the point that the bad press overshadowed the importance of silvicultural operations. Contrary to the public belief that has arisen from commercial overuse, cutting down trees can promote growth, regeneration, and biodiversity so long as the practice is used as a tool in a carefully managed forestry plan. Hopefully with time and information, the public will understand how a forest can thrive even more if a little pruning is used.
Last modified: September 5, 2017