The Truth About Thinning Your Deer Woods

The goal of each individual in a species is to have its offspring survive long enough to mature and reproduce themselves; thereby perpetuating the species. Wildlife population growth generally is divided into two categories: r-strategists and K-strategists. I’ll begin by explaining the difference in how each category reproduces and cares for offspring.

The r-strategists put a lot of effort and resources into producing many offspring, that are simply “dumped” into the environment so that enough survive to the next generation. There seldom is much parental care for these species. The Atlantic Salmon is a good example; they fight their way to the breeding waters, mate, lay their eggs and die. The “r” in the title refers to an equation population ecologists use to designate reproductive rate, r.

Contrary to this, the K-strategists put a lot of effort into assuring their offspring survive into the next generation. Parental care often is intensive, so there can only be a few young produced by these species. The “K” in the name of these species comes from the designation of carrying capacity, K. The r-strategists are influenced primarily by their physical environment, while the K-strategists by the quality of their habitat.

The white-tailed deer is an excellent example of a K-strategist! In most cases, a doe produces two fawns each year, spends up to four months nursing them and another 6-8 months providing parental supervision. She seldom makes it through this time with both fawns, but her goal is to bring at least one to reproductive age. Being large herbivores, white-tailed deer are regulated by the quality of forage available throughout the year. A whitetail’s world lies from ground level to 4.5 feet above, what I refer to as the “Deer Zone.”

DIRECTING SUNLIGHT TO THE DEER ZONE

Everything a deer needs nutritionally has to lie within the deer zone or fall into it; and it is the place where the majority of deer habitat management must occur! Forage (browse, weeds, grasses and mushrooms) is the mainstay in the deer diet, and it is safe to say the three primary determiners of forage production are soil minerals, moisture and sunlight.

Scientific habitat research has clearly supported that manipulating the availability of each of these three key elements will significantly affect both deer production and antler quality on your property.

Unless you use a lot of fertilizer or irrigate, sunlight is the easiest of the three to manipulate. I often have said that deer habitat management is a “war against vegetation” in most of the whitetail’s range. The primary culprit in this war is the process of ecological succession; defined as a stepwise process in which one ecological community prepares the way for and is replaced by another.

Here is a simple explanation. A tornado devastates a stand of trees, reducing the forest to a mess of tree stumps, logs and debris. The succession process begins immediately. Seeds are transported into the area by wind or seed adaptations that get them carried by a cooperating agent, such as the feces of animals or by hitching a ride on such creatures. The seeds are also already there as a “seed bank” that may have been there for hundreds of years.

In no time at all, the devastated site is lush with weeds and grasses, along with root sprouts from some of the original trees and shrubs. Minerals are readily available, along with soil moisture, so the responding vegetation is rich in nutrition for herbivores such as deer. However, in a short time, this early “pioneer” community paves the way for another one that quickly over-tops and shades them out of existence!

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How long this takes depends on where you are climatically, but for most of the deer range, it takes from 7-12 years for this to happen. Obviously, if we are to efficiently manage whitetail habitat, we will have to regulate forests and brushlands to assure that forage remains available to our deer on a sustainable basis.

The only way to assure sustainable forage in the deer zone is to implement strategies that either maximize or optimize the amount of light reaching the deer zone. Obviously, this could be done quite simply by totally clearing the forest to the ground every 7-12 years, but that would be costly economically and ecologically! And, the result would not be complete deer habitat, which includes cover in the form of screening, winter thermal and summer thermal.

Then there is the concept of multiple-use and ecological diversity that come into play. So, the correct solution is to regulate the amount of light reaching the deer zone as the forest or brushland matures — which also benefits the many tree and shrub species occupying a specific location by reducing competition for resources.

I tell my students there are only two conditions they will encounter when developing habitat for whitetails: places with existing forests and those without forests. In the first case, you will have to manage the existing density and composition of the stand of trees; and in the second, you will have to establish a new forest, then do the same thing. Now, let me explain how.

THINNING DEER WOODS

The deer woods can be improved dramatically by regulating the density and species composition of the existing trees. That is pretty easy to say, but what exactly does that mean and how are you going to do that?

In general, trees must be removed as part of the process. Whether planted artificially by foresters or regenerated naturally after a disturbance, there always will be more trees than needed. I worked for over four decades with some of the best wildlife researchers on the planet! Our research was aimed initially at determining the optimum density of trees to provide both timber resources and deer forage.

We learned that the perfect deer woods could be described in two ways. The first was the species and density of trees, expressed as trees per acre; and the second was using a forestry term called “basal area.”

Basal area can be explained as the total cross-sectional area occupied by the tree trunks on a per acre basis. To visualize my definition, imagine a stand of trees growing up out of the ground, and topped by crowns with limbs covered by leaves. Now, cut one of these trees off at the ground and measure the diameter of the trunk at ground level.

Let’s say it is two feet, to make things simple. The area of a circle is calculated by the formula, A= πr2; where π= 3.14 and r= the radius of the stump. Then the area in square feet of that stump will be 3.14 X 12, or 3.14 ft2.

Well, that is nice, but now what do we do with the number? That’s only one tree on an acre, so we have to measure all the trees on that acre, calculate the average diameter and use the formula to calculate the area occupied by the average tree on that acre. Let’s say it turns out to 3.5 ft2; and we also counted 80 trees on the acre. An acre contains 43,560 ft2, and our 80 trees occupy a “grand total” of only 280 ft2 (0.6%) of that acre.

So, how on earth could that have any effect on how much light gets to the deer zone? When you factor in the crown diameter of each tree, the shade effect becomes significant. The combined knowledge of forestry researchers concluded that a basal area exceeding 70 ft2 for pine forests and 50 ft2 for hardwood stands is the upper limit for optimum deer forage production.

To put this into perspective, we commonly see basal areas in pine plantations of 140-plus! In such stands, a deer would have to “carry a sack lunch” to survive! Clearly, thinning of timber stands is one of the most important deer habitat management tools we have. Yet, I still haven’t told you how to thin your stands! There are two ways, as follows.

USING A 10-FACTOR PRISM

There is a small, simple device that foresters have used for many years to measure the basal area of a stand of timber — the 10-factor Prism. It is a small, wedge-shaped piece of glass that will tell you quickly the basal area of a timber stand.

You can set up a series of transect lines through the stand, stopping periodically to use your prism. Hold your prism about 12 inches in front of your eye and look at a series of trees. You will note that the prism causes an offset in the middle of the trunk of the tree you are looking at. If the offset portion is completely offset from the tree, it is not counted. If any portion of the offset touches the trunk above and below the image, you count it as “in.”

I've included photographs of trees that would be counted in, out and touching (also counted). Plant your foot when you stop, then rotate your body 360 around where you stopped. Count all trees that are “in,” then multiply by 10. Say, you counted 8 trees in, 8 X 10 is 80, and that is the basal area in square feet at that point.

Write the number down, then move to your next location, repeating the process at regular stops. When finished, calculate the average basal area for that stand. Later, you can tell the logger how much timber you want to remove. If your goal is a 70 ft2 stand and the average is 95 ft2, the goal should be to remove enough trees to reach the goal.

Another approach would be to mark trees for removal at each stop to reach your goal, using marking paint. Of course, you can contract with a professional forester, having him mark the stand to the basal area you want for improved forage production.

D+ THINNING

The above procedure works well when you are dealing with established stands of trees of uniform size and composition. However, many times, landowners have numerous areas of much younger and diverse tree species in large densities. It is not uncommon to encounter a young stand of several hundred trees per acre.

Fortunately, these trees are not of commercial size; so, removing the ones you do not want does not involve logging. To the contrary, that is where judicious use of selective herbicides really becomes feasible. Disclaimer: always become certified through your state forestry or wildlife agency to use herbicides! It is not difficult to complete the course material required by most states for private use.

Years ago, we started using the D+ technique to manage stands of trees both for deer and better timber production. Our herbicide of choice has been Triclopyr, which is a chemical designed to control broadleaf and woody plants; and is widely used, either as the single chemical or in mixes.

At last count there were over 200 products containing Triclopyr on the market. It mimics plant growth hormone and causes the plant to literally “grow itself to death.” It can be injected into the tree or more commonly sprayed in a mix of mineral oil or diesel on the outer bark around the base of the tree. Be sure to follow mixing instructions for tree injection that come with the container. Triclopyr is generally thought to be environmentally safe, in that it breaks down quickly in both soil and water.

The D+ method got its name from the procedure of using diameter to regulate which trees are killed in the stand. I personally hate trees in rows, preferring stands that look natural. That makes D+ the perfect solution. Here is how we go about this technique.

Let’s suppose you have a young, dense stand of trees composed of mixed hardwoods, including oaks. To improve the stand, all you must do is walk into it and find a tree that is one you want to keep, say a red oak that is 5 inches in diameter at breast height (4.5 feet). For stands with trees less than 10 inches in diameter, I use the D+10 method. Since the tree is 5 inches in diameter, I add 5+10= 15 and spray the bottom two feet of all trees in a 15 feet. radius of the tree with herbicide (thoroughly wetted). Use a blue dye to help keep track of which trees you spray.

Once you have sprayed all unwanted trees in that radius, go to the next tree you “like” outside it and start the process once more. In this example, let’s say that the next tree is 6 inches in diameter; the active radius would then be 16 ft. When finished, you'll have a stand that will appear natural in tree distribution, plus if you pay attention to diversifying species, an ecologically diverse stand.

For larger trees (10-20 in.), I use a D+20 standard for treatment. Above 20 in., it is better to inject the trees by frilling around the basal diameter with a hatchet and then spraying herbicide into the frills. This often is called “hack and squirt.” If you start with a young stand of trees, treat it to regulate species composition, and then return as the trees grow. It is possible to produce a beautiful and diverse stand of trees that produces forage and mast for your deer, as well as valuable timber for harvest later.

IN CONCLUSION

The math of managing forests by thinning may seem a bit complex at first, yet the principles are simple. The idea is to regulate the density and species of trees to produce deer food, cover and wood products; not to mention a beautiful stand of trees in your deer woods!