The data of Wilbur and Christensen [87], suggest that pocosin peats are deficient in nutrients, particularly phosphorus. Burning resulted in considerable enrichment of most available nutrients, and some amelioration of the prefire phosphorus deficiency. They believe these nutrient changes are responsible in part for increased postfire production. However, increased fertility following fire was short-lived, and by the 2nd growing season concentrations of most nutrients were back to prefire levels.
Not only were mean concentrations of particular nutrients elevated following fire, but spatial variation in those concentrations was also increased. This was particularly true for nitrogen and phosphorus. Thus, high and low nutrient patches were created in an area characterized by uniformly low prefire nutrient concentrations. This redistribution of resources might lead to the creation of patches of high and low production within a bog [87].
Mature trees sprout vigorously from protected buds along the bole, main branches, and root
crowns [10,13,32,39,60], and are only killed by severe fires [6,13]. Repeated fire would favor pond pine over loblolly pine because of pond pine's ability to sprout vigorously [42]. However, one study suggests that the ability to sprout is generally restricted to seedling and saplings [45]. After a fire burned through a pine scrub on Cumberland Island in Georgia, tree mortality was very high (95-100%) in plots where pond pine was a strong dominant. Pond pine seedlings found in the first 2
postfire seasonal samples did not survive [18].
Heat generated by a ground fire is usually of
sufficient intensity to open the serotinous cones of pond pine [6]. Pond pine cones do not
characteristically remain closed for longer than 4 to 5 years [79], and observations suggest that
cones open rapidly on felled trees during
midday on clear summer days [6,83] when the outside temperature may be sufficient to open the cones. Seeds up to 14 years old have been germinated [83]. Pond pine cones germinate best after a burn on soil that is moist. This may be because the root system of pond pine is superficial and the seedlings many not be able to obtain enough water to survive in dry conditions [6].
Fire removes competition, exposes the soil and causes the seed of
pond pine to fall. Volume of seed caught in traps averaged about 3,000 sound seed per acre per year for undisturbed and unburned seed tree stands.
From 2 uncut but burned stands
the average was 53,000 sound seed/acre over a 6-week period following the burn
[16]. After a fire on Cumberland Island, Georgia, pond pine, loblolly pine, and slash pine reseeded where the pine canopy was killed
[9].
Season of burning is largely determined by availability of ignition sources and seasonal variation in fuel flammability. A major factor affecting flammability is seasonal variation in moisture. Seasonal variation in the dead-to-live
ratio is also important in shrub bogs [14]. Low-severity winter fires are valuable in preparing favorable seedbeds for establishment of pine seedlings and in partially controlling
associated hardwoods [43]. Most wildfires in the pocosins occur during the early spring and before the evergreen vegetation has increased its moisture content through spring growth
[44].
Pond pine has adaptations that not only allow it to exist, but to thrive in frequent FIRE REGIMES [34,76]. Requirements for fire adapted species such as pond pine are (1) bare mineral or exposed substrate for seed germination, (2) removal of toxic or allelopathic chemicals or disease-causing conditions, (3) reproductive structures requiring fire to disperse propagules, and (4) ability to vegetatively reproduce by root suckering, stump sprouts or epicormic stems [54]. Pond pine readily sprouts after fire, both from root collar and stem, and is one of the conifers most able to endure fire defoliation [10,32,70] because it also produces epicormic branches [60]. Other characteristics of pond pine that contribute to its fire resistance include: medium-thick basal bark; moderate-to-high and open crown; moderately open stands; and medium rooting habit [10,19].
FIRE REGIMES:
Many southeastern habitats have FIRE REGIMES with frequent fire. Fires recurring at intervals of 20 to 40 years have long been recognized as an integral part of the ecology of pocosins dominated by pond pine [87]. The high incidence of fires in longleaf pine communities, which often contain pond pine, is related to their high flammability, a consequence of the volatile oils and resins in longleaf pine needles and wiregrass that is common in the understory. However, human fire suppression has reduced the high natural occurrence of fire in this habitat. Noss [55] stated that an immediate priority for longleaf sites is to reestablish the natural regime of summer fires. Wet pine forests, which include pond pine, depend on fire for their continued existence [25]. Pond pine can be found in wet savannahs in North Carolina that are dependent on fire to eliminate encroaching forests and to remove grass and sedge foliage that casts a heavy shade and can lead to a loss of smaller grasses and forbs which grow between pine clumps [80].
Pond pine communities are wet and nutrient-poor and are most susceptible to fires during droughts that allow the organic soils to dry. The large amount of fuel produced by the understory makes fires severe. However, all dominant species sprout readily and the shrub layer grows to its former height in just a few years. In the wetter, shrub-dominated slash pine and pond pine wetlands, presettlement fire frequency was probably 10 to 30 years. Frequency in these types depends on occurrence of drought conditions sufficient to increase the flammability of the understory to where it will burn readily. Such fires are intense and usually burn all aboveground vegetation, especially in pond pine woodlands [25]. Burning may be severe in both swamps and marshes during prolonged periods of low rainfall. In fresh-water marshes, in which pond pine occurs, fires cause little damage when surface water is present, but may destroy all the marsh dominants as well as the component animal life, such as beaver and muskrat, during drought years when the water table is well below the marsh surface [57].
The following table is a summary of the fire frequency of nonalluvial wetland communities of the southeastern United States in which pond pine is a canopy dominant [72].To learn more about FIRE REGIMES and fire ecology of communities where pond pine occurs with other dominants, refer to the FEIS Species Review of the dominant species listed below. Find further fire regime information for the plant communities in which this species may occur by entering the species name in the FEIS home page under "Find FIRE REGIMES".
Community or Ecosystem Dominant Species Fire Return Interval Range (years) Atlantic white-cedar Chamaecyparis thyoides 35 to > 200 slash pine Pinus elliottii 3-8 slash pine-hardwood P. e.-variable longleaf-slash pine P. palustris-P. e. 1-4 [11] pitch pine P. rigida 6-25 [12] loblolly pine P. taeda 3-8 cabbage palmetto-slash pine Sabal palmetto-P. e. baldcypress Taxodium distichum var. distichum 100 to > 300 pondcypress T. d. var. nutans 11]Pond pine is found on a variety of sites in the southeastern United States. Pond pine occupies the wettest sites within the wet pine type. It is found in swamps, pond borders, and pocosins, characterized by undrained peat soils and/or wet, sandy flats. Pond pine grows extensively in the broad, poorly drained interstream areas of peaty soils in the lower coastal plains of North Carolina. Further south, it is found on wet pine flatwoods (pine forests on poorly drained soils) and savannas of the lower coastal marine terraces and in bays and ponds throughout the coastal plain [25].
In eastern North Carolina, pond pine usually occurs on wet flats and extensive, poorly drained evergreen shrub bogs called pocosins. These pocosins have organic soils varying from 1 to 25 feet (0.3-7.6 m) deep [16,61]. Pocosins are highmoor, ombrotrophic bogs dominated by a continuous shrub cover 3.3 to 13 feet (1-4 m) high with scattered emergent trees, usually pond pine [61,87]. Pond pine is the only "important" pocosin tree, probably because of recurrent fire. Pocosins apparently represent the lower limit of site quality tolerated by pond pine [66].
A pond pine-slash pine association occurs in peaty swamps. Peaty swamps contain surface water only during a part of the growing season. Coniferous trees or shrubs, including many ericaceous species, exist in these swamps. Frutescent and herbaceous plants are also numerous. Peaty swamps are found on poorly drained, flat, interstream areas of lower terraces in the Atlantic and Gulf coastal plains [57].
Pine flatwoods is one of the most common vegetation types in Florida, and can be dominated by pond pine [50]. Flatwoods with a pH less than 4.5 are usually dominated by pond pine and those with pH above 4.5 by slash pine or longleaf pine [50,51]. Pond pine is a principal tree species characteristic of this wet pine type that is found in the coastal plain physiographic province from Delaware south to Florida and west to eastern Texas, primarily in the flatwoods of the outer marine terraces. Representative sites include boggy, nonriver flatlands; poorly-drained, seasonally-wet coastal flatlands; and lowlands adjacent to ponds, streams, and other wet areas. Soils range widely in texture from clay to sand. Moisture conditions are influenced by an impermeable clay soil layer that resists downward movement of water. Poor drainage limits aeration of the soils on many sites and peat mats commonly develop over mineral surfaces. Acidic conditions prevail on most sites [25].
The bay forest type, occurring exclusively in the Coastal Plain physiographic province ranging from Maryland to southeastern Texas, is restricted to coastal depressions or floodplains where saturated conditions prevail. Soils are usually organic, highly acidic and low in nutrient availability [47]. Bay swamps, dominated by the redbay-sweetbay association, are characterized by a more or less dense growth of evergreen trees, including pond pine [57].
Other sites that include pond pine are cypress-swamp tupelo (Nyssa biflora) and cane (Arundinaria spp.). On a cypress-swamp tupelo site, pond pine is most abundant where standing water or poor drainage renders the habitat more acidic [4]. Pond pine is often the overstory of cane habitats that generally occur on organic soils having fair internal drainage and 40% to 50% organic matter content in the upper 4 inches (10 cm) of soil, and a species composition of 70% to 100% reeds [6,29,85].
Pond pine has excellent growth on better drained mineral soils, but the faster, earlier growth of slash and loblolly pine usually restricts it to a subordinate position on such sites [25]. Pond pine is relatively tolerant to waterlogging. Mature trees can tolerate prolonged flooding, but growth is slow. Pond pine also endures poor soil aeration and high acidity, and is confined mostly to ponds and bays of interstream areas [27,57].
Another site characteristic important to maintenance of pond pine is the unique climate of the southeastern United States. Weather patterns in the Southeast spawn more lightning storms than in any other region of North America. The lightning fire season begins in early spring, is often most prevalent in May or June, then tapers off in July and August through early fall. The large majority of fires in the Southeast are caused by lightning [38].
Bottomland forests, in which pond pine is found, tend to be among the most productive habitats for wildlife, with surface water that moderates temperature extremes and serves as escape habitat. There is a predominance of broad-leaved evergreen plants in the understory and mast-producing trees in the overstory that provide an abundance of branch cavities and mast for over-wintering migrant birds [56]. Animals found in pond pine habitat in North Carolina include the marsh rabbit, silver-haired bat, eastern cottontail, grasshopper mouse, meadow vole, black bear, long-tailed weasel, and bobcat [15].
Pocosins, in which pond pine dominates the overstory, serve as habitat for the specialized swallowtail, Hessel's hairstreak butterfly, the rare pine barrens tree frog, the eastern diamondback rattlesnake (endangered in North Carolina), and the federally endangered American alligator. Pocosins are also refuges for native species such as black bear, white-tailed deer, and smaller mammals such as the bobcat, marsh rabbit, and gray squirrel [61,62]. The endangered red-cockaded woodpecker inhabits mature pond pine in pocosins [17,28,61,62,73].
Pond pine often dominates the flatwoods habitat that supports various populations of birds and small mammals such as the cotton rat, cotton mouse, and short-tailed shrew. Avian densities are low throughout the year with some increase in winter due to the influx of migratory winter residents. No mammal is exclusive to the flatwoods, although the fox squirrel is highly characteristic of flatwoods with open understory. Three large mammals native to Florida use flatwoods: white-tailed deer, black bear, and the endangered Florida panther [2].
Pond pine may not sprout after severe fire. For example, it did not sprout after a severe wildfire on the Air Force Bomb Range in Dare County, North Carolina. See Fire Case Studies for further information.
The specific epithet of pond pine, serotina, means "late" and refers to the delayed opening of cones. Cones often persist for 2 to 8 years, giving the tree the appearance of being a prolific seed producer [8,14]. All pond pine cones are probably closed when they first mature [79]. Viability does not decrease in cones that remain closed for as long as 3 years [8]. Cones older than 5 years may open individually following weathering and insect depredations; sound seed may be sparse in cones more than 5 years old [79]. Seed is released from older, open cones of pond pine during 2 seasonal periods: April through September and October through January [8,16]. Regeneration of pond pine is hampered by 2 problems under average conditions. First, serotinous pond pine cones often require heat to open the scaled cones, and 2nd, continual moistness of the organic soil provides an excellent growth medium for intense competitors such as other trees, evergreen brush, and switchcane (Arundinaria gigantea ssp. tecta) [16].
Pond pine cones open and release seeds soon after exposure to heat from fire. Intensity of heat does not adversely reduce viability of seeds. Even badly charred cones release seeds that are capable of germination. Mature cones can be opened by exposure to 333 to 336 oF (167-169 oC) dry heat for 20 seconds or by immersion in boiling water for a similar period [8]. Optimum stratification of pond pine seeds is 30 days at 33-41oF (0.5-5 oC) in a moist medium [5,46]. Germination occurs in 24 days [5]. Pond pine seeds germinated in a nursery were unable to survive full saturation conditions [46].
Among pine species, pond pine is somewhat unique in that it usually sprouts after being damaged by disturbance [8,19,20,24,82]. Seedlings or saplings usually sprout prolifically when cut, and older trees will sprout vigorously along the stem and branches even after intense scorching and defoliation by fire. These sprouts come from dormant buds in the axils of primary needles of young seedlings. Buds are dormant and are protected by bark. When the tree is injured, these buds resume growth and may give rise to clusters of buds and numerous short shoots [8]. In pocosins, seedlings of pond pine sprout prolifically, and stands up to sapling size are primarily reestablished by sprouting [29]. However, 1 study showed that most seedlings on pond pine plots, which were completely burned, did not sprout [66]. Evidence suggests that pond pine may not sprout indefinitely, and that frequent burning of any age pond pine stand may kill it [26].
The successional status of pond pine is somewhat controversial. Traditional ecological succession and climax concepts tend to place many of the fire-dependent vegetation types, such as pond pine, as "subclimax" types [2,8,15]. However, others believe the fire-dependent systems are relatively stable "climaxes" under a burning regime, if, historically, fire was a natural part of the environment [54,81]. Walker [81] considers pond pine climax vegetation in pocosins since the tree is maintained in the absence of fire and regenerated as a consequence of fire. The bay swamps, many of which contain pond pine, are considered climax by some, since the southern white-cedar swamps revert to redbay-sweetbay when protected from fire; however it is stated that the hydric communities "can not be considered climax because none are controlled by climate [57]."
Fire is an important aspect of succession in many habitat types in which pond pine is found. The long-term perpetuation of flatwoods, sand-pine scrub, pocosins, and savannas are tied to fire. Species diversity is highest immediately following fire and generally decreases thereafter [13].
Flatwoods ecosystems, along with the rest of the southeastern pine forests, have been classified as fire subclimax within the deciduous forest region [2]. Pine flatwoods are considered to be fire maintained but, without fire, they ultimately give way to hardwoods [50]. Pond pine flatwoods, if unburned, can develop either to bayheads or to mixed hardwood swamps [2,8]. Pond pine communities of North Carolina possess little herbaceous vegetation and are often changed by fire into shrub swamps in which pond pine occurs only as scattered relicts among the fire resistant shrubs [57]. Human alteration of natural fire frequency is thought to be the most common cause of successional change in flatwoods [2].
Pocosins, often with pond pine overstory, generally can be viewed as intermediate successional communities. They are often maintained in a subclimax stage by fire and hydroperiod, with the mature vegetational stages being suppressed for long periods on the wettest sites but developing relatively quickly on drier sites [15].
The bay forest type, occurring exclusively in the Coastal Plain physiographic province, frequently reverts to pond pine or Atlantic white-cedar after severe fires [47]. If the original stand of southern white-cedar is destroyed, together with seed stored in the upper layer of peat, succession is toward a type in which pond pine predominates in Virginia, North Carolina and South Carolina [35]. With recurrent fire, the bay swamp, pond pine-slash pine wetlands, and Atlantic white-cedar bog may revert to shrub bogs [47]. It should be noted, however, that the shallow marsh is characterized by a mineral soil, and could not arise in a peaty area without aggradation of inorganic sediments [57]. The patchwork nature of evergreen bay forests is related to their extreme susceptibility to fire, after which they may revert back to any one of several freshwater, hydric vegetative cover types depending on the intensity of the burn and depth to the water table during and following the burn [47].
Frequency of fire also determines the successional stage of many southeastern swamp forests. Serotiny of species such as pond pine may be selected for in regimes where fires are spaced with a frequency which allows maturation but does not "unreasonably exceed" this. Too frequent firing could eliminate pond pine from an area altogether [26] and produce a grass-sedge bog or savannah [8]. Wells [84] observed that fires started by Native Americans, and later even more frequently by European settlers, began to change stream-head swamp forests of the southeastern United States into grass-sedge bogs or savannahs. Under burning at least every decade, the native deciduous forest largely disappeared or became dominated by pond pine. With more frequent burning the pines were replaced by fire-resistant shrubs or shrubby trees with the ability to sprout from stumps or roots. Under annual fires, the shrubs practically disappeared and were replaced by grasses, sedges, and many bulbous herbs. These nearly treeless areas were called sub-tropical savannahs. Under reduced frequency of fires, savannahs revert to shrubby pocosins, and under no fire, savannahs and pocosins rapidly return to swamp forest.
Excluding fire, primary factors affecting plant succession in any hydric area are aggradation of the level of the substratum by inorganic and organic sediments, with consequent lowering of the water table and subsequent increase in oxygen tension above that level [57]. On organic soils subject to prolonged flooding, longleaf and slash pine are replaced by pond pine communities. Pond pine assumes dominance in Virginia and the Carolinas on the wettest sites and on organic soils [25]. On mineral soils, pond pine is in an intermediate stage of plant succession, where it may grow in pure even-aged stands until harvesting or mortality removes the dominant trees [8].
The economic value of pond pine is variable. Some consider pond pine a commercially valuable species [40] as a timber source [36]. However, others have determined pond pine has low economic value as a pulpwood source [20]. The wood is course-grained, resinous, and of fair quality. Pond pine is apt to have more defects than other southern pines on the market, largely due to its susceptibility to red heart disease which substantially reduces its lumber value [8] and may make it more susceptible to fire damage [66]. Pond pine has not been widely cultivated, due to its "low" economic value [59].
Pond pine is the principal commercial species of the pocosins of North Carolina. According to Besse [6], in 1952 the tree occurred on approximately 2 million acres of the coastal plain of North Carolina and the total board foot volume was 1.75 billion board feet. On wet sites characteristic of present day pond pine forests, yields are comparatively low, and logging costs are high. Observations indicate that growth rates of pond pine may be 25% to 33% lower than loblolly pine where the species grow together [66].
