Pine Stand Management

Using pine trees for reforestation has been very popular in Frederick County for more than 50 years. In the 1950’s and 1960’s, there was a real push to plant pine trees on steep, erosive farmland throughout the county, and many of our more established plantations were planted at this time. Residents also planted pines for aesthetic screens around their property, home, driveway, or along the road. In most cases, white pines were used because they grow well in this area, get large, and are long lived. Secondary species like Scotch, red, pitch, Virginia, loblolly, or Austrian pine might be planted alongside the white pine, along with spruce, arborvitae, or Leland cypress. Most of these plantings were conducted at a fairly close spacing of 8’ x 8’ to encourage straight growth, and to provide the necessary screening effect as soon as possible.

Credit: frederick.forestryboard.org - Mike Kay

With the close spacing, it did not take long for the pine canopies to intermingle with their neighbor as they enlarged. The overhead canopy, open understory, and pleasant aroma make young pine stands a pleasure to visit. However, when the pine trees are so closely packed together, their growth and vigor often suffer since they are in intense competition for the available sunlight, water, soil nutrients, and growing space. These competitive forces lower the vigor of the individual tree—and the plantation, as a whole. Pine trees growing at reduced vigor can attract diseases and insects that can cause injury and/or death to individual trees or a large number of trees. One of the most destructive insects that is attracted to dense pine stands is the pine bark beetle. Extended research has shown that bark beetles are attracted to chemicals that are given off by weakened pine trees.

Bark beetle is a generic term for a number of insects that feed on the inner bark of pine trees. In most cases, the adult will lay eggs under the bark of the host tree in the fall or early spring. The eggs will hatch, and the young larvae will feed on the inner bark of the tree, often creating elaborate galleries underneath the bark. Intense feeding activity will girdle all or parts of the tree, which will cause sections of the tree to wilt and die. It is more difficult to control bark beetles once they are inside a pine tree. Often the only option is to cut the infested tree down and remove it from the area.

One way to easily determine if a tree or stand of trees is susceptible to attack by pine bark beetles or other insects is to observe the amount of green growth along the total height of the tree, also known as the “live crown ratio” of the tree. For example, if a pine tree is 100’ tall, and it has green growth along 50’ of the total height, it has a live crown ratio of 50%. A white pine tree is usually healthy if it has a live crown ratio of 40% or more. So, if you walk through your pine stand and observe an average live crown ratio of 30%, it tells you that these trees are not healthy and could be prone to bark beetle attack.

The best way to keep your pine plantation healthy is to periodically thin out trees before the stand becomes too dense. This thinning should begin fairly early in the life of the plantation when the canopies begin to close together, and continue at about 15 year cycles. These thinning can involve single trees, groups of trees, or entire rows of trees, depending on the size of the plantation and your particular objectives. These thinnings may be noncommercial (meaning that you have to do it yourself or pay someone to do it).

Article by FCFCDB

Nature note for 11/12/21

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