How to Thin Your Woods

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Go through the appropriate steps before thinning your woods.

Credit: Helen H. Richardson, The Denver Post

Thinning shapes your forest and guides its growth for years to come. If it’s not done the right way and at the right time, it can do more harm than good.

But it doesn’t have to be intimidating or difficult. With the right information and support, any woodland owner can plan a safe, successful thinning. This step-by-step guide can help.

Before you thin:

• Talk to your forester. A trusted forestry professional can guide you through every step of the thinning process. He or she will be familiar with soil and climate conditions where you live, the needs of the specific trees on your land, and the ins and outs of your local timber market—all of which will factor into your thinning.
• Take stock of your trees. Walk through your stands, and use aerial photographs and your management plan if you have them. Map out how many trees are on each acre of your woods, the species, diameter, height and age of each tree and what condition it’s in. Note signs of stress or disease (such as cankers or dying leaves), insect problems, and whether the tree is crooked, twisted or otherwise deformed.
• Take stock of your land. Note whether there are areas with fragile, sensitive soils, or slopes that will make it more difficult to access your trees. Coastal areas or high, windy ridges will also require special attention.
• Define your goals. Do you want to create healthy wildlife habitat? Will you be grazing livestock in your woods? Are there specific tree species you want to encourage or protect? Are you interested in growing trees for commercial timber? Your goals—and they may include none or all of these possibilities—will determine how you thin your woods. Figure out your objectives before you plan your thinning.
• Choose your keepers. Once you’ve decided on your goals, select the trees that will help you meet those goals. In general, you’ll want to keep larger, higher-diameter, straight and healthy trees, and remove smaller, invasive, crooked, damaged or sick trees. If your goal is timber production, focus on keeping desirable, marketable tree species. If creating wildlife habitat is a priority, make sure to leave some of the hollow, dead trees (called “snags”) where animals like to nest and live.
• Space accordingly. Your goals will also determine how you space your “keeper” trees. You’ll want to keep about 10-30 feet of space between trees, depending on the species and your local conditions. If you’re interested in grazing livestock, hunting big game or growing very large-diameter trees for commercial timber, more space is desirable. Your consulting forester can advise you on the specifics of your site.
• Decide who does it, and how. Will your forester conduct the thinning, or will you do it yourself? Are your trees valuable enough for a commercial thinning? You’ll need to decide this before you begin. If you plan to hire a contractor, you will need to find one with the appropriate experience, insurance and price for your needs. If you plan to thin your woods yourself, you will need to get the right equipment, training and permits to proceed.

You can remove unwanted trees with chemical tree killers or by mechanical means. Axes, machetes or shears may be adequate for mechanically removing trees with diameters less than an inch or so. You will most likely need a chainsaw for thinning larger trees, and very large trees will require specialized equipment. You will also need a hard hat, gloves, leg protection, steel-toed boots and eye and hearing protection for your safety. Your forester or local extension service will know about chainsaw safety courses and local requirements for permits.

When it’s time to thin:

• Size matters. It’s best to thin a stand of trees when they average 2-10 inches in diameter at breast height (that’s 4.5 feet above the ground) and 10 to 20 feet in height. At that stage of growth, the trees that are left behind will respond most rapidly to the increase in their space and resources. If you’re thinning the stand yourself, you may want to stay in the 2- to 4-inch diameter range, where removing trees is still fairly easy and inexpensive.

It is possible and sometimes desirable to thin when trees are larger and older, but it depends on the species. Ponderosa pines and Douglas firs do well even with later thinning; lodgepole pines don’t.

• Timing matters too. Don’t thin in spring and early summer, when tree bark is most susceptible to damage. A “keeper” tree with scraped or damaged bark will be vulnerable to rot and insect infestation in the hot months to follow.
• Caution is key. Strive to disturb your soil and your keeper trees as little as possible throughout the thinning process, and use every precaution to keep yourself safe.

After you thin:

• Deal with your stumps. If bark beetles are present in your area, you may want to remove the leftover stumps of culled trees as well, as these can attract the insects. Stumps are also a concern if you’re trying to suppress the growth of hardwoods, because hardwood trees can sprout from leftover stumps.
• Don’t forget your slash. Slash is the residue—logs, fallen branches, leaves, etc.—left behind after your thinning. You can choose to burn the slash, lop and scatter it or simply leave it where it is. Leaving the slash as-is is good for the soil, as the residue will decompose and slowly return nutrients to the earth. But large piles of slash can fuel wildfires and restrict access for you, your livestock and your wildlife.

Lopping and scattering involves cutting up and distributing the slash so it’s more evenly spaced as it decomposes. This technique restores soil nutrients too, but it takes additional time and labor and nevertheless raises your wildfire risk.

Burning your slash is also good for the soil—ash can encourage growth—but you must have the skills and permits to conduct the burn safely and legally, and you must avoid burning during wildfire season.

• Keep an eye on things. Once your thinning is complete and in the months and years to follow, you’ll want to track how your trees respond to the thinning. Did you achieve the goals and objectives you had when you began the process?

If your woods have larger trees (in the 5- to 10-inch diameter range or higher) and desirable tree species, there may be a market for your unwanted trees. A commercial thinning is much like a regular (pre-commercial) thinning, but with a few special considerations.