I’ve been helping a friend thin his half-acre woodlot. The thinning process presents a handful of challenges.

First, and most important, the process must begin with answering the question: What is the objective?

A landowner may choose to thin a woodlot for any of these reasons:

• Produce firewood and/or lumber as a crop.
• Thin out weak or diseased trees.
• Remove excess trees and undesirable trees so remaining desirable trees have greater access to moisture, sunlight and soil nutrients.
• Encourage wildlife by nurturing trees that attract squirrels, songbirds or other animal or bird species.
• Select trees for aesthetic purposes such as colorful foliage, attractive flowers or unique bark.

My friend’s woodlot had grown up naturally with a half dozen species of trees, many of which were growing too close together.

The woodlot contained red and bur oak, hackberry, green ash, basswood, red cedar, elm, buckthorn, prickly ash and gray dogwood, along with woodbine, poison ivy and wild raspberry growing at ground level.

My friend’s objective was to reduce the density of the tree stand and remove all but the healthiest and most-desirable tree species.

In this situation, we selected the healthiest and best-structured bur oaks, red oaks and ash, and began removing everything else. Most of the trees ranged in trunk diameter (four feet above the ground) from 12 inches down to the thickness of a finger.

One of the toughest decisions is to decide how much space to allow between trees following thinning. Before thinning, the woodlot ground is completely shaded by tall, skinny trees that are all growing vertically in their attempt to reach sunshine. When trees are thinned, sunlight begins to penetrate more deeply towards the base of trees and the “released trees” begin filling out their canopies (growing lateral branches). This will be a gradual process, requiring 3-5 years before the ground is once again shaded.

When trees that are now 10 feet apart spread their branches laterally so a dense canopy exists once again – maybe five years from now – the woodlot will have to be revisited to determine whether more thinning should occur. At that time, it is possible that half the remaining trees should be removed to make room for the remaining healthiest and most-structurally sound trees on the property. At this stage, the remaining trees may well be spaced by 20 feet rather than 10 feet. Of course, the decisions made five years from now should be based upon what the objectives are at that time.

For our current project, we chipped up all the harvested trees with the intention of spreading the wood chips on the soil surface of the woodlot. This wood mulch will help keep roots of the remaining trees moist and cool and also help to control weed growth as more sunshine reaches the ground.

We cut trees off 1 foot above the ground with the intention of returning to the woodlot in early spring, when trees break dormancy, and cutting the remaining stumps near ground level. At this time, stumps can be treated with a herbicide to prevent harvested trees from sprouting new growth from their root systems.

This process of selecting and thinning trees provides the opportunity to evaluate “keeper trees” for branching problems and enables corrective pruning so these trees will be more resistant to disease and storm damage in future years.

Thinning out a woodlot isn’t an exact science. Decisions are based on “best judgment,” along with personal preference and a little trial and error. Preference enters into the equation when a healthy 6-inch red oak is growing next to a healthy 6-inch ash. One of the two trees needs to go.

One way to make this decision is to favor diversity. A woodlot will most likely be healthier over the long haul if it contains multiple species of trees rather than just one species. Our thinning process left bur oaks, red oaks, ash and a few basswoods, even though the property could have been thinned to just include the two oak species. Diversity makes sense as a precaution against present and future disease threats that target individual tree species.

Woodlots need to be managed because competition among trees in a dense stand can result in slow growth of all trees and death of the most-desirable trees.

After thinning, the released trees become healthier and more vigorous, more insect and disease resistant, grow faster and produce the benefits matching the landowner’s objectives.

If you have questions about thinning a woodlot, I can be reached at cliff@puttingdownroots.net.