C-D-L: An acronym for successfully regenerating hardwood forests



For The Express

BELLEFONTE– Many factors affect our ability to successfully regenerate and sustain forests. Competing vegetation, high deer impact, and sufficient light to the forest floor, referred to as C-D-L, are three main factors that woodland owners have to contend with to successfully regenerate forests. Joe Harding, the Penn State Forest Land Management Director, takes these three factors into consideration each time he examines a forest stand. His prescriptions for treatment are based on what he wants to accomplish and the kinds of problems he sees. The prescriptions then become a guide for managing that area. Joe explains, “If woodland owners follow this simple formula, C-D-L, they can be successful in managing their forests.”

Competing vegetation consists of plants that interfere with the establishment and growth of desirable regeneration, seedlings and sprouts. It can consist of any number of species including, but not limited to, beech, striped maple, eastern hophornbeam, hayscented fern, and numerous invasive plants. The abundance of these undesirable species has increased for a couple of reasons. First, they are low on the browse preference list for deer. Where deer impact is high, these less-preferred browse species can dominate forest understories. Second, many of these species are tolerant of shade and grow in shady understory conditions, so most are well established in mature forests.

Like weeding a garden to grow a crop, controlling interfering plants is imperative to successfully regenerate hardwood forests. Control measures can include several different options. Competing trees and shrubs can simply be cut down. However, this often results in the undesirable species resprouting. Successful control is most often achieved through a targeted application of herbicides labeled for brush control in forests. An enormous amount of research has been done looking at different active ingredients, rates, and time of year to come up with the application prescriptions we use today to control competing and invasive plant problems. Certified applicators are available to make herbicide applications for woodland owners.

Deer browsing has several effects on forest regeneration. When deer densities exceed the carrying capacity of the habitat, they impact the ability of forests to regenerate desirable species. The number of seedlings is reduced, surviving seedlings are smaller, and the species composition is shifted to less preferred species, i.e., species deer don’t like to eat. Unfortunately, desirable timber species such as the maple, oak, hickory, and yellow poplar are high on the food preference list and can be completely browsed out of forest understories when deer impact is high.

Deer populations must be controlled to keep them in balance with their habitat. Until that balance is reached it may be necessary to exclude deer from areas, using deer exclusion fences, for years until the regeneration is above the deer’s reach. For example, erecting an eight-foot woven wire fence around the perimeter of a cutting unit may be the best option to control high deer impact. In addition to fencing landowners can take advantage of the Deer Management Assistance Program or DMAP. DMAP is a program offered by the PA Game Commission which allows landowners to harvest additional antlerless deer off their property during the regular hunting seasons.

Lastly, light tolerances of desired species need to be considered when trying to regenerate forests. Most desirable timber species such as black cherry, white ash, yellow poplar, hickory, and black walnut are classified as intolerant of shade and all oak species are classified as intermediate in shade tolerance. Sugar maple, basswood, and hemlock are desirable timber species that will regenerate in shaded understories.

The species of trees you are managing for dictate the type of regeneration harvests recommended. When managing for species with high light requirements, practices that let large amounts of sunlight to the forest floor are preferred. This includes regeneration harvests known as clearcuts (if advanced regeneration is present), shelterwood harvests, and seed tree cuts. Selectively harvesting individual mature trees out of the forest canopy allows small amounts of light to reach the forest floor and will likely result in the regeneration of shade tolerant species.

C-D-L certainly involves investments of thought, money, and time. Failing to address all three components, competing vegetation, deer, and light, could lead to inadequate desirable regeneration and unsustainable conditions. In summary, if competing vegetation is controlled, deer impact is reduced, and the light tolerances of the desired species are taken into consideration you will be successful in establishing and sustaining new forests.


Dave Jackson is Forest Resources Educator at Penn State Extension. He can be reached at (814-355-4897 or drj11@psu.edu)