FW404: McComb Ch7, Dickinson CH2 and CH4
McComb Ch7
Disturbance Fundamentals
Disturbances include fires, hurricanes, volcanoes, floods, and earthquakes.
In the United States, average impacts per year include:
burned
affected by hurricanes
affected by insects and pathogens
Economic cost to society is over 1{,}000{,}000{,}000\ \$\$ per year (Dale et al. 2001).
Disturbances are not only catastrophes; they can renew habitat for other species: e.g., wind adds dead wood, fires open canopy and initiate new forests, floods create seedbeds for willows and cottonwoods.
Biodiversity conservation often depends on disturbance; hence understanding disturbances helps in managing habitat and designing silvicultural systems that support forest-associated wildlife (Franklin et al. 2002).
Key disturbance characteristics used to predict effects on forest development and habitat elements:
Type of disturbance
Size and pattern
Frequency
Severity
Disturbance type matters: different causes (e.g., fire vs. wind) produce different habitat-element changes.
Estimating disturbance characteristics supports prediction of forest recovery and subsequent vegetation structure.
Disturbance Size, Pattern, and Frequency
Disturbances vary in size; size influences species that remain or recolonize after disturbance (Rosenberg & Raphael 1986).
Example: 3 million ha burned in 2002 in the U.S.; Biscuit Fire alone was ~2.0\times 10^{5}\ \mathrm{ha} in southern Oregon; many fires are much smaller.
Disturbance size distributions are typically skewed: many small disturbances and fewer large disturbances (Figure 7.1 shows a histogram of fire size across 2898 lightning fires 1980–1993; data are on a logarithmic scale).
Disturbance size relationships with species responses:
Large, severe fires: black-backed woodpeckers, elk, bison colonize forests; large quantities of dead trees and forage become available (Figure 7.2).
Very small openings (e.g., 0.1 ha): white-footed mice favored; larger openings decrease white-footed mice abundance; deer mice higher in larger openings (Buckner & Shure 1985).
Disturbances can facilitate establishment of invasive species; persistence depends on disturbance regime (Hobbs & Huenneke 1992; Blair et al. 2010).
Disturbance size also influences animal home ranges and displacement risk (see displacement considerations in next section).
Disturbance Pattern (Spatial Arrangement)
Pattern refers to the spatial arrangement of disturbance patches (clumped, random, or uniform);
Clumped, fine-scale disturbances (e.g., pockets of root-rot) may cumulatively reduce habitat within an individual’s home range.
More random or uniform disturbance distributions may allow tolerance, as only a portion of any given home range is affected.
Edge effects (topic to Chapter 16) influence how openings function; circles have the least edge per unit area, so two 100 ha disturbances with different shapes (circular vs amoeba) can function differently for habitat elements (edge availability, microclimate, species responses).
Disturbance pattern interacts with size to shape resource distribution within and among home ranges for species.
Disturbance Severity and Biological Legacies
Severity assesses the impact on the stand: is the stand completely replaced or only partially opened with increased growing space for survivors?
Severity determines how much organic material is destroyed or redistributed and the form of material remaining (living vs. dead).
Severe disturbances (e.g., crown fires, volcanoes) can leave substantial biological legacies:
Even after severe events like Mount St. Helens, seeds, fungi, and animals may persist below ground or in protected pockets, enabling recolonization and trajectories toward a new forest (Nash 2010).
Legacies from disturbances provide habitat elements for later succession (e.g., legacy trees, snags, logs) and can seed new stands and inoculate with mycorrhizal fungi (Dahlberg 2001).
Examples of legacies contributing to habitat elements:
Snags and logs provide structure for wildlife and substrates for regeneration.
Regrowth and residual structures may persist into subsequent stands and provide habitat for later stages (McComb & Lindenmayer 1999).
In northern forests, biological legacies such as large old trees used for nesting by species like the northern spotted owl demonstrate long-term habitat value of legacies (North et al. 1996).
Disturbance Frequency and Return Interval
Frequency influences tree species composition, amounts of living and dead organic material, and the trajectory of stand development.
Hurricanes, for example, influence the proportion of large areas in early vs. late stages of development (Figure 7.4).
Return interval (time between disturbances) is a common way to characterize frequency. It varies by disturbance type and forest type:
Fire: as frequent as once every 2\ ext{–}5\text{ years}3\times 10^{2}\text{–}4\times 10^{2}\ \text{years} in northwestern coniferous forests
Disturbance frequency in managed forests differs from natural intervals; large deviations can increase the risk of losing habitat elements and the species that depend on them (Hansen et al. 1991).
Operational implication: managing disturbance frequency, size, and severity with silvicultural practices can help balance habitat elements, water, and timber values.
Disturbance Size vs. Habitat Scale and Edge Effects
A hypothetical 1000 ha forest, uniformly old and unmanaged:
Small-scale disturbances occur many times per year with small openings (e.g., 0.1 ha) and low severity.
Large-scale stand-replacing disturbances (e.g., hurricanes) may occur about once per 100 years, affecting the entire stand.
General pattern: frequent small disturbances are typically low in severity; large severe disturbances are infrequent.
If managers prevent disturbances too frequently, when a disturbance does occur it may be unusually large and intense due to fuel accumulation and suppressed natural disturbance regimes. This highlights the importance of balancing disturbance frequency, size, and severity in forest management to maintain habitat elements and ecosystem services.
Stand Development and Succession Concepts
Early ecological perspectives framed vegetation change after stand-replacement disturbances as ecological succession; later research shows recovery is not fully deterministic but follows general patterns.
Forest development is a continuum typically broken into four physiognomic stages (Oliver 1981, Oliver & Larson 1990):
1) Stand initiation
2) Stem exclusion
3) Understory reinitiation
4) Old growth (shifting gap phase)The sequence and timing of these stages depend on disturbance severity and frequency and on regeneration potential.
Basal area (BA) concept:
Basal area is the cross-sectional area of all trees on a stand per unit land area (often per hectare). It can be estimated by summing cross-sectional areas of all trees at breast height (1.4 m). The maximum basal area a site can support depends on moisture, growing-season length, species, nutrients, etc.
Basal area helps quantify stocking and competition; higher BA means more competition and different growth dynamics.
A commonly used explanatory diagram shows that in a 1000 ha stand, different patterns of stocking can give the same BA but with different tree densities (i.e., many small trees vs. few large trees).
The transition from stand initiation to stem exclusion triggers competitive stratification into crown classes:
Dominant: receive light from above and sides; deep crowns; high leaf area; rapid growth
Codominant: receive light from above; large portion of canopy but not as dominants
Intermediate: smaller crowns; slower growth; contribute less to upper canopy
Suppressed: very small crowns; light/moisture limitations; often die
Wolf trees: legacy trees from the previous stand with unusually deep crowns due to open-grown conditions during stand initiation
Early stand development in eastern hardwoods can see 90–99% die, especially among smaller stems, with most energy now directed to decomposition in a detrital-based system; dead wood produced is often small and decays quickly, unless large trees die later in stand development.
As a stand matures, competition reduces, leading to uniform canopy and reduced forage availability beneath the canopy.
Understory Reinitiation and Gap Dynamics
As crown differentiation continues and some larger trees die, canopy gaps form allowing sunlight to reach the forest floor.
Shade-tolerant understory plants can establish; regeneration can occur from nearby gaps or from seedbanks stored in soil; initial energy resources for forage return, though often limited.
Dead wood abundance becomes low in this stage; some large snags/logs begin to form due to ongoing disturbance, competition, and insect/disease activity.
Regeneration in gaps eventually replaces dominant trees, leading to a new stand structure; this transition marks understory reinitiation.
Old Growth and Shifting Gap Phase
Regeneration eventually replaces older dominants and codominants, initiating old-growth or shifting gap phase with higher structural complexity.
The stand accumulates large pieces of dead wood, trees of multiple sizes and species, greater vertical and horizontal diversity, and more complex patchiness.
Forage patches develop, though total forage may fluctuate with growth rates and disturbance history.
In some forests, frequent low-severity fires maintain a level of gapiness that sustains forage availability for certain species (Figure 7.7).
Shade effects on plant chemistry: regenerating plants in partial shade may have different defensive chemistry than those in full sun; e.g., shade-grown seedlings may have different defensive compounds than clear-cut conditions (Tucker et al. 1976; Happe et al. 1990).
Habitat Elements Through Time: Curves and Pathways
Some habitat elements follow a U-shaped pattern (Curve 1): dead wood, horizontal complexity, plant and animal diversity, edge presence – high immediately after disturbance, decline as crowns close, then increase again with gap formation and later decay of dense stands.
Other elements follow a sigmoidal pattern (Curve 2): diversity of tree sizes, vertical complexity, mean tree size, incidence of damaged/hollow trees, leaf litter depth, bark surface area, and live biomass – gradually increasing from stand initiation through old growth.
In many forest types, Curve 2 may reflect shifts in dominance by shade-tolerant species over time.
Spies (1998) provides generalized patterns for Douglas-fir forests (Figure 7.8):
Curve 1: dead wood, horizontal diversity, species diversity, and edges rise after disturbance, fall as crowns close, then rise again with progressive structural diversification.
Curve 2: size diversity, vertical complexity, average size, hollow trees, leaf litter depth, bark area per tree, and live biomass rise through succession.
These curves illustrate that different habitat elements respond on different time scales and emphasize that restoration or management targets should consider multiple trajectories.
Successional Pathways and Variability
Succession is not strictly deterministic; multiple pathways can occur after disturbances depending on severity, frequency, and seed/propagule availability:
Theoretical states (e.g., eastern hemlock–American beech) may lead to different outcomes depending on disturbance history and seed sources. For example:
After an intense hurricane followed by a fire that leaves bare soil, paper birch and black birch may dominate initially.
If hemlock seed is unavailable, a beech–birch stand may dominate; if hemlock seed is available, a beech–hemlock stand may develop.
These successional pathways produce several relatively long-lasting forest states, each with a different suite of habitat elements.
Figure 7.9 (Spies 1997) conceptually depicts how stand states can shift with disturbances of varying frequencies and intensities from a disturbance-intolerant to tolerant spectrum.
Succession is therefore a continuum with multiple potential outcomes rather than a single fixed path.
Management Implications: Aligning Disturbance with Goals
Management does not replace natural disturbances but can be complementary.
Knowledge of natural disturbance frequency, severity, and size, plus the potential successional pathways, informs strategies to achieve a variety of goals (Long 2009).
Departures from natural disturbance regimes can push landscapes into states that differ from those in which species evolved and persisted (Cyr et al. 2009).
Disturbances influence forest structure and composition along with other physical factors; management actions must consider climate change and disturbances (Figure 7.11).
A useful approach is to embrace variability in forest structure and composition to meet biodiversity targets while maintaining timber and other ecosystem services.
Silvicultural systems should imitate natural disturbances to varying degrees depending on objectives; intensive timber management often results in less dead wood and fewer noncommercial species, potentially reducing habitat suitability for some wildlife relative to natural disturbances (Hansen et al. 1991).
The challenge is to balance commodity production with habitat and biodiversity goals, using multiple silvicultural systems and management strategies across the landscape to maintain habitat diversity.
In later chapters, methods for stand and forest management that aim to achieve both timber and habitat objectives will be discussed.
Synthesis: What Determines Habitat Elements after Disturbance
The available literature highlights that disturbance severity, size, and frequency interact to shape key habitat elements such as:
Vertical complexity
Forage availability (including mast and soft mast)
Dead wood abundance and distribution
Horizontal complexity and edge effects
Plant species composition and community diversity
Following disturbance, vegetation regrowth follows stand development stages, but the exact trajectory depends on:
Seed and sprout availability
Shade and moisture tolerance of species
Time and climate, soil conditions, and nutrient availability
The same site can realize several different long-term forest states depending on disturbance history and ecological legacies, each offering a distinct habitat element configuration.
Key Numerical References and Formulas (Selected)
Disturbance statistics (annual area affected):
450{,}000\ \mathrm{ha}1{,}000{,}000\ \mathrm{ha}2.0\times 10^{7}\ \mathrm{ha}2.0\times 10^{5}\ \mathrm{ha}0.1\ \mathrm{ha}2\text{–}5\ \mathrm{years}3\times 10^{2}\text{–}4\times 10^{2}\ \mathrm{years}BA = \sum{i=1}^N \pi \left(\frac{di}{2}\right)^2$$ where $d_i$ is the diameter at breast height of tree $i$; BA is measured per hectare
Disturbance frequency ranges and annual area disturbed provide context for planning silvicultural regimes and their effects on habitat elements
In some hardwood forests, 90%–99% of stems may die during early stand development stages, influencing the pattern of dead wood production and habitat resources
Figures and Concepts Referenced (Context Only)
Figure 7.1: Fire-size distribution histogram for 2898 lightning fires (1980–1993) on a logarithmic scale; shows more small fires than large ones.
Figure 7.2: Bison, elk, and other herbivores benefited from large, severe fires in Yellowstone.
Figure 7.3: Legacy trees, snags, and logs retained after timber harvest in Willamette National Forest, illustrating biological legacies.
Figure 7.4: Zones of hurricane frequency in New England with recurrence intervals (Boose et al. 2001).
Figure 7.5: Conceptual stand-development timeline showing stand initiation, stem exclusion, understory reinitiation, and old growth.
Figure 7.6: Crown class differentiation during stand development in an even-aged stand.
Figure 7.7: Repeated low-severity fires can increase forest gapiness and forage availability for species such as white-tailed deer.
Figure 7.8: Generalized patterns of habitat element change over time in Douglas-fir forests (Spies 1998): Curve 1 (U-shaped) vs Curve 2 (sigmoidal).
Figure 7.9: Theoretical changes in forest states during succession and disturbances of varying frequencies and intensities (Spies 1997).
Figure 7.10: Successional pathways for a southern New England forest showing alternative states depending on disturbance and seed sources.
Figure 7.11: Interactions among forest disturbance, climate change, and management.
Figure 7.12: Hypothetical range of habitat-element conditions during stand development and silvicultural management (McComb 2001).
Takeaway Messages
Disturbance characteristics (type, size, pattern, frequency, severity) directly shape habitat elements and succession trajectories.
Biological legacies (dead wood, seeds, fungi, and remnant trees) provide critical habitat for later stages and influence forest resilience.
Stand development follows recognizable stages, but the exact path is variable and influenced by disturbance history, seed availability, and site conditions.
Management can align with natural disturbance patterns to support biodiversity and ecosystem services, but it must balance timber production with habitat goals and accept some inherent variability in outcomes.
Climate change and altered disturbance regimes add uncertainty, underscoring the value of diverse silvicultural approaches that mimic natural disturbance dynamics across the landscape.
Dickinson CH2
Early History of Southern Forests
Ancient Origins: Primeval forests were complex systems of club moss trees and ferns, evolving over time into gymnosperms (like pines) and later mixed gymnosperm and angiosperm (deciduous) forests.
Climatic Shifts: About 20,000 years ago, the northern boreal coniferous forest extended deep into the South due to climatic shifts.
Early Human Impact (Pre-1500 AD):
First humans immigrated to North America around 10,000 B.C., finding beech-maple hardwood forests.
By 5,000 B.C., the climate became warmer and drier, leading to the dominance of oak-hickory and pine-hardwood forests.
Early inhabitants hunted megafauna initially, then switched to deer, turkey, and small game after megafauna extinction.
Woodland people (by 1,000 B.C.) developed simple agriculture (e.g., squash) and influenced landscapes by creating forest openings.
By A.D. 1500, the Mississippian culture used fire as a common tool to influence forests, but this culture later declined.
Influence of Native Americans (Mid-1500s)
Widespread Cultures: Developed Native American cultures were extensive across the southern region, with population estimates up to 1.5 million.
Subsistence: Relied on hunting, growing crops (corn, beans, squash, gourds), and gathering.
Landscape Impact:
Settlements were often on better soils, but they affected drier uplands too.
Used fire regularly and without control to:
Create openings for crops.
Open up the woods.
Drive game for harvest.
Frequent, intense burning on coastal plains favored pines, especially longleaf pine, creating extensive savannahs and grassland prairies in combination with soil conditions.
Fires were less frequent in upland mountainous areas (hardwoods dominated) and usually absent in moist bays, floodplains, and swamps (old-growth hardwoods developed).
Native groups moved periodically, and their influence, along with natural phenomena, created a wide variety of tree and forest age classes interspersed with openings.
They also created openings by girdling trees to clear land for crops.
Pre-colonial Old-Growth Forests (1700s)
Decimated Native Populations: By the 1700s, Native American populations were greatly diminished due to European diseases, reducing their forest influence.
Dominant Landscape: Old-growth forests with structural diversity, large old trees, standing snags, and down decaying logs dominated the South.
Varied Landscape: Pre-colonial old-growth forests comprised a diverse landscape with stands of varying tree ages interspersed with openings. Examples include expansive savannahs, groves, dense cane thickets, swamps, and open pine forests.
Tree Characteristics: Many big, old, decayed trees, standing snags, down logs, and abundant mast.
Regional Forest Types:
Blue Ridge, Ridge and Valley, Appalachian Plateau, Piedmont: Mixed forests, mostly oaks and other hardwoods, with some pines on drier sites. American Chestnut was common in mountainous areas.
Coastal Plain: Comprised of pine and hardwoods.
Fire-resistant pines (especially longleaf pine) dominated upland sites with frequent fire, forming dense stands or pine savannahs with grassy understories.
Hardwoods (especially oaks) were common on clayey soils.
Shade-tolerant magnolia and beech dominated moist sites naturally excluded from fire.
Live oaks on higher ridges along the coast.
Some areas had natural prairies due to soil conditions.
Bottoms: Occupied by oak-gum-cypress forests. One-third of the Lower Coastal Plain of Georgia was gum-cypress or cane swamp.
Understory: Palmetto and cane were dominant, sometimes forming extremely dense thickets.
Dynamic Nature: Southern old-growth forests were dynamic, constantly changing due to natural phenomena and Native American influence.
Natural Plant Succession: Shade-tolerant plants replaced pioneer species.
Major Disturbances:
Flooding and sedimentation in river bottoms.
Insects, diseases, ice and wind storms.
Fire played a major role; though lightning fires were less frequent, Native American fires were a much greater impact, burning annually to create openings and drive game. Repeated burning reduced hardwoods on uplands, favoring pines.
Wildlife Communities (Pre-colonial 1700s)
Habitat Dependent: Wildlife communities were shaped by habitat, natural factors, and Native American influence.
White-tailed Deer:
Widespread and abundant throughout North America.
Extensively used by Native Americans and early settlers for food, clothing, and trade.
Calculated pre-colonial natives consumed 4.6 to 6.4 million deer annually.
Deer hides were the major trade item and main export from southern ports in the early to mid-1700s.
Excellent habitat was a combination of mature forests and openings/savannahs with browse and forbs, created by fire or other disturbance.
Wild Turkey:
Very abundant in diverse pre-colonial forests.
Harvested with ease by Native Americans for food and adornments.
Thrived in diverse forests with hard mast (fall/winter habitat) and openings with grass-forb vegetation and insects (spring/summer habitat).
Squirrels:
Abundant; fox and gray squirrels, and flying squirrels were common.
Gray squirrels thrived in mature, mast-producing old-growth forests.
Fox squirrels preferred more open habitats like pine-hardwoods, pine savannahs, or agricultural areas.
Ducks:
Wood ducks and mallards wintered by the millions in extensive flooded bottoms with abundant acorns and invertebrates.
Wood ducks were common nesters in abundant cavities of old-growth forests.
Other waterfowl (hooded mergansers, green-winged teal, gadwall, American widgeon) frequented flooded bottoms.
Carnivores:
Generally abundant where sufficient diversity and early successional vegetation supported prey.
Bears, cougars ("tygers"), wolves (red wolf), and bobcats were recorded as numerous.
Cougars were widespread and likely supported by abundant white-tailed deer.
Bobcats were abundant where low vegetation supported small mammal densities.
Red wolf was widespread in Coastal Plain and along the Mississippi River delta.
Black bears were abundant due to a combination of mature forests (dens, mast) and openings (small vertebrates/invertebrates, soft mast). They frequented dense cane thickets when hunted.
Birds:
Red-cockaded woodpecker: Probably widespread in fire-maintained old-growth pine forests with old trees for cavities.
Diverse Bird Communities: Old, diverse forests with multiple foliage layers supported greater bird abundance and diversity.
Waders and Avian Predators: Common in flooded forests (e.g., wood stork, Mississippi kite, bald eagle, osprey, red-shouldered hawks, barred owls).
Vireos and Warblers: Abundant in mature mesic and moist riparian forests.
Swainson's and Bachman's warblers: Likely regular occupants of dense cane thickets.
Carolina Parakeets: Abundant, fed on cypress seeds.
Passenger Pigeons: Nesting colonies covered miles, wintered by the millions in southern bottoms, feeding on oak mast.
Cavity-nesting birds: Abundant due to numerous partially-decayed trees and snags in old-growth forests (e.g., red-headed woodpeckers, American kestrels, great crested flycatchers, wood ducks, prothonotary warblers).
Ivory-billed woodpecker: Thrived in southern oak-gum forests, foraging on dead trees.
Settlement and Exploitation (European)
Initial Impact: Early European settlers had little effect on forests except near coastal settlements.
Population Growth & Resource Demands: During the 1800s, America's population surged, increasing demands for natural resources. Pioneers moved into the Southeast.
Conflict with Native Americans: Hostilities led to the eviction of most natives (e.g., "Trail of Tears").
Settlers' Mindset: Regarded mature southern forests as "wilderness to be conquered"; natural resources were considered inexhaustible and exploited.
Forest Use by Settlers:
Cleared openings for crops (corn) and livestock pasture.
Wood used extensively as fuel (over 90% of nation's heat energy by mid-1800s), for building houses and barns, and for shipbuilding.
Turpentine and naval stores were major products from longleaf-slash pine areas.
Commercial Logging Boom:
Initially piecemeal, but by mid-1800s, demand had substantial effect.
Railroads facilitated timber transport; wood used for crossties.
Lumber industry shifted from north to the South in the late 1800s as northern forests were exhausted.
Nation's total lumber production and southern pines peaked in 1909.
Vast longleaf pine forests (74 million acres) were virtually all felled from about 1870 to 1920 due to extensive commercial logging and new steam technology.
Hardwoods and cypress were also heavily harvested for various products.
Bottomland Forest Conversion:
Drastic loss of bottomland hardwoods, especially in the Mississippi River Delta.
From 11.8 million acres in the 1930s to 7.2 million acres by the early 1970s.
Converted mainly to soybeans, improved pasture, and cotton.
Other causes: man-made lakes and logging.
Overall Impact on Forests: Devastated by unrestricted logging in the late 1800s and early 1900s, with little thought for regeneration, leading to depleted soils.
Wildlife Demise (Exploitation Era)
Attitude: Settlers regarded large carnivores as threats or competitors; wild animals were harvested easily for food and commerce.
White-tailed Deer:
High demand for hides and food.
Populations plummeted to less than a million by 1900 due to intense market demand, wide-spread harvest facilitated by repeating rifles, and railroad access.
Wild Turkey:
Demise due to expansive settlement, unrestricted harvest, market hunting, and widespread habitat degradation from wholesale logging.
Disappeared from 18 states by 1920, reduced to 28% of original range by 1940s.
Wood Duck: Drastic reductions by early 20th century, likely due to overharvest at roost sites.
Black Bears: Decimated as they were seen as predators of livestock/crops, hunted for food/lard, and distribution reduced to 5-10% of former range.
Passenger Pigeon:
Once numbered over a billion, wintering in southern bottoms.
Demise due to clearing of hardwood bottoms and ease of market killing, possibly exacerbated by social reproductive behavior. Last one died in 1914.
Carolina Parakeet: Attracted to settlers' crops/gardens, making them vulnerable to guns.
Ivory-billed Woodpecker: Last confirmed specimen taken in 1943 when its mature bottomland forest habitat was cleared for soybeans.
Bachman's Warbler: Extinct or nearly so, probably due to extensive clearing of Mississippi River and West Gulf Coastal Plains bottoms.
Other Species: Many shore birds and large forest birds harvested for food and plumes (for hats). Clearing of bottoms eliminated nesting areas.
Overall Impact: Southern forests and their wildlife were substantially impacted by the rapidly growing settler population and their demands, with little provision for long-term natural resource management.
Dickinson CH4
Defining the Forests
Diversity and Productivity: Southern forests are very diverse and productive, ranging from boreal spruce-fir forests on high Blue Ridge mountain peaks to bottomland hardwoods near sea level. They also include upland hardwood stands in northern mountainous areas and southern pines/hardwoods along the Coastal Plain.
Climate:
Predominantly continental, except for the cooler Appalachian Mountains, grading to maritime along the coast.
Temperatures: Generally mild in winter and hot in summer.
January mean maximum: 40s (mountains) to 70s (Florida).
January mean minimum: 20s (mountains) to 60s (Florida).
July mean minimum: mid-50s (mountains) to 70s (Gulf Coast/Florida).
July mean maximum: ~90 for most of the region, slightly lower in mountains.
Freeze-free period: Varies from 150 days (higher eastern mountains) to 300 days (Gulf/lower Atlantic coasts) or longer (peninsular Florida).
Precipitation: Well-watered, most areas receive >38 inches annually, all receive >40 inches. Occasional mountain peaks and Mississippi River mouth coastal areas receive >60 inches. Driest parts (40-45 inches) are east of Appalachians (parts of Virginia, central SC/GA) and western Oklahoma/Texas.
Soils: Primarily formed by climate, parent material, organisms, topography, and time. Shaped by a warm, moist environment, except for cooler high mountains and drier western edge. This climate, combined with geologic stability, produced soils with considerable pedogenic alteration.
Physiographic Regions (Key Characteristics & Forests)
Lower Coastal Plain:
Broad flats and nearly level uplands, about 54% forested.
Almost level flatwoods dissected by rivers and swamps.
Elevations <90 ft; poor soil drainage.
Soils: Mostly sand, silt, clay; dominant Ultisols (except beach Entisols).
~90% forested. Historically, mature longleaf pine forests, now often loblolly and slash pine plantations due to cutting and diminished fire.
Upper Coastal Plain:
Broad uplands and low plateaus, geologically older than Lower Coastal Plain.
Greater dissection, topographical relief, soil development.
Elevations 90-600 ft; dominant Ultisols.
Forest cover varies: 25% (peninsular Florida) to 70% (west of Mississippi River in LA/TX).
Dominant pine and pine-hardwood forests, loblolly pine common.
Piedmont:
Second largest physiographic area, stretching from Georgia to Virginia.
Rolling upland plain from diverse metamorphic/igneous rock.
Moderate elevation (300-700 ft).
Soils: Ultisols (acidic rocks), Alfisols (basic igneous rocks), Inceptisols (steep slopes).
About half forested. Dominant pine and pine-hardwood forests, loblolly pine common.
Mississippi River Valley:
Splits the South, mostly nearly level river valley.
Low elevations (sea level to 520 ft).
Soils: Variable mixture of alluvial deposits.
Dominant soil orders: Entisols (active floodplain), Inceptisols (low alluvial terraces), Alfisols and Mollisols (mid-elevation terraces), Alfisols (older, higher terraces).
Only 27% forested. Historically oak-gum-cypress forests predominated.
Loess-covered uplands east of Mississippi: Thick wind-blown silt up to 60 ft deep. Dominant Alfisols interspersed with Ultisols. About half forested, characteristic red oaks, white oak, yellow poplar.
Blue Ridge Mountains:
Highest mountains in the South, Virginia into Georgia.
Elevations 1,000-4,000 ft, peaks almost 7,000 ft; steep slopes.
Subsurface: Predominantly igneous and metamorphic rocks.
Soils: Inceptisols (steep slopes), Inceptisols and Ultisols (lesser slopes).
94% forested.
Ridge and Valley:
Narrow belt west and parallel to Blue Ridge, Virginia into northern Alabama.
Limestone/shale valleys (~600 ft elevation) bounded by steep-sided ridges of sedimentary rock.
Soils: Primarily Ultisols (limestone), some Alfisols; Inceptisols (sideslopes/steep ridges).
About 3/4 forested.
Appalachian Plateaus:
West of Ridge and Valley, eastern Kentucky, substantial Tennessee.
Deeply dissected plateaus with rolling topography.
Elevations 1,000-2,000 ft (some exceed).
Substrate: Sandstone (plateau), eroded shale (sideslopes).
Soils: Dominantly Ultisols (flat uplands, valley floors, escarpments, valley slopes).
72% forested.
Note on Mountainous Areas (Blue Ridge, Ridge & Valley, Appalachian Plateaus): Dominated by various white/red oaks with hickories and yellow poplar.
Interior Low Plateau:
West of Appalachian Plateaus, middle Kentucky/Tennessee, into Alabama.
Extensively dissected rim with moderate elevations (300-900 ft).
Underlain by limestone.
Soils: Alfisols (plateau interior), Ultisols and Alfisols (dissected rim).
Two-thirds comprised of upland oak-hickory forests.
Arkansas Valley and Ridges:
North of Ouachita Mountains; broad river valleys and ridges.
Elevations and soils similar to Ouachita Mountains, except Alfisols over shallow limestone.
Slightly over half (52%) forested.
Ozark Plateau:
North; deeply dissected plateau, narrow ridgetops with steep sideslopes.
Considerable relief, moderate elevations (500-1,500 ft).
Soils: Ultisols (ridges/uplands), Inceptisols (sideslopes), Alfisols (valley floors over limestone, dolomite, shales).
Upland forests dominate (80%). Similar to Ouachita forests but pines scarcer, hardwoods more dominant.
Central Lowlands:
West of Ouachita Uplands; broad flats and rolling hills.
Low elevations (400-1,300 ft).
Soils: Sandstones, shales, clays; dominant Mollisols interspersed with Alfisols (alluvial areas).
Only 8% wooded. Characteristic oak-hickory forests (post and blackjack oaks).
Forest Influences (Dynamic Nature)
General: Southern forests are dynamic and diverse, continually changing due to natural factors and human use.
Wind Storms: Major role in shaping forests.
Example: Hurricane Hugo (1989) struck coastal South Carolina (Charleston) with >150 mi/h winds, drastic impact on people and forest. Killed 35, $6 billion property damage, >4 million acres timberland damaged/destroyed, nearly 11 billion board feet sawtimber. Pine overstory eliminated, replaced by brushy hardwood understory.
Ice Storms: Affect southern forests. Conifers (long persistent needles) are vulnerable. Slash pine, extensively planted, is vulnerable to breakage and may not reach rotation age.
Diseases:
American Chestnut Blight: Introduced, spread rapidly, eliminated American Chestnut from eastern forests in early 1900s. Roots resprout but succumb to blight.
Dogwood Anthracnose: Fungus, introduced with Asiatic dogwood in NE U.S., moved south into Southern Appalachians. Affects plants above 3,000 ft.
Southern Pines (main widespread diseases):
Fusiform rust: Affects loblolly and slash pine seedlings/saplings; annual economic losses >$100 million. Oaks are alternate hosts.
Littleleaf syndrome: Most serious disease for shortleaf pine, higher incidence on poorer sites.
Annosus root rot: Major disease, reduces growth, causes mortality. Stumps/roots from harvest operations provide entry.
Many other fungi infect southern hardwoods.
Insects:
Southern Pine Beetle: Important economic pest of southern pines. Affects millions of acres during outbreaks. Pines under stress/low vigor are vulnerable, but epidemics affect wide variety of pines. In mixed stands, killed pines are replaced by shade-tolerant hardwoods.
Balsam Wooly Adelgid: Threatens Frasier fir (only in high elevations, Blue Ridge Mountains). Feeds on main tree bole, kills trees. Introduced to New England in early 1900s, spread south.
Gypsy Moth: Substantially affecting southern upland hardwood forests. In eastern mountains, defoliates mostly oaks, reduces vigor; repeated defoliations can cause mortality.
Man's Direct Influences:
Harvesting: Virtually all Southern forests molded by man. Often selective for certain species, leaving lesser value/poorer form trees.
Bald cypress (bottoms) and Longleaf pine (Lower Coastal Plain) have diminished most. Cypress was prized for decay resistance and easy working. Longleaf pine for light weight, large size, cylindrical shape, clear lower limbs.
These species were rarely regenerated back to same species after cutting due to slow growth. Longleaf pine acreage: 90 million acres reduced to <3 million today.
Alteration of Flooding: Creation of reservoirs, channelization, other land/water manipulations affect site characteristics and tree composition.
Example: Atchafalaya Basin, LA, built for Mississippi River floodwaters, became higher and drier due to siltation; swamp forests replaced by cottonwood/willow stands and soybean fields.
Pollutants: Ozone can injure trees. Main air pollutant in the South due to sunny days, high automobile/industry emissions of hydrocarbons/nitrogen oxides (ozone precursors).
Status of the Forests
Acreage: Forests dominate southern landscape, covering ~214 million acres (a little over half).
Commercial timberland: 94% of total.
Most heavily forested states (over 15 million acres and >60% forested): Georgia, Alabama, Mississippi, North Carolina, Virginia.
Least forested areas: Southern Florida, Mississippi River Delta, western edge of region, urban/agricultural areas.
Composition:
Over half (52%) timberland is hardwoods.
Upland hardwood forests: 75 million acres (~37% of timberland), increased recently. >Half of timberland in KY, TN, VA, OK. Oak-hickory association throughout most of region, predominates in mountainous areas (Southern Appalachians, Ouachita Uplands). Common species: oaks, hickories, yellow poplar, sweetgum, American beech, red maple.
Bottomland hardwood forests: ~15% of timberland (~30 million acres). Over half in alluvial floodplain of major rivers (LA, FL, GA, MS). Prevalent species: water, willow, laurel, swamp chestnut, cherrybark oaks; tupelo, blackgum, sweetgum, baldcypress.
Mixed oak-pine stands: >half hardwoods, 25-50% pines. ~29 million acres (14% of timberland). Occur throughout region.
Pine types: Approximately 1/3 of southern timberland.
Natural pines: ~36 million acres (18%), declined recently. Loblolly pine most common. Prevalent in Coastal Plain and Piedmont, pioneer abandoned land. Shortleaf pine dominant at higher elevations (Southern Appalachian Plateau, Ridge and Valley, Ouachita Uplands).
Pine plantations: ~31 million acres (15%), increased significantly. Comprise 1/3 of Florida timberland, >1/4 in lower Coastal Plain (SC, GA, AL, MS, LA, eastern TX). Loblolly most widely planted, slash pine in southerly areas. Some effort to reestablish longleaf pine.
Age: In last 2 decades, southern forests have aged. Sapling and pole-sized trees less abundant, sawtimber-sized trees increased. Sawtimber more abundant in pine/pine-hardwood stands and dominant in upland/bottomland hardwood stands.
Ownership:
Dominantly private: ~2/3 of southern timberland (138 million acres) owned by nonindustrial private forest owners.
Forest industry: ~20% (41 million acres). Higher in the "deep South" where more valuable pines dominate (LA, eastern TX, FL, GA, AL, AR: >25% industry control).
Public land: ~10% (21 million acres) in National Forests (11 million acres) and other federal, state, municipal land. Over half of National Forest timberland in AR, VA, MS, NC. Upland hardwoods predominate on National Forests in Appalachians; natural pine, upland hardwoods, mixed pine-hardwoods elsewhere.
Nonindustrial private land dominates northern portion where upland hardwoods are common (>3/4 in KY, TN, VA, NC).
Economic Value
Timber is a very important economic commodity.
Harvest (1984): 7.5 billion cubic feet roundwood products harvested.
Softwoods (primarily southern pine): >5 billion cubic feet.
Hardwoods: ~2.5 billion cubic feet.
Value (1984):
Stumpage value: $2.7 billion (softwoods), $0.4 billion (hardwoods).
Value added (harvesting & transportation): $6.1 billion ($4.5 billion softwoods, $1.6 billion hardwoods).
$6.1 billion product value was ~twice soybeans/cotton, ~three times tobacco.
Economic Impact: Forest industries contributed ~10% of value added to southern economy and employed ~10% of southern workers.
Agricultural Crop Ranking: Timber ranked among top three agricultural crops in value in all southern states, and first in value in 6 states: Virginia, South Carolina, Georgia, Alabama, Mississippi, Louisiana.
Increased Harvest: Value increased recently due to increased wood demand and harvest restrictions in Northwest. In 1991, South accounted for 55% of domestic growing stock removals (up from 45% in 1970).
Wood Products
Pulpwood: Smaller or lower-grade trees for paper/reconstituted wood products.
1996: 2.4 billion cubic feet softwood, 1.5 billion cubic feet hardwood. 41% of total roundwood production.
Sawlogs: Larger trees cut into lumber.
1996: 2.7 billion cubic feet softwoods, 959 million cubic feet hardwoods. 38% of roundwood harvest.
Veneer logs: Relatively large, high-quality logs for furniture, cabinets, plywood.
~9% of roundwood volume, but higher proportional stumpage value. ~5 times more softwood than hardwood volume.
Fuelwood: ~10% of roundwood production for industrial/residential use. Primarily hardwoods (24% of hardwood harvest), only ~3% of softwood harvest.
Other Products: Collectively ~2.5% of roundwood production; not regionally important but locally significant. Includes poles, pilings (softwood), fenceposts, cooperage logs, mine timbers, shingle bolts, handle bolts, wood turnings, panel products, chemical wood.
Silviculture
Purpose: Employed to harvest and regenerate southern forests.
Even-aged Systems: Used when intolerant to mid-tolerant species are favored.
Clearcutting: All stems removed. Natural regeneration often adequate in small clearcuts (several acres); planting necessary in larger clearcuts without advance regeneration of desired intolerant species.
Seed tree cut: 8-12 mature trees per acre left to seed and regenerate stand. Uses natural regeneration.
Shelterwood cut: Overstory trees removed in 2-3 partial cuts, moderating harvesting effects over time. Uses natural regeneration.
Intolerant southern pines usually maintained in even-aged stands because they are replaced by more tolerant hardwoods without full light.
Uneven-aged Systems: Maintain at least 3 tree age classes.
Single-tree selection.
Group selection.
Hardwoods can be maintained in even-aged or uneven-aged stands. Upland and bottomland hardwoods are regenerated satisfactorily with group selection or small clearcuts (at least 2-3 acres) that allow full sunlight and where advance regeneration is present.
Site Preparation: Conducted to expose seed bed, eliminate logging residue, or reduce competing vegetation.
Usually not necessary for hardwood stands with advance regeneration.
Sometimes used in regenerating pine stands.
Methods: Burning, mechanical means, herbicides.
Thinning: Intermediate treatment in longer rotation stands to harvest part of stand and redistribute growth.
Normally applied in 10-15 year-old and older pine stands grown on a sawtimber rotation.
Pine stands often burned when thinned.
Rotations (Age at Harvest): Variable, depending on products/objectives.
Some forests managed as old growth/wilderness (not harvested).
Most managed for sawtimber and/or pulpwood production.
Sawtimber rotation: Trees grown for sawtimber should be large and free from lower lateral limbs. Typical is 60-100 years for southern pines and faster-growing bottomland hardwoods on well-drained sites; somewhat longer for upland hardwoods.
Pulpwood rotations: Typically 20-30 years for fast-growing pines; somewhat longer for slower-growing hardwoods.