Dry and Dry-Mesic Oak-Pine Forest

Buckner (1989) described the pine-hardwood type as a "mid-seral stage that is ephemeral on a given site and is maintained in a changing landscape mosaic where scattered disturbances reinitiate succession in a stochastic manner."  Oak-pine forest types, as such, do not adhere to steady-state dynamics, and more traditional definitions of "old-growth."  White and Lloyd (1998), defined the old-growth oak-pine type as "resembling the transition or understory reinitiation phase of forest development or the mid-to-late phase of plant succession."  They include oak-pine stands that have minimal evidence of postsettlement human disturbance and contain pines exceeding 100 to 125 years old in their definition of old growth (White and Lloyd 1998).

Distribution and Composition of the Dry and Dry-Mesic Oak-Pine Forest Type

Dry and dry mesic oak-pine forests occur along dry ridges and south-facing slopes throughout the southern Appalachians.  By definition, dry and dry mesic oak-pine forests must contain at least 20 percent pine basal area and at least 20 percent oak basal area. The relative dominance of yellow pine species (Virginia, pitch, Table Mountain, and shortleaf) is determined by elevation, exposure, and disturbance regimes.  Scarlet oak and chestnut oak are the most common oak species of this forest type.  Other hardwoods typical of this forest type include: black and white oaks, blackgum, red maple, yellow-poplar, dogwood, sassafras, and sourwood.  Historically, chestnut was a component of the dry and dry-mesic oak-pine type (White and Lloyd 1998).

Although the abundance of the oak-pine type in the Appalachians at the time of European settlement is not clear, use of fire by Native Americans (Buckner 1989, Van Lear and Waldrop 1989), coupled with natural disturbances (wind and ice storms, insects, pathogens, and lightning fire) enhanced and maintained the oak-pine type in presettlement times in the Appalachians.  Native yellow pines (Table Mountain pine, shortleaf, pitch, and Virginia pines) all share some degree of fire tolerance. With increased fire suppression, yellow pines will become less abundant in these forests and, in some cases, oaks will eventually decrease as well (Nowacki and Abrams 1992).  If disturbance regimes are not restored, white-pine, a less fire-tolerant but more shade-tolerant species, may become an important component of old-growth oak-pine forests. Maples, black cherry, and black birch also will increase in the absence of fire. Plant diversity in most dry and dry-mesic oak-pine forests is relatively low, particularlty in the absence of fire when forest understories become dominated by one or two layers of ericaceous species (White and Lloyd 1998).

Structure and Dynamics of Old Growth

Very few studies have documented structural features of old-growth in the southern Appalachians; much of this discussion, therefore, is derived from studies conducted on oak-pine forests in the Piedmont (White and Lloyd 1998) and Interior Highlands (Fountain 1991).  In general, oak-pine forest types exhibit many of the structural features of typical old-growth to some degree.  For example, they have complex vertical structure, patches of different age and size classes caused by continual canopy gap formation, snags and coarse woody debris, and undisturbed soil.  In general however, these features are less pronounced than in more mesophytic hardwood forests (White and Lloyd 1998).

The deviation from the classic old-growth characteristics in oak-pine forests is likely attributable to a more frequent and intense disturbance regime as compared to other forest types.  In general, disturbance regimes in oak-pine forest types create larger patches of mortality than in mesophytic hardwood forests and certain old-growth characteristics can vary greatly among mortality patches.  For example, in a Piedmont oak-pine forest, patches of mortality ranged from 0.5 to 10 acres in size (0.2 - 4.0 ha) and overstory canopy openness in these patches ranged from 60-80 percent.  Most mortality in these patches was pine.  Standing snags and downed coarse woody debris were abundant in these areas, but their presence was temporary and dependent on large but infrequent pulsed inputs (White and Lloyd 1998).

On the other hand, in areas of low-to-medium mortality, amounts of coarse woody debris and canopy gap size (0.06 acre) were similar to values reported for eastern old-growth oak forests.  This information implies that disturbance patterns that predominate in low-to-medium mortality areas are similar to those found in other mature or old-growth forests in the East (White and Lloyd 1998).

Stem diameter distributions in oak-pine forests examined in the Piedmont and Interior Highlands was found to be reverse-J shaped, typical of uneven-aged stands.  However, age and stem distributions of individual species differed among these sites and reflected slightly different disturbance histories.  The pine population on the Interior Highlands site was largely even-agent, a single major disturbance.  At the Piedmont site, the age structure of pines reflected scattered disturbances of sufficient size to result in regeneration of pine and other intolerant species over a period of 200 years (White and Lloyd 1998).

Maintaining the composition and uneven-aged stand structure of oak-pine forests depends on periodic canopy and forest-floor disturbance. Without sufficient disturbance, pines will become minor components of stand composition and structure.  In this sense, old-growth oak-pine may be viewed as ephemeral on a given site, but maintained at a broader landscape scale by disturbances distributed over space and time (White and Lloyd 1998).

See: BROKEN-LINK BROKEN-LINK Standardized Table for Dry and Dry-Mexic Oak-Pine Forests

Information Gaps

White and Lloyd (1998) identified several gaps in our knowledge about old-growth oak-pine forests.  Mostly gaps result from the fact that few of these stands exist and even fewer have been studied.  They recommend:

• Locating, documenting, and describing existing stands and their old-growth characteristics.

• Documenting threatened, endangered, and sensitive plant and animal species that are associated (currently or historically) with this forest type.

• Researching presettlement forest conditions, spatial and temporal scales of nonhuman disturbances, and the distribution of Native American populations and their impact on presettlement landscapes.