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SPECIES: Pinus palustris


Carey, Jennifer H. 1992. Pinus palustris. In: Fire Effects Information System, [Online]. U.S. Department of Agriculture, Forest Service, Rocky Mountain Research Station, Fire Sciences Laboratory (Producer). Available: [].


Pinus australis Michx.


longleaf pine
longstraw pine
southern yellow pine
longleaf yellow pine
swamp pine

The currently accepted scientific name of longleaf pine is Pinus palustris Mill. [7,31]. There are no recognized varieties or subspecies. Longleaf pine forms natural hybrids with loblolly pine (P. taeda) and slash pine (P. elliottii), although the latter are rare [7,26].


No special status

Only a few old-growth stands of longleaf pine remain in the southeastern United States [43]. Although longleaf pine is not an endangered species, many endangered plant and animal species live in longleaf pine communities. Longleaf pine communities are ranked as threatened by the Texas Natural Heritage Program [9].


SPECIES: Pinus palustris
Longleaf pine occurs in the Atlantic and Gulf coastal plains from southeastern Virginia to central Florida and west to eastern Texas. It is found in the Piedmont Region and Valley-and-Ridge Province of Georgia and Alabama [7,31].

FRES12 Longleaf-slash pine
FRES13 Loblolly-shortleaf pine
FRES14 Oak-pine

STATES/PROVINCES: (key to state/province abbreviations)
AL      FL      GA      HI      LA      MS      NC      SC      TX      VA


K111 Oak-hickory-pine
K112 Southern mixed forest
K115 Sand pine scrub
K116 Subtropical pine forest

69 Sand pine
70 Longleaf pine
71 Longleaf pine-scrub oak
75 Shortleaf pine
81 Loblolly pine
82 Loblolly pine-hardwood
83 Longleaf pine-slash pine
84 Slash pine
111 South Florida slash pine

808 Sand pine scrub
809 Mixed hardwood and pine
810 Longleaf pine-turkey oak hills
811 South Florida flatwoods
812 North Florida flatwoods
813 Cutthroat seeps
820 Everglades flatwoods

Associated hardwoods on mesic coastal plain sites include southern red oak (Quercus falcata), blackjack oak (Q. marilandica), water oak (Q. nigra), flowering dogwood (Cornus florida), blackgum (Nyssa sylvatica), sweetgum (Liquidambar styraciflua), persimmon (Diospyros virginiana) and sassafras (Sassafras albidum). Associated hardwoods on xeric sandhill sites include turkey oak (Q. laevis), bluejack oak (Q. incana), sand post oak (Q. stellata var. margaretta), and live oak (Q. virginiana) [7].

Associated shrubs include gallberry (Ilex glabra), yaupon (I. vomitoria), large gallberry (I. coriacea), wax-myrtle (Myrica cerifera), shining sumac (Rhus copallina), blueberry (Vaccinium spp.), huckleberry (Gaylussacia spp.), blackberry (Rubus spp.), saw palmetto (Serena repens), sweetbay (Magnolia virginiana), swamp cyrilla (Cyrilla racemiflora), and buckwheat-tree (Cliftonia monophylla) [7].

In longleaf pine's western range, groundcover includes bluestem (Andropogon spp.) and panicum (Panicum spp.). In its eastern range, pineland threeawn or wiregrass (Aristida stricta) is the primary groundcover [7].

The published classifications listing longleaf pine as a dominant or codominant species in community types (cts) are presented below:

Area                         Classification                 Authority

e TX, LA, MS          general veg. cts              Bridges & Orzell 1989
AL                            forest cts                       Golden 1979
SC                            veg. cts                         Nelson 1986
se US; Gulf Coast      general forest cts           Pessin 1933
se US                        general forest cts           Waggoner 1975
NC                            veg. cts                         Wells 1928


SPECIES: Pinus palustris
Longleaf pine forests provide excellent habitat for bobwhite quail, white-tailed deer, wild turkey, and fox squirrel. Sixty-eight species of birds utilize longleaf pine forests [45]. Birds, and mice, squirrels, and other small mammals eat the large seeds. Ants eat germinating seeds, and razorback hogs eat the roots of seedlings [7,54]. Old-growth longleaf pine stands provide nesting habitat for the endangered red-cockaded woodpecker [16].

Nutritional value: Longleaf pine seed is more than 25 percent protein and more than 0.05 percent phosphorus [47].

Longleaf pine is recommended for reforestation of dry, infertile, deep sands in the southeastern United States. Most of these sites were formerly longleaf pine forests but were invaded by scrub oaks (Quercus spp.) after timber harvesting [48]. Longleaf pine is of limited use for rehabilitation of mine spoils in Alabama [50].

Longleaf pine's needles are used for mulch. Resin is used in the naval stores industry for gum turpentine and rosin production [7].

Wood Products: Longleaf pine, a valued timber species, has clear, straight wood with few defects [18]. It was used extensively in the past for timber and ship building. Most virgin stands have now been harvested. Because longleaf pine is not as easy to regenerate as other southern pine timber species, it is not used as extensively as it once was. Longleaf pine's highly desirable wood, however, has stimulated efforts to regenerate it [7,18].

Longleaf pine communities are estimated to have once covered 59 to 87 million acres (24-35 million ha); now only 5 to 10 million acres (2-4 million ha) remain. Of that remaining, most is second growth and in poor condition [40,41]. Because of its timber value and because longleaf pine communities house many endangered plant and animal species, forest managers are attempting to regenerate more longleaf pine communities.

Natural regeneration of longleaf pine is difficult because of poor seed production, heavy seed predation by animals, poor seedling survival, and slow seedling growth. Longleaf pine is best managed with even-aged silviculture using a three-cut shelterwood system [2,5,18,25]. The preparatory cut, 10 years before expected seed crop, should leave a basal area of 60 to 70 square feet per acre (13.8-16.1 sq m/ha). The remaining trees will develop larger crowns and increase seed production. The seed cut, 5 years before the expected seed crop, should leave a basal area of 30 square feet per acre (6.9 sq m/ha). The seedbed should be prepared, usually with fire, when a good seed crop is evident from large numbers of conelets. Seed trees should be removed 1 to 2 years after seedlings are established and before height growth has been initiated [5,25].

The group selection method can be used to naturally regenerate uneven-aged stands. Up to 2 acres (0.8 ha) of trees should be cut so discernible openings are created [2].

Methods for artificial regeneration of longleaf pine are detailed in Rounsaville 1989 [45].

Disease and insects: Longleaf pine is highly resistant to most diseases and insects that infect other southern pines. The main disease of longleaf pine is brown-spot needle blight (Scirrhia acicola). Defoliation suppresses and eventually kills grass-stage seedlings [7]. Infection of seedlings is less severe under a pine overstory than in the open [4]. About 20 percent of seedlings are resistant to brown-spot needle blight [17]. (See Fire Management).

Other diseases include pitch canker (Fusarium moniliforme var. subglutinans), annosus root rot (Heterobasidion annosum), and cone rust (Cronartium strobilinum). Insects that attack longleaf pine include black turpentine beetle (Dendroctonus terebrans), bark beetles (Ips spp.), and seed bugs (Tetyra bipunctata and Leptoglossus corculus), which can decimate a seed crop [7].

Predation: Despite fall germination, which minimizes the time seed lies on the forest floor, predation by birds and small mammals can decimate a seed crop [18].

Weather: Because of the fall germination, low winter temperatures can damage cotyledons. March frosts can destroy flowers. Hurricanes, tornadoes, and lightning cause local damage [7,18].

Other considerations: Moderate cattle grazing has no effect on longleaf survival, but heavy grazing reduces young tree density by 20 percent [54]. Hogs significantly reduce longleaf pine establishment and can cause crop failure [30].


SPECIES: Pinus palustris
Longleaf pine is a long-lived, native, evergreen conifer with scaly bark. Needles are 8 to 18 inches (20-46 cm) long; cones are 6 to 8 inches (15-20 cm) long. Mature trees attain a height of 100 to 120 feet (30.5-36.6 m) and have the potential of living 4 to 5 centuries. The longleaf pine seed is the largest of all southern pines. On good sites, longleaf pine grows an 8- to 12-foot-long (2.4-3.7 m) taproot and extensive lateral roots [7,38,54].


Seed production and dissemination: Longleaf pine is monoecious. It begins producing cones when it reaches about 30 years of age or 10 inches (25 cm) in diameter [18,38]. The best cone producers are 15-inch-diameter (38 cm) open-grown trees. Cones contain, on average, 35 seeds [7]. Longleaf pine masts every 7 to 10 years, but healthy trees will produce a fair to good seed crop every 3 to 4 years [2,37,38]. The winged seeds are dispersed a short distance by wind with 71 percent of the seeds falling within 66 feet (20 m) of the base of the parent tree [7].

Germination and seedling development: Seeds germinate 1 to 2 weeks after seedfall. Germination is epigeal and requires mineral soil. The seed's large size and persistent wing prevent it from penetrating through the litter. Seedlings are stemless after one growing season and this "grass-stage" lasts from 2 to many years [7,18,38]. It may last as long as 20 years if brown-spot needle blight or competition is severe [18,45]. During the grass-stage, the seedling develops an extensive root system, and the root collar increases in diameter. When the root collar diameter approaches 1 inch (2.5 cm) in diameter, height growth begins. An open-grown seedling grows 10 feet (3 m) in 3 years once height growth is initiated [7,37,54]. Branch production is delayed until the seedling reaches 10 to 16 feet (3-5 m) in height [43].

Vegetative reproduction: If grass-stage seedlings are top-killed, they can sprout from the root collar. Once height growth begins, sprouting ability decreases rapidly [7].

Longleaf pine grows in a warm, wet, temperate climate with an annual precipitation of 43 to 69 inches (109-175 cm). The species occupies a wide variety of upland and flatwood sites, but is most common on sandy, infertile, well-drained soils. Soil types include Ultisols, Entisols, and Spodosols. Elevations range from near sea level to 1,970 feet (600 m), although most longleaf pine grows below 660 feet (200 m) [7].

Longleaf pine is intolerant of shade and competition. With frequent fire, uneven-aged pure stands of longleaf pine form parklike savannahs [7,20,37]. Because longleaf pine regenerates in openings created by the death of mature trees, small clusters of trees of the same age are dispersed throughout the stand [43]. In the absence of frequent fire, longleaf pine is replaced by hardwoods and other southern pines [7,54]. Loblolly pine and shortleaf pine will invade and soon dominate a site of grass-stage longleaf pine [11]. Recruitment of longleaf pine ceases 15 years after fire. Invasion by hardwoods accelerates the decline of mature longleaf pine [24].

Longleaf pine is classified as a fire subclimax [18,19,20,45]. Lightning, which historically ignited the frequent fires, is a component of a long-term climatic pattern. As long as there is lightning, longleaf pine can perpetuate itself indefinitely on a site.

Longleaf pine seed develops in a 3-year process. Strobili are initiated during midsummer. Conelets emerge in late winter. Catkins emerge in November, then remain dormant until late winter. Pollination occurs from late February in the South to early April in the North. Fertilization does not occur until the following spring. Cones reach maturity in mid-September to mid-October after their second season of growth. Seed is dispersed from late October to November and the majority of seed falls in 2 to 3 weeks. Seed germinates 1 to 2 weeks later. Primary needles appear soon after germination and secondary needles about 2 months later [7,18].


SPECIES: Pinus palustris
Longleaf pine is classified as fire-resistant [10,36]. It is ideally suited to a high-frequency, low-severity surface fire regime. The natural fire interval is every year to every 5 to 10 years [44]. Most natural fires are caused by lightning and occur in late spring and summer [37,44].

Longleaf pine has many adaptations to fire. The grass-stage seedling is resistant to fire. If top-killed, it sprouts from the root collar. Once the terminal bud develops, it is protected by a moist, dense tuft of needles. As the tuft burns towards the bud from the needle tips, water is vaporized. The steam reflects heat away from the bud and extinguishes the fire [37,38]. The bud also has scales for protection and a silvery pubescence that probably reflects heat [29,37].

During the grass-stage, the seedling invests heavily in a taproot and in root collar size. When height growth is initiated, often the year after a fire, the seedling uses its stored reserves to quickly grow a straight stem with no branches. After one growing season, the terminal bud is usually above the level of the next surface fire [37,38].

The bark becomes thick with age and insulates the cambium from heat. The scaly bark dissipates heat by flaking off as it burns [37,38].

In addition to fire resistant adaptations, longleaf pine has a pyrogenic strategy. Spring and summer fires are beneficial because they reduce competition and expose the mineral soil necessary for seed germination in the fall. Long, resin-filled needles have short persistence and form a highly flammable, well-aerated litter. Resin is also concentrated in the bole and roots of older trees and snags. These trees act as lightning receptors. A smoldering tree can ignite the ground several days or weeks later when the ground litter has dried out. Longleaf pine communities often have a grass understory that readily ignites. [28,37,43]. Because of open stands and high and open crowns, crown fires are rare [43].

FIRE REGIMES : Find 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".

Crown-stored residual colonizer; short-viability seed in on-site cones
Off-site colonizer; seed carried by wind; postfire years one and two


SPECIES: Pinus palustris
Open-grown grass-stage seedlings with root collar diameters smaller than 0.3 inch (0.8 cm) can be killed by light fire [7,29]. Under a pine overstory, light fire can kill seedlings smaller than 0.5 inch (1.3 cm) in diameter, because excess pine litter under the canopy makes the fire hotter [3,18,44]. In a prescribed winter fire in Alabama, 1-year-old seedlings with exposed root collars were more susceptible to fire than seedlings with root collars at or near the soil surface [33]. Larger grass-stage seedlings are highly resistant to fire.

In the height-growth stage, seedlings 1 to 3 feet (0.3-0.9 m) tall are extremely vulnerable to fire [20,29]. If the terminal bud is destroyed, the seedling will die [37]. Once a seedling is about 3.3 feet (1 m) tall, it is likely to survive low-severity ground fires [38]. After the sapling is 10 feet (3 m) tall, it is very fire tolerant [54]. Trees 10 inches (25 cm) in diameter and larger survive all but the most severe fires [10]. A high-severity crown fire kills some mature trees and nearly all trees smaller than 10 inches (25 cm) in diameter [20].

Longleaf pine needles were killed instantly when immersed in water at 147 degrees Fahrenheit (64 deg C) but survived 11 minutes at 126 degrees Fahrenheit (52 deg C) [14].

No entry

Fire can stimulate height-growth initiation of grass-stage seedlings. After three annual spring fires in Louisiana, most grass-stage seedlings had initiated height growth. It is thought that height growth is initiated because fire reduces competition and brown-spot needle blight infection. Late spring or summer fires are more effective at promoting height growth than winter fires [12,13,23]. However, annual fires begun only 1 year after germination stunt height growth [20].

Once a seedling has entered the height-growth stage, fire damage can decrease growth. Annual fires have reduced basal area growth of young longleaf pine by 22 to 44 percent [54]. In Alabama, prescribed biennial fires begun in 14-year-old stands averaging 22 feet (6.7 m) in height and 3.2 inches (8.1 cm) in diameter reduced growth, even though no crown scorch was observed. The impact on growth of biennial fires worsened with time. The season of fire had no effect [6].

Older longleaf pine shows no growth loss if there is little or no needle scorch [29]. Seed production of mature trees is not affected by frequent fire.

Seed will germinate on mineral soil exposed by fire [7].

Trees in regularly burned stands develop a buttressed trunk which results in stump taper [1].

The Fire Case Study Imperata cylindrica in a Florida sandhill longleaf pine community provides information on fuel loads, prescribed fire use, and postfire response of juvenile longleaf pines on cogon grass (Imperata cylindrica)-infested sites and uninfested sites.

Prescribed burning in longleaf pine stands is used to control brown-spot needle blight, stimulate height growth, reduce excess fuel, control understory hardwoods, improve wildlife habitat, thin stands, and prepare a mineral seedbed [18,54].

Fire consumes foliage infected by brown-spot needle blight as well as inoculum in fallen leaves [29,54]. Burning is recommended when infection levels are greater than 20 percent and grass-stage root collars are larger than 0.3 inches (0.8 cm) in diameter or height-growth stage seedlings root collars are greater than 1.5 inches (3.8 cm). If the infection rate is higher than 20 percent, a high percentage of affected seedlings will die from the fire [18,35,45].

Annual spring fires are recommended to initiate height growth once grass-stage seedlings are large enough to withstand fire. In the spring, the green grass keeps the fire cool, and buds are protected by long sheaths of needles. However, grass-stage seedlings grown on poor sites may not tolerate light fire [12]. Once height growth begins, the stand should not be burned for several years and then burned less frequently [23].

Late annual spring fires are recommended to gain control of hardwoods. Summer fires are also effective, but the risk of pine mortality is increased [8]. Hardwoods are susceptible to fire in the late spring and summer because root reserves are low. Once hardwood populations are reduced, winter fire at 5-year intervals maintains longleaf pine stands, and enables a single fire in the spring or summer before seedfall to expose the necessary mineral soil seedbed [18,53].

Although longleaf pine regeneration is rarely excessive [2], a stand can be thinned by fire. In Alabama, a prescribed winter fire thinned a 1-year-old stand from 177,000 seedlings per acre (437,000/ha) to 6,300 per acre (15,600/ha) [33].

Frequent late spring or early summer fires are necessary to recreate the longleaf pine-grassland savannahs that were common in presettlement times [44].


Imperata cylindrica in a Florida sandhill longleaf pine community

Howard, Janet L., compiler. 2005. Imperata cylindrica in a Florida sandhill longleaf pine community. In: Pinus palustris. In: Fire Effects Information System, [Online]. U.S. Department of Agriculture, Forest Service, Rocky Mountain Research Station, Fire Sciences Laboratory (Producer). Available: /database/feis/ [ ].

This Fire Case Study contains information on the following species:

Common name Scientific name
cogon grass Imperata cylindrica
longleaf pine Pinus palustris

This Fire Case Study is based on the following research papers:

Lippincott, Carol L. 2000. Effects of Imperata cylindrica (L.) Beauv. (Cogongrass) invasion on fire regime in Florida Sandhill (USA). Natural Areas Journal. 20(2): 140-149. [57].

Lippincott, Carol L. 1997. Ecological consequences of Imperata cylindrica (cogongrass) invasion in Florida sandhill. Gainesville, FL: University of Florida. 165 p. Dissertation. [58].

The study was conducted in the 16,000 ha Citrus Tract of the Withlacoochee State Forest in west-central peninsular Florida. Withlacoochee State Forest is in Citrus County near the city of Brooksville. The study period was from 1995 to 1996 [58].

Soils on the study site are low-nutrient Entisols derived from marine sand deposits that lack profile development. Mean annual precipitation on Florida sandhills ranges from 1,190 to 1,630 mm/year, with rains mostly occurring from June to September (references cited in Lippincott 2000 [57]).

Study sites were in a longleaf pine savanna with a subcanopy of bluejack oak (Quercus incana), turkey oak (Q. laevis), and sand live oak (Q. geminata). Wax myrtle (Myrica cerifera) and saw-palmetto (Serenoa repens) also occurred in the subcanopy. There were 4 study sites, each with 2 treatment plots (invaded and uninvaded). Invaded and uninvaded plots were adjacent to each other on each of the 4 sites [57,58].

Groundlayer vegetation differed on invaded and uninvaded plots. The ground layer on invaded sites was mostly nonnative cogon grass (Imperata cylindrica). Groundlayer vegetation on uninvaded sites was dominated by native bunchgrasses including pineland threeawn (Aristida stricta), pineywoods dropseed (Sporobolus junceus), narrowleaf silkgrass (Pityopsis graminifolia), and lopsided Indiangrass (Sorghastrum secundum). Summer farewell (Dalea pinnata) was a common forb associate [57].

Cogon grass was intentionally introduced into the Brooksville area in the early 1990s as a forage crop [59]. It was probably introduced in the Citrus Tract from seed-contaminted road fill (Blanchard, as cited in [58]). During the study period, cogon grass occurred in scattered swards in the Citrus Tract. Cogon grass patch size ranged from a few square meters to several hectares [58].

Plant phenology was not described; however, the fire was conducted as a growing-season burn.

Early spring/Moderate severity

The objective of the study was to determine if fuel loads and fire behavior on longleaf pine sandhill sites invaded by cogon grass differed compared to uninvaded longleaf pine sandhill sites. Before burning, fuel load, vertical distribution, horizontal continuity, moisture content, and heat of combustion were compared on invaded and uninvaded sites. After fire, rates of accumulation of postfire fuels were compared on invaded and uninvaded plots.

Longleaf pine juveniles were randomly tagged on burn and no-burn plots before prescribed burning. Fire spread was measured during burning. Fire severity was determined by measuring mortality of tagged juvenile longleaf pines and postfire growth rate of tagged juvenile longleaf pines that survived the fire. Mortality and height and basal area of surviving pines were measured at postfire month 1. Height and basal area of surviving pines were measured again at postfire year 1 [58].

The natural fire regime of longleaf pine forests on Citrus Tract is surface fire at 2- to 8-year intervals, fueled primarily by pine needles, oak leaves, and perennial bunchgrasses including threeawns (Aristida spp.) and pineywoods dropseed (Sporobolus junceus). Lightning-ignited fires were most common during the spring and summer thunderstorm season [57].

The Florida Division of Forestry conducts regular prescribed burning on the Citrus Tract for forest and game management. The area in which study plots were located was last burned 4 years prior to study initiation [58]. Just before this study's prescribed burn, mean moisture contents of live and dead fuels were similar on invaded and uninvaded plots (46.2% ±10.7 and 42.3% ± 12.3, respectively). Mean heat of combustion was slightly higher for native grasses (18.40 kJ/g ± 0.20) compared to cogon grass (18.77 kJ/g ± 0.22). Prescribed fires were conducted early in the growing season (March and April) and ignited in mid-morning as backing fires. Midway through burning, wind shifts caused the 3rd and 4th fires to head. Treatment plot sizes and weather parameters were [58]:

Site Plot size
Season Fire type Wind speed
Relative humidity
Ambient temperature
1 35 x 130 April 1995 backing 8 32 25
2 35 x 145 April 1995 backing 13 56-68 29
3 35 x 40 April 1995 backing/head 16 44-56 24
4 35 x 35 March 1996 backing/head 8 63 22

Prefire fine fuel load was significantly less on native sandhill sites compared to cogon grass sites (P=0.04). From 0 to 0.49 m in height, fine fuel mass did not differ between uninvaded and cogon grass-invaded sites; however, fine mass of fine fuels from 0.50 to 1.50 m was higher (P<0.01) on cogon grass sites [57]. Prefire fuel loads at 3 heights were [58]:

Aboveground height (m)

Fine fuel biomass (g/m²)

Invaded Uninvaded
0 - 0.49 800 630
0.50 - 0.99 275 75
1.00 - 1.50 25 ----

Mean heat of combustion was slightly higher for native fuels (P<0.01). Instantaneous maximum fire temperature at 3 heights was measured with temperature-indicating paints on steel poles. There was a significant difference (P<0.05) in mean maximum temperature between prescribed fires in cogon grass (260.9 ± 13.7 °C) and native sandhill (218.3 ± 14.5 °C) sites [57]. Fuel load ratios and fire temperatures by height were [58]:

Aboveground fuel height Fuel biomass ratio
Maximum temperature
( °C)
Invaded Uninvaded
ground level ---- 275 250
0.5 m 4.5:1 245 195
1.5 m 6:1 250 175

Fire rate of spread was similar on invaded and uninvaded plots (P=0.75). Fireline intensity was also similar on invaded vs. uninvaded plots (P=0.22) [58]:

Site Fire type Rate of spread (m/s) Intensity (kW/m)
Invaded Uninvaded Invaded Uninvaded
1 backing 0.0185 0.0235  395.95  341.41
2 backing 0.0208 0.0195  445.18  283.30
3 head 0.1300 0.1300 2782.37 1888.64
4 head 0.1458 0.0280 3120.54  406.78

Cogon grass changed fine fuel characteristics that determine the fire regime of Florida sandhill plant communities. At postfire month 5, significantly more fine fuels had accumulated on cogon grass sites compared to native sandhill sites (P<0.01). Cogon grass sites had 90% less bare ground, so fine fuels were more evenly distributed than fuels on uninvaded sites. At time of burning, cogon grass had 50% more fine fuel by weight compared to native herbaceous fuels, so cogon grass reached higher temperatures than native herbs. Cogon grass fuels averaged 50 °C hotter at 0.5 m above ground, and 73 °C hotter at 1.5 m, compared to native sandhill herbaceous fuels. Cogon grass recovered quickly after fire. At postfire month 3, cogon grass sites had 100% more fine fuels than native sandhill sites; 86% more at postfire month 6; and 50% more at postfire month 14. With twice as much fuel after only a few months' growth, fire in cogon grass-infested sites could ignite and spread frequently in the absence of fire management [57].

Fire mortality of longleaf pine juveniles was higher on cogon grass-invaded plots, and the postfire growth rate of surviving longleaf pine juveniles was decreased on invaded plots. Juvenile longleaf pine size classes were indicated by height. Longleaf pine mortality on invaded and uninvaded plots was [57,58]:

Juvenile size class Height (m)

Mortality (%)

Invaded Uninvaded
Small 0-0.49 32 23
Medium 0.50-0.99 80 49
Large 1.00-1.50 84 76

At postfire year 1, growth of surviving small juvenile longleaf pines was significantly less on invaded vs. uninvaded plots (P<0.01). Median increase of pines in the smallest size class was 21% vs. 50%, respectively [58]. Poor growth in small longleaf pine juveniles was probably due to competitive interference by cogon grass, rather than direct fire effects to small longleaf pines [57]. (See longleaf pine's Fire Ecology section for discussion on fire effects to longleaf pine juveniles). Height gains for medium- and large-sized longleaf pine juveniles were similar on invaded and uninvaded (P=0.86). For all size classes, stem diameter growth of longleaf pine juveniles was not significantly different on invaded and uninvaded plots [58].

Although cogon grass increases fire mortality of longleaf pine seedlings, mature longleaf pines may not be directly affected by cogon grass presence. In this study, growth of longleaf pines greater than 10.4 cm dbh was not slowed by cogon grass [57].

Without management, fire in longleaf pine sandhill communities has the potential to ignite and spread more quickly on cogon grass-invaded sites compared to uninvaded sites. Presence of cogon grass significantly affected fine-fuel load, changed fuel structure, and increased fire temperatures (P<0.05).

Cogon grass-invaded plots had 50% more fine fuel biomass than uninvaded plots prior to burning. Before burning, invaded plots had a significantly greater (P<0.01) fine-fuel load (mean =1,163 g/m² ± 285 g/m²) compared to uninvaded plots (mean = 177 g/m² ± 2297 g/m²). Structurally, fine fuels on invaded plots were generally taller than on uninvaded plots. Fine-fuel loads between 0.4 and 1.51 m in height were significantly greater on invaded plots (P<0.01). In contrast, fine-fuel loads less than 0.50 m in height were similar on invaded and uninvaded plots (mean =795 g/m² and 668 g/m², respectively; P<0.07). Horizontally, fine fuels were significantly (P=0.04) more continuous on invaded vs. uninvaded plots, with 3.0% bare ground on invaded plots and 0.3% bare ground on uninvaded plots. Fuels on invaded plots were distributed significantly higher above ground: 27% of total fuels were 0.5 m high on invaded plots compared to only 8% on uninvaded plots. Consequently, invaded plots produced significantly higher maximum fire temperatures compared to uninvaded plots (260.9 °C vs. 218.3 °C, P=0.40), and fires were more patchy on uninvaded plots. Fire temperatures in cogon grass reached a maximum of 458 °C on some strips at all aboveground heights measured. After fire, fine fuels accumulated more quickly on invaded plots [57,58].

These mortality data and instantaneous maximum temperature measurements at given points suggest that longleaf pine juveniles may succumb to cogon grass-fueled fires [58]. Additional data on fire duration (e.g., Jacoby and others [68]) will help determine direct fire effects of cogon grass fuels on longleaf pine juveniles. Rapid growth out of the "grass stage" of  growth gives juvenile longleaf pines protection from fire. However, this study showed that young longleaf pines in the 0.5-1 m height class are vulnerable to fire damage on cogon grass sites, which have more fuels and higher fire temperatures compared to sites with native bunchgrass fuels [58]. Koskela and others [78] had similar findings in a Sumatran pine (Pinus merkusii)/cogon grassland of northern Thailand. As a juvenile, Sumatran pine has a "grass growth" stage similar to that of longleaf pine. Juvenile Sumatran pines were killed by frequent fires fueled by cogon grass [78].

Cogon grass can alter longleaf pine community structure and consequently, its fire regime and level of diversity. As a fast-growing, rhizomatous grass that is supplanting slow-growing native bunchgrasses, cogon grass-invaded sites have higher fuels loads, greater horizontal and vertical fuel continuity, and potentially greater flame heights compared to sites with native herbaceous ground layers. In this study, overall understory plant diversity was lower on cogon grass-infested sites compared to uninfested sandhill sites [86]. At postfire month 3, cogon grass sites had over 100% more fine fuels compared to uninvaded sites (P<0.01). Fuel accumulations at 6 and 14 postfire months were 86% and 50% more, respectively, on invaded compared to uninvaded plots. Rapid growth and nonbunching habit of cogon grass can increase fire severity, continuity, spread, and frequency in longleaf pine sandhill habitats, thereby increasing fire mortality of young longleaf pines and reducing habitat quality for native organisms adapted to longleaf pine/bunchgrass habitats [58].

Pinus palustris: References

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