Wood Business

A treemarker’s tales: Silviculture by spray paint

March 23, 2023  By Elliott Groen

Tree marking is silviculture by spray paint: a science and an art where the canvas is only touched in increments that span decades. Photos courtesy of Elliott Groen.

My eyes are constantly moving as I walk with a slow and steady shuffle across the glacier carved hills and valleys of the Great Lakes-St Lawrence forest region. The weight in my vest gradually dwindles throughout the day as I empty spray cans, water bottles and lunch supplies. I paint rings around trees, guiding harvest operations to emulate natural disturbances such as fire, wind, insects, and disease. There are clues that this has not been the first time someone has moved through this area; old, faded paint on trees on steep slopes out of reach of previous harvesting, the occasional stump, and signs of old landings and skid trails. The decisions made then have shaped the current forest condition. The decisions I am making now will impact the years to come. The weight of this does not escape me.

Tree marking has been practiced in Ontario since the late 1970s. Treemarkers implement sustainable forest management in partial harvesting systems. Single tree selection is commonly used in uneven-aged stands dominated by shade tolerant hardwoods, whereas shelterwood systems are applied to even-aged stands usually characterized by mid-tolerant species such as Eastern White Pine. Trees are marked for removal or retention under these silvicultural systems to support and enhance the health, diversity, productivity, and ecological integrity of forested stands. This is informed by a long list of scientific reasoning that is a part of forest management, including natural range variation modelling, stand and site guides, silvicultural ground rules and conditions on operations.

While decision making is grounded in science, there is also an art to tree marking. Certified treemarkers are bound by a code of ethics which includes only conducting work for which they have the experience, training, and certification. Scientific guidelines need to be interpreted on a tree-by-tree and site-by-site basis. For this reason, new treemarkers work under experienced professionals to learn how to make these nuanced decisions.

There are many stands that are typed as uneven aged sugar maple dominated with close to full stocking, but they may need to be treated differently. Tree marking in these stands is not only based on the trees that show up in the data, but also what herbaceous indicator species tell us about the site and how suitable it is for the different regeneration present. The live crown ratio, height and vigour of regeneration also needs to be considered to make the right cut or leave decision. Interpreting how tree marking can promote sound future forest conditions can be an additional challenge to interpret when invasive species complexes, such as beech bark disease, are present.


All tree marking on sustainable forest licenses (SFL) is audited by treemarkers who have at least five years of experience and have passed level two certification. A tree marking quality rating of at least 93 per cent needs to be achieved, with some SFLs having higher standards for their audits. Certified treemarkers also need to take a refresher course every five years.

I first tree marked while working for a subcontractor in between college semesters. After graduating with a forest technician diploma, I worked with a tree marking crew for a stakeholder mill on one of the SFLs of Central Ontario.

White pine marked for retention to maintain stand structure and provide enough shade to protect white pine regeneration from white pine weevil.

Since then, I have started my own contracting business. In many cases, I still cruise an area before marking it with the operational forester to develop a prescription and discuss how the variations in the forest condition should be treated. This is incredibly valuable for learning about previous treatments that have been tried in the local context. For example, in most cases, trees with infectious fungal diseases are classified as unacceptable growing stock (UGS) and are marked for removal.

However, when there is a cluster of pole wood that has regenerated in a canopy gap, experience has shown that UGS trees should be retained if the overall density of pole wood is low. Removing too many UGS trees exposes the other pole wood to sunscald and windthrow in this specific situation, which does not help achieve the overall objective of improving the health of the forest.

Another important component of tree marking is identifying values and applying the appropriate reserves around them. There are a minimum number of mast, cavity and supercanopy trees that need to be retained. Another common value encountered is raptor nests. Guidelines exist on how big of a reserve respective species need around their nests. This also depends on whether the nest is active.

The first raptor nest that I identified was an active broad wing hawk nest. I recognized the call, and the hawk led me right to its nest. In some cases, such as goshawk nests, there will be multiple levels of reserve, with modified operations allowed in the outer rings. Reserves are also commonly placed around streams, lakes, cultural heritage sites, canoe routes and where species at risk are encountered. While some of these are already mapped in many cases, it is the responsibility of the treemarker to identify these.

Tree marking is silviculture by spray paint: a science and an art where the canvas is only touched in increments that span decades. It guides harvesting operations to achieve the environmental, social, and economic objectives of sustainable forest management. It is a trade that requires constant learning and a need to hold oneself to a high standard. It is also a great way to make a living, walking through the forest and looking at trees.

Elliott Groen, R.P.F. in training owns and operates a forestry contracting business in Ontario. He was born in Canada, but grew up in the Netherlands and found his way into forestry after working as a chef, farmer and carpenter in Sweden and the interior of B.C.

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