Southern Piedmont Moist Forest

This system encompasses mixed deciduous hardwood or occasionally hardwood-pine forests of mesic sites in the Piedmont of the southeastern United States. Most examples occur on lower or north-facing slopes where topography creates mesic moisture conditions. A mix of a small number of mesophytic trees is usually dominant, with Fagus grandifolia most prominent. Both acidic and basic substrates are currently included in this concept, as are certain heath bluffs, where dense shrub layers of mesophytic ericaceous shrubs may occur beneath an open tree canopy. Fire is naturally infrequent in this system, due to the slopes and moist conditions. If fire does penetrate, it is likely to be low in intensity and may not have significant ecological effects. Vegetation consists of forests dominated by combinations of trees that include a significant component of mesophytic species. Fagus grandifolia is almost always abundant and is often strongly dominant. Quercus rubra, Liriodendron tulipifera, and Acer rubrum may be abundant. In basic soil examples, Fraxinus americana and Acer floridanum are also abundant. A well-developed understory is usually present. Herbs range from fairly dense in basic examples to sparse in acidic examples, and may be nearly absent in a few. The composition of all lower strata varies substantially with soil acidity.

These forests are dominated by mesophytic tree species. Fagus grandifolia is almost always abundant and is often strongly dominant. Quercus rubra, Liriodendron tulipifera, and Acer rubrum may be abundant. In examples on basic soils, Fraxinus americana and Acer floridanum (= Acer barbatum) are also abundant. A well-developed understory is usually present. Shrubs are generally sparse to moderate in density, except on heath bluffs. Herbs range from fairly dense in basic examples to sparse in acidic examples. The composition of all lower strata varies substantially with soil acidity. Basic examples have fairly diverse plants, especially herbs, which may include a number of species shared with Southern and Central Appalachian Cove Forest (CES202.373). The more common acidic examples have fewer plant species, though generally they have a higher species richness than other drier ecological systems.

Examples occur on lower slopes or on north-facing slopes, where topography creates mesic moisture conditions. This system may occur on any kind of rock type, with rock chemistry being an important determinant of variation. Most soils are acidic, but those formed on mafic rocks often are circumneutral to basic. The moist conditions and slope limit natural fire intensity and frequency.

Fire is naturally infrequent in this system, due to the slopes and moist conditions. If fire does occur, it is likely to be low in intensity and may not have significant ecological effects. These forests generally exist naturally as old-growth forests, with canopy dynamics dominated by gap-phase regeneration. Small to occasional medium-sized canopy gaps created by wind are likely the primary form of natural disturbance, though infrequent fires might create gaps. Most of the prevailing species are shade-tolerant. Most are not very fire-tolerant. The mesophytic forest type is fire regime class III, surface fires with return intervals of 20 to 70 years (Landfire 2007a). Mixed-severity fires may occur approximately every 100 years depending on climatic conditions. Disturbance may also occur by recurrent, severe insect defoliations or droughts. Ice, straight-line winds or microbursts may cause blow-downs on a scale of 1 to 10 acres. Stand-replacement fires happen very infrequently. Low-intensity surface fires, whether natural or set by Native Americans, would have maintained the more fire-resistant Castanea dentata and oak species.

Conversion of this type has primarily resulted from repeated canopy removal through logging, which is also the most critical anthropogenic threat. These sites were historically less frequently logged than the adjacent pine-dominated uplands, with more desirable species being removed in preference to Fagus grandifolia, which is less desirable in the lumber trade. In addition, some mesic hardwood forests in more moderately dissected terrain have been converted to pine plantations or impacted (destroyed or fragmented) by agriculture. Bluff habitats are often prime sites for development, especially along major rivers. Complete devastation by natural agents was probably very rare in this forest type (Batista and Platt 1997). These forests also suffer the effects of ozone and acidic atmospheric deposition.

Aside from actual site conversion, feral hogs represent one of the greatest threats to biodiversity in these forests (Engeman et al. 2007). They can be especially difficult to control in sensitive slope forests (Edwards et al. 2013). In addition, invasive exotic species including Elaeagnus umbellata, Hedera helix, Ligustrum sinense, Lonicera japonica, and Wisteria sinensis can become dominant in the ground and shrub layers following canopy disturbance (Edwards et al. 2013). For mesic hardwood forests containing Fraxinus species, emerald ash borer (recently found in Georgia) may also be a significant stressor.

The most significant potential climate change effects over the next 50 years include periods of drought, which has affected parts of the coastal plain. Droughts will affect the health and survival of the moisture-requiring trees, as well as increase the probability of damaging wildfire.

This ecological system ranges throughout the southern Piedmont, from Virginia to Alabama.