Forest Thinning Techniques for Wildlife Habitat

While the white oak (Quercus alba) thrives in the eastern half of the country, other members of the Quercus genus can be found throughout the United States. They include the post oak (Q. stellata), chinquapin oak (Q. muehlenbergii), swamp white oak (Q. bicolor), and Oregon oak (Q. garryana), and are vital to wildlife wherever they grow.

Saville added that landowners shouldn’t leave only white oaks as part of a crop tree release effort. The most productive stands (a forestry term for a collection of trees) include a wide variety of mast producers. That way, if one species fails to drop its bounty one year, others can supply crucial nutrition to wildlife.

To begin a crop tree release project, first mark which trees to keep and which ones to remove. Toward that goal, McCarthy and Saville walked through a section of our forest and put two orange ribbons around each tree to be kept and just one ribbon around each tree to be removed. While deciding which trees to save and cut, they also considered which way neighboring trees would likely fall when leveled. It does no good to keep a tree when a nearby undesirable one is likely to crash into it once the sawing begins.

Elaine and I found it illuminating to watch this process. For example, we never realized we had a native American crabapple (Pyrus coronaria) growing on our land. Some red maples (Acer rubrum), red cedars (Juniperus virginiana), and yellow poplars (Liriodendron tulipifera) had enclosed it to the point that it never received enough sunlight to produce fruit. That will change now.

The two foresters also marked a number of scarlet oaks (Q. coccinea) and even a few white oaks to remove. The scarlet oaks were chosen because they have one of the shortest life spans in the red oak family, and they’re considerably more prone to disease. One scarlet oak, though healthy, was removed because it was growing between two stout white oaks, which will now thrive.

Even widely cherished white oaks should be leveled if they’re competing with a nearby family member or a soft mast tree. Malformed white oaks are also a candidate for removal, as are similarly afflicted trees of any species. Again, tree health and diversity in any woodlot is crucial.

After the selected trees had been cut, it was fascinating to see how different this section of our woodlot looked and what the decision-making process had been. For instance, McCarthy and Saville left a black locust (Robinia pseudoacacia), which we would’ve cut for firewood, because it’s an excellent pollinator. It’s also a superb nitrogen-fixer, and it enriches the soil. Black cherry (Prunus serotina) and sourwood (Oxydendrum arboreum) are other great pollinators, and we were encouraged to save those trees during future crop tree release projects.

Several small dogwoods (Cornus florida) also survived the crop tree release process. Dogwoods do best as understory trees, so we left a few to grow under white oaks. Although the trees’ red drupes aren’t edible for humans, many species of wildlife enjoy them, from deer to songbirds. Among the other trees we left in place were a scarlet oak, because it was fairly large and healthy; a black gum (Nyssa sylvatica), which is a soft mast producer; a mockernut hickory (Carya tomentosa), since squirrels relish the nuts; and a post oak. Often-removed trees that we decided to take out included red cedars, red maples, green ashes (Fraxinus pennsylvanica), and white ashes (F. americana). Ashes are dying across much of the country, because of the emerald ash borer infestation.

Finally, though white oak family members are prized, a diverse woodlot should also include red oak species, such as Northern red oak (Q. rubra), pin oak (Q. palustris), black oak (Q. velutina), and blackjack oak (Q. marilandica). If the white oak crop fails, the red oak species can still supply valuable hard mast.

Hinge Cutting

While crop tree release is certainly one of the most important acts for improving a habitat, there are a few other projects that also offer plenty of benefits. Hinge cutting is a great way to create more ground cover and food for wildlife of all kinds. Begin by selecting a tree 3 to 8 inches in diameter at waist height. Many land managers prefer maples for this process, particularly red maples, but I’ve also hinge-cut redbuds and red cedars. Red cedars can add a lot of ground cover, because they’re bushy evergreens. McCarthy agrees that red maples are a good choice for hinge cutting.

“Since they are very shade-tolerant, red maples can take over a woodlot, and also have less commercial value than many trees,” McCarthy said. “Their leaves, though, are a favorite food of deer, so hinge-cutting maples is a good way to maximize their benefit. And after they are hinge-cut, red and other maples provide valuable ground cover for small mammals and songbirds.”

After selection, the next step is to cut about 75 percent of the way through a tree so the partially severed part remains attached to the base while allowing the tree to be bent over parallel to the ground. Thus, the parallel part is still able to receive nutrients while wildlife can now feed on the tree’s leaves or seeds and find cover among its branches.

McCarthy said he recommends using a handsaw for hinge cutting, because it needs to be done slowly. I’ve used chainsaws successfully, but I’ve also had times when they cut too much, too fast, and too deeply, killing the tree as a result. Good candidates for hinge cutting include trees growing along the edges of food plots, on field borders, along seeded logging roads, and in any spot without ground cover.

Small Clear-Cuts

Small clear-cuts are another project McCarthy and Saville encourage landowners to have done in their woodlots. Clear cutting is the practice of cutting all the trees in one area at the same time. A decade or so ago, I arranged to have a trio of clear-cuts consisting of 1 to 5 acres done in the back of our property.

“The clear-cuts added not only diversity of habitat to your land, but also a way to manage many species of trees for wildlife,” McCarthy said. “You probably have a lot more species of songbirds, for example, now.”

McCarthy’s analysis was spot on, because we now have young forest birds, such as yellow-breasted chats, white-eyed vireos, and brown thrashers. Migrating woodcocks also stop in during early spring every year. The newly emerged wild blackberry, raspberry, and wineberry bushes in the clear-cut areas provide valuable soft mast for wildlife, and plenty of berry pies and cobblers for us. I’ve even found wild turkey nests in our berry thickets.

I’ve also created several additional small clear-cuts throughout our land. All I do is select a 15-by-15-yard patch and level every tree except a few mast producers. The resulting tangles of explosive growth become wildlife oases in a year or two.

Girdling

Girdling large trees is a great way to slowly kill them without potentially damaging nearby trees. Girdling involves making parallel horizontal cuts several inches apart. The cuts should go fairly deep into the cambium layer.

“The effect is to starve the roots of the photosynthetic products,” McCarthy said. “Girdling actually severs the phloem connection, which is responsible for movement from crown down to the roots. This explains why many trees will appear to be alive for several years after being girdled. The roots are still feeding the crown through the xylem with the last of the root stores, while all along the roots are gradually reduced by the lack of feeding from the crown. The roots go first, then crown losses follow, then, ultimately, mortality.”

An advantage of girdling is that cavity nesters, such as woodpeckers, wood ducks, bluebirds, and tufted titmice, will benefit greatly, as will songbirds that feed on the insects attracted to the dying tree.

I’ve often girdled ashes and yellow poplars, but Saville convinced me not to do so anymore. “Ashes and yellow poplars can develop very brittle tops when they start to die,” he said. “So when it comes time to finish cutting them, doing so could be very hazardous.”

Hack-and-Squirt

“Hack-and-squirt” is another valuable technique for landowners when thinning a woodlot, and it’s a great way to make den sites as well as kill trees that might harm others if they fall the wrong way. For this project, use hatchets, machetes, tomahawks, or axes. At chest level, make chops in the trunk so you form a series of circling cuts. Be sure to cut deeply enough that you penetrate the cambium layer, creating a cuplike incision. Lastly, squirt an herbicide into the incision. Adding a surfactant, which is a liquid substance that helps carry the herbicide to its target, can make the treatment more effective.

While visiting our land, McCarthy quickly located two trees that proved to be ideal candidates for hack-and-squirt. A large red maple was shading several young white oaks and a pignut hickory (Carya glabra). Felling the maple would likely cause damage to one of those hard mast producers. The second was a large Virginia pine (Pinus virginiana) that towered over some young oaks growing in close proximity.

“Eventually, the red maple and Virginia pine will become stick skeletons of themselves, feeding areas for many species of woodpeckers, and potential nesting sites for songbirds that require cavities to lay their eggs,” McCarthy said. “And you’ve daylighted a half-dozen hard mast producers without any damage to them.”

Eliminating Invasive Plants

One of the most daunting challenges facing America’s rural landowners is the proliferation of invasive plants. Some of the worst are multiflora rose (Rosa multiflora), autumn olive (Elaeagnus umbellata), English ivy (Hedera helix), Japanese honeysuckle (Lonicera japonica), Japanese barberry (Berberis thunbergii), Asiatic bittersweet (Celastrus orbiculatus), common privet (Ligustrum vulgare), and Ailanthus altissima (also known as “paradise tree” or “tree of heaven”).

I’ve dispatched all the Ailanthus and English ivy on my land, but I told McCarthy that I seemed to be losing the battle to the sharp-thorned multiflora rose, and barely holding my own against the autumn olive. The rapidly spreading Asiatic bittersweet had also recently appeared. The management procedure I’ve been using is called “cut-and-squirt”–that is to cleanly cut the offending plant at ground level and then squirt the base with an herbicide.

McCarthy believes this version of cut-and-squirt is a viable approach, but for particularly hardy invasive plants, he offered this suggestion: “For multiflora rose, for example, try using a handsaw to make rough cuts instead of smooth ones,” he said. “The rougher cuts allow more surface area to be exposed to a chemical, so the plant absorbs more of the herbicide. Also, try to find the dominant stem, because it will send the herbicide to the entire plant, especially to the roots.”

Managing a woodlot is a never-ending job, but the rewards of creating better wildlife habitat and a healthier forest are worth the effort.

Bruce Ingram is a freelance writer and photographer, and the author of 10 books, including Living the Locavore Lifestyle, a book on living off the land.