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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) .
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 .
The published classifications listing longleaf pine as a dominant or codominant species in community types (cts) are presented below:Area Classification Authority
Nutritional value: Longleaf pine seed is more than 25 percent protein and more than 0.05 percent phosphorus .VALUE FOR REHABILITATION OF DISTURBED SITES:
Wood Products: Longleaf pine, a valued timber species, has clear, straight wood with few defects . 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].OTHER MANAGEMENT CONSIDERATIONS:
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 .
Methods for artificial regeneration of longleaf pine are detailed in Rounsaville 1989 .
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 . Infection of seedlings is less severe under a pine overstory than in the open . About 20 percent of seedlings are resistant to brown-spot needle blight . (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 .
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 .
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 . Hogs significantly reduce longleaf pine establishment and can cause crop failure .
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 .
Vegetative reproduction: If grass-stage seedlings are top-killed, they can sprout from the root collar. Once height growth begins, sprouting ability decreases rapidly .SITE CHARACTERISTICS:
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.SEASONAL DEVELOPMENT:
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 .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".
POSTFIRE REGENERATION STRATEGY :
Crown-stored residual colonizer; short-viability seed in on-site cones
Off-site colonizer; seed carried by wind; postfire years one and two
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 . Once a seedling is about 3.3 feet (1 m) tall, it is likely to survive low-severity ground fires . After the sapling is 10 feet (3 m) tall, it is very fire tolerant . Trees 10 inches (25 cm) in diameter and larger survive all but the most severe fires . A high-severity crown fire kills some mature trees and nearly all trees smaller than 10 inches (25 cm) in diameter .
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) .DISCUSSION AND QUALIFICATION OF FIRE EFFECT:
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 . 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 .
Older longleaf pine shows no growth loss if there is little or no needle scorch . Seed production of mature trees is not affected by frequent fire.
Seed will germinate on mineral soil exposed by fire .
Trees in regularly burned stands develop a buttressed trunk which results in stump taper .DISCUSSION AND QUALIFICATION OF PLANT RESPONSE:
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 . Once height growth begins, the stand should not be burned for several years and then burned less frequently .
Late annual spring fires are recommended to gain control of hardwoods. Summer fires are also effective, but the risk of pine mortality is increased . 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 , 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) .Frequent late spring or early summer fires are necessary to recreate the longleaf pine-grassland savannahs that were common in presettlement times .
|Common name||Scientific name|
|cogon grass||Imperata cylindrica|
|longleaf pine||Pinus palustris|
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. .
Lippincott, Carol L. 1997. Ecological consequences of Imperata cylindrica (cogongrass) invasion in Florida sandhill. Gainesville, FL: University of Florida. 165 p. Dissertation. .STUDY LOCATION:
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 .
Cogon grass was intentionally introduced into the Brooksville area in the early 1990s as a forage crop . It was probably introduced in the Citrus Tract from seed-contaminted road fill (Blanchard, as cited in ). 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 .PLANT PHENOLOGY
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 .
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 .
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 . 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 :
|Season||Fire type||Wind speed
|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 . Prefire fuel loads at 3 heights were :
Aboveground height (m)
Fine fuel biomass (g/m²)
|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 . Fuel load ratios and fire temperatures by height were :
|Aboveground fuel height||Fuel biomass ratio
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) :
|Site||Fire type||Rate of spread (m/s)||Intensity (kW/m)|
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)||
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 . 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 . (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 .
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 .FIRE MANAGEMENT IMPLICATIONS:
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 . Additional data on fire duration (e.g., Jacoby and others ) 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 . Koskela and others  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 .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 . 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 .
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