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Thinning a Woodlot: How Do We Know Which Trees to Mark for Harvest?

I have been assisting landowners with the management of their woodlots for over 25 years. As foresters at Kretz Lumber Co. Inc., we spend most of our time within northern hardwood stands marking timber for harvest and setting up timber sales for the landowners we serve. We do this while producing timber products that are used in our industry as well as sawlogs for our hardwood sawmill located in Antigo, WI. We also harvest other timber types but for the context of this article, I am going to keep the focus on northern hardwood thinnings.

In my initial meeting with woodland owners I have been asked many times, “How do you know which trees to mark for harvest within a thinning of a woodlot?” I answer this by first asking them, what are your objectives and goals for your woodlot? Is it good forest management, wildlife viewing, hunting wildlife, income, recreation, or something else? By knowing the landowner’s goals, I am able to gel these goals within the setup of the timber sale and what trees to mark or not mark.

For instance, if a landowner has a goal of enhancing hunting opportunities and has only a few nut bearing trees on the property such as oaks, this information will guide me to not mark those oak trees for harvest. (An exception to this would be if the oak was showing signs of dieback.) The acorns that these trees produce can then be food for whitetail deer during the fall and early winter. Meeting landowner goals is the most important objective that we have as foresters. We want to please landowners during and after each harvest.

What you should also know is that as a general rule, we do not look to cut stems within the woodlot that have good form (tall, smooth in appearance) that may improve in grade or value over time, typically by growing to a larger diameter. I say this all the time, but think of your woodlot being similar to your home vegetable garden. What happens when you let your weeds grow too long in the garden? Answer: Your vegetables do not grow to their maximum capacity that summer.
The same holds true for a woodlot except that we are working with a longer term crop. Without timely thinning every 10-15 years, the vegetables, or as foresters call them, crop trees, will not grow to their maximum capacity. Foresters identify crop trees to not cut within a thinning and will want to grow these crop trees at the fastest rate for decades until they reach maturity.

Let’s summarize to this point: Landowner goals guide the overall setup of the timber sale. Forester’s want to grow the vegetables (or crop trees) in the garden.

I bet you are a little surprised that all I have discussed to this point are trees not being cut. It is important to know that we harvest trees with a purpose of improving the trees left behind in a hardwood thinning. But what about the weed trees we need to mark for harvest?

Forester’s identify weed trees to cut to improve the growth rates of the crop trees that are left in the forest. Here are many examples of weed trees to mark for a harvest in a hardwood thinning:

  • Poorly formed trees at risk of breakage in a windstorm
  • Defective, poor quality trees that do not have the ability to improve in quality over time
  • Unhealthy trees that have a disease
  • Trees that are at risk of insect invasion, such as Emerald Ash Borer in our Midwestern states
  • Economically mature trees that will no longer improve in graded quality by leaving them for a longer period
  • Suppressed trees that have low vigor and interfere with the crop trees growth
  • Less desirable species
  • Trees to improve spacing within the woods

There are many other principles that guide foresters scientifically within a thinning operation that are outside of the scope of this article. However, I hope this article gives you a basic understanding of what we try to accomplish when working in your woodlots and why we choose most of the trees to be harvested. As always, if you need assistance, do not hesitate to contact one of our Kretz Lumber Co. Inc foresters on staff.

Economically mature 22 inch diameter basswood tree

Unmarked tree on right is the Crop Tree. Blue marked tree to be cut is the weed tree:

Crop tree and weed tree

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