Tuesday, December 13, 2016

Creating Healthy Woods and Improved Deer Habitat through Forest Thinning

Forest owners have many reasons for owning their property. This may include things like improving timber production, creating wildlife habitat, protecting water quality, enhancing recreational opportunities, and many others. If your reasons include creating healthy woods and improving deer habitat, a thinning may be the right forest management practice for your woods.

This stand would benefit from a thinning. The trees are
overcrowded and there is little growth in the
 understory besides fern.

Forest thinnings are conducted in overcrowded stands when they are still relatively young, from 15 to 50 years of age however, thinning can benefit older woods. By design, thinning reduces competition among neighboring trees. Foresters thin trees to improve growth rates and overall tree vigor. Wildlife biologists thin trees to improve wildlife habitat by increasing understory growth and mast (acorns and nuts) production.

Thinning frees desirable trees from neighboring trees competing for growing space. Trees need room to grow and expand their crowns. If they are too close, they compete for resources, primarily light. The focus is on improving growing conditions for selected crop trees by removing competing poor quality and less desirable species. The trees left are evenly spaced, released, and encouraged to grow.

Trees compete for light. To grow, they need room 
to expand their crowns.
Most stands of trees originally have thousands of seedlings and sprouts per acre. As they grow, competition for light, water, and nutrients increases. The most vigorous trees become the dominant and co-dominant trees in the stand - their crowns are above or make up the main canopy level. The less vigorous trees are crowded by their neighbors; their crowns become misshapen and restricted. These trees become the intermediate and suppressed trees in the canopy - their crowns are below the main level of the canopy, receiving little light from above. Of the thousands of seedlings beginning life in a forest, less than 100 per acre may survive and thrive to become a mature forest. 

Forest thinning provides the opportunity to select and encourage the dominant and co-dominant trees you want, those that meet your objectives. These trees can provide for future timber production, wildlife habitat or myriad other values. For example, thinning around an oak tree will improve its growth rate and vigor and may very well increase the amount of acorns it produces.

Trees selected to leave are marked with flagging
or paint prior to any cutting occurring.

Improved deer habitat is an added wildlife benefit of thinning. Deer are browsers, tree and shrub twigs, buds, and leaves make up a primary component of their diet. A deer’s system can easily digest woody browse. They will feed on it year round. Browse is the most important source of deer nutrition in forested environments. During winter and early spring it is a vital source of nutrition as most other food sources are unavailable.

Thinning trees in winter puts tops on the ground that deer can browse during lean times. Once the tree hits the ground, deer have access to the tender buds and twigs on the top of the tree, which are generally nipped off within weeks. Thinning overcrowded trees also increases the amount of sunlight reaching the forest floor. The increased sunlight provides ideal conditions for new seedlings and herbaceous plants to get started, providing food and cover for deer as well as other wildlife.

Winter and early spring thinning provides deer
browse during a critical time of year.

In addition, hardwood tree stumps often re-sprout after cutting. Stump sprouts provide additional woody browse for deer. Sprouts may remain within the reach of deer for years, providing a valuable food source. Some deer habitat managers recommend hinge cutting trees during thinning operations. Hinge cut trees are cut half-way through allowing the tree to fall to the ground. The “hinge” keeps the tree alive to continue producing leaves and vertical shoots.

Red maple stump sprouts provide deer
with a source of woody browse.

This hinge cut ash is producing stump sprouts
and sprouts along the stem as browse.
Thinning operations can be either commercial or non-commercial, depending on the products being removed and available markets. Often thinning provides no immediate return beyond improved wildlife habitat. In small diameter stands, where there are few markets for pulpwood and/or firewood, landowners may do the work themselves or pay a contractor to cut trees. A commercial thinning provides an income opportunity as the landowner sells the trees being removed. Commercial thinning generally occurs later in stand development when trees removed have reached small sawlog size or is in an area where good markets for pulpwood exist. 

In a thinning, the most important decision is selecting which trees to keep for the future. Focus on the value of the future forest and leave trees that meet your ownership objectives. No matter what you manage for, leaving trees with the highest potential future value is important. Remember, in many cases trees that are good for wildlife are also good timber trees.

This young hardwood stand was thinned pre-commercially.
A professional forester or wildlife biologist is an important ally when designing a thinning treatment. Some landowners choose to work directly with a logging contractor who buys timber; however, these individuals may not have the training and experience to implement a proper thinning. If you choose to do most of the planning on your own, it is advisable to use a forester to conduct any timber sale, including a thinning, as they have knowledge of markets and buyers and can ensure the practice improves the overall well-being of your woods.

This stand of yellow poplar could be thinned commercially.

Unlike regeneration harvests, thinning does not result in large canopy openings. The gaps created between crop trees are small enough that remaining crowns expand and close back together over time. Therefore, it is important to have the proper spacing among crop trees. If the openings are too large, tree replacement from regeneration (seedlings and sprouts) will be necessary. In addition, the light reaching the forest floor might initiate competitive plants or encourage invasive species establishment including invasive exotic trees, shrubs, vines, and grasses. It is important to monitor any harvested area for undesirable vegetation and control it before it gets out of hand.

Thinned the previous growing season, this white pine stand 
shows a flush of new herbaceous growth and stump sprouts.
In many areas deer populations exceed the habitat carrying capacity and over-browsing is common. If sprout growth is browsed completely to the stump consider reducing deer numbers. Implementing additional management practices that improve habitat is also desirable.

Sprouts heavily browsed down to the stump, like this black gum, 
may be an indicator of too many deer for the available habitat.
A well designed thinning should put your wooded land well on its way to meeting your objectives of improved forest health and wildlife habitat. A successful thinning involves planning, implementation, and monitoring. The end result is more valuable timber, a vigorous, healthy forest, and improved habitat for wildlife.

For additional information on thinning see:

- Forest Thinning: A Landowner’s Tool forHealthy Woods, University of Maryland Extension

- Intermediate Cuttings in Forest Management, University of Wisconsin Extension

- Create Living Thicket Cover by Hinge-Cutting, Quality Deer Management Association

By David R. Jackson
Penn State Extension

No comments: