By
Dave Jackson, Forest Resources Educator, Penn State Extension
BELLEFONTE,
PA--Many factors affect our ability to successfully regenerate and sustain forests.
Competing vegetation, high deer impact, and light reaching the forest floor,
referred to as C-D-L. Successful forest regeneration depends on addressing
these three main factors. Joe Harding, the Penn State Forest Land Management
Director, considers each factor when examining a forest stand. His prescription
for treatment depends upon what he wants to accomplish and the problems he sees.
The prescription then guides the management of the area. Joe explains, “If woodland
owners follow this simple formula, C-D-L, they can be successful in managing
their forests.”
Competing
vegetation interferes with the establishment and growth of desirable
regeneration - seedlings and sprouts. Common problem plants are beech, striped
maple, eastern hophornbeam, hayscented fern, and numerous invasive plants; however,
there are many others that can be problematic. The abundance of these
undesirable plants has increased over time for a couple of reasons. First, they are low
on the deer browse preference list. 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 well in shady understory conditions. They are
often well established in mature forests.
Like
weeding a garden, controlling interfering plants is imperative to successfully
regenerate hardwood forests. Control measures can include several options. Competing
trees and shrubs can simply be cut; however, this often results in the plant re-sprouting.
Successful control is most often achieved using herbicides labeled for brush
control in forests. Researchers have studied different active ingredients,
rates, and time of year to develop safe and effective application prescriptions
to control competing and invasive plant problems. Certified applicators are available
to make herbicide applications for woodland owners.
Deer
browsing impacts forest regeneration in several ways. When deer densities
exceed habitat carrying capacity, deer impact the ability of forests to
regenerate desirable tree species. Selective deer browsing reduces seedling numbers,
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 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.
It
is essential to control deer populations to maintain a balance with habitat
conditions. Until that balance is reached it may be necessary to exclude deer
from areas, using deer exclusion fences, for years until desired regeneration
is above the deer’s reach. For example, erecting an eight-foot woven wire fence
around a cutting unit may be the best option to control high deer impact. In
addition to fencing, landowners may consider using the Deer Management Assistance
Program or DMAP. DMAP allows landowners to harvest additional antlerless deer on
their property during regular hunting seasons.
Lastly, it is necessary to understand the light
requirements of desired regeneration. Most desirable timber species such as
black cherry, white ash, yellow poplar, hickory, and black walnut are intolerant
of shade, meaning they grow
best in full sunlight. All oak species are intermediate in shade tolerance; they
grow well in the middle ranges of light availability. Sugar maple, basswood,
and hemlock are shade tolerant; they can compete well in fully shaded
conditions.
The
tree species you are managing for dictate the type of regeneration harvests recommended.
When managing for shade intolerant trees, species with high light requirements,
practices that let large amounts of sunlight to the forest floor are preferred.
These practices include clearcuts (ONLY if advance regeneration is present or
for species like aspen that regenerate from root sprouts), shelterwood harvests,
and seed tree cuts. Selectively harvesting individual mature trees from the
forest canopy allows only 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 - planning, money, and time. Failing to address
all three components, competing vegetation, deer, and light, can lead to
inadequate desirable regeneration and unsustainable conditions. In summary, if competing
vegetation is controlled, deer impact is kept low, and the light tolerances of
the desired tree species are taken into consideration, you will likely be
successful in establishing and sustaining new forests.
For more on C-D-L practices, see the Penn State
Extension Forest Science Fact Sheet entitled: Regenerating Hardwood Forests:
Managing Competing Plants, Deer, and Light. It can be found online at: https://extension.psu.edu/regenerating-hardwood-forests-managing-competing-plants-deer-and-light
