Oak – Hickory forests are the most common woodland communities in Frederick County occupying about 70% of the forest land base or an estimated 80,000 acres.  These forests are found on rocky, well drained, upland sites that have acidic soils. Since this kind of terrain is descriptive of much of our forestland, it only stands to reason that this would be the dominant forest association.

Much of our rocky uplands contain oak – hickory forests.

 The tree composition in our oak – hickory forests can display subtle to pronounced differences due to a variety of site factors.  On the drier sites and upper slopes the dominant species may be chestnut, black, and scarlet oak along with pignut and mockernut hickory.  On the lower slopes with deeper soils such species as red and white oak and possibly shagbark and bitternut hickory might join the mixture.  Other trees that are part of these forests include red maple, black birch, black gum, sassafras, beech, white pine, white ash, and tulip poplar.  The understory of the oak – hickory forest typically has dense woody growth composed of species such as red maple, beech, oaks, hickory, black gum, black birch, sassafras, white ash, serviceberry, flowering dogwood, mountain laurel, witch hazel, wild azalea, huckleberry, and blueberry.  The herbaceous ground cover is usually pretty sparse due to the drier conditions and persistent oak leaves that cover the ground. 

Persistent oak leaf cover inhibits herbaceous ground cover in oak dominated forests.

The oak - hickory forest developed as the result of land use practices in the early 1900’s resulting in widespread timbering of forests and large wildfires. Another factor that promoted this type of community was the onset of chestnut blight a disease that wiped out most of the chestnut trees, the most dominant tree found in upland forests at the time.  The result of these factors was that trees such as the oaks and hickories that could withstand forest fires and grow in full to partial sunlight flourished.  An oak-hickory forest is considered to be a sub climax forest community meaning that this species mixture will change if “forest succession” is allowed to progress.  In the absence of major disturbances, the oaks and hickories will become a less dominant part of the forest once shade tolerant species like beech, red maple, black birch; black gum, white pine, and possibly hemlock get established and grow to a dominant position in the main canopy. 

The dominance of oaks and hickories will wane as time passes and a climax forest community develops.

All plant communities undergo change and the oak – hickory forest is no exception.  Various factors are influencing these forests so that oaks may no longer be the dominant species. The typical oak - hickory forest found in the early1980’s usually contained 80% oak in the canopy, and these trees were large enough to be commercially viable.  This forest community was about to witness some profound changes.   The mid to late 1980’s saw the leading edge of the gypsy moth invasion throughout our region. This destructive insect devours oak leaves in the early spring which leaves the tree in a severely weakened condition. Repeated defoliation by gypsy moth during the late 1980’s resulted in significant oak mortality; and, in some cases oaks were nearly eliminated from some sections of forest.  In addition, merchantable oak trees were targeted during selective logging operations which removed oaks and not much else. This type of cutting resulted in an overstory that contained much less oak trees.  In addition, it is unlikely that the moderately shade intolerant oak trees growing in the understory would develop into the main canopy unless they happened to be growing around a significant opening.  The proliferation of deer in our county also impacted oak since deer eagerly feed on small oak seedlings.  Suppressing forest fires became very important for public safety considerations but it had a negative impact on fire dependent plants like oak that benefit from these disturbances.  Finally, the influence of forest succession leading to a tree association dominated by shade tolerant trees like maple, gum, beech, black birch, hemlock, and white pine created conditions unfavorable to oak.  Given all these factors it is reasonable to assume that our future upland forests will contain a smaller percentage of oaks.

Older growth “climax” forests contain species like the beech pictured here.

The oaks that are found in the oak-hickory forests are very important for forest inhabiting wildlife and to the economy.  The acorns that oaks produce in the fall are a winter staple for most of our native wildlife especially deer, turkey, and squirrel.  Oak trees are also highly sought after for lumber and firewood and these species are very important to the local, regional, and national forest products industry.  Due to the importance of oak trees, the science of forestry has developed management practices that can be employed to help ensure that this important species be retained in sufficient numbers where desirable.  Some of these practices include suppressing large gypsy moth populations, engaging in sustainable harvests that target a wide variety of species or create conditions beneficial for oak regeneration, precommercial thinnings that remove competing trees around oaks or other desirable species, tree plantings, prescribed burning operations that mimic the beneficial  effects that fire can have, managing deer numbers so that oaks and other forest vegetation has a chance to grow,   and placing natural or artificial barriers around young oak trees and other vegetation.

Oaks and hickories to a lesser extent are important species for the forest products industry.  This is a photo of a private sawmill located on Catoctin Mountain.