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Imperata brasiliensis, I. cylindrica

• INTRODUCTORY
• DISTRIBUTION AND OCCURRENCE
• BOTANICAL AND ECOLOGICAL CHARACTERISTICS
• FIRE ECOLOGY
• FIRE EFFECTS
• FIRE CASE STUDIES
• MANAGEMENT CONSIDERATIONS
• REFERENCES

INTRODUCTORY

AUTHORSHIP AND CITATION FEIS ABBREVIATION SYNONYMS NRCS PLANT CODE COMMON NAMES TAXONOMY LIFE FORM FEDERAL LEGAL STATUS OTHER STATUS
	Cogongrass stand. Photo by Kazuo Yamasaki.

The scientific name of cogongrass is I. cylindrica (L.) Beauv. (Poaceae) [9,25,43,64,72,105,173]. Some authorities recognize 5 varieties of cogongrass; according to that treatment, I. c. var. major (Nees) CE Hubb. is the entity found in North America [64,133]. Gabel (within [9]),[43] does not recognize varieties of cogongrass.

Brazilian satintail and cogongrass are morphologically and genetically very similar, and their hybrids produce fertile offspring [57,133,165]. Hybridization, introgression, and overlapping morphological characters often cause taxonomic confusion between the 2 species, especially in North America. Some systematists consider the 2 species synonymous [25,57]. Hall [57] suggests that Brazilian satintail be classified as an infrataxon within I. cylindrica. Gabel [9,43] separates the taxa as 2 distinct species based upon continents of origin and morphological, cytological, and genetic attributes. This review treats Brazilian satintail and cogongrass as 2 distinct species.

Because there is little English-language literature currently available on Brazilian satintail, this review provides information mostly on cogongrass. Pertinent information on Brazilian satintail is included whenever possible. Given the taxonomic status of Imperata in North America, information included in this review may apply to both species; however, further research is needed to be certain the 2 taxa respond similarly to fire and control treatments.

DISTRIBUTION AND OCCURRENCE

• GENERAL DISTRIBUTION
• ECOSYSTEMS
• STATES/PROVINCES
• BLM PHYSIOGRAPHIC REGIONS
• KUCHLER PLANT ASSOCIATIONS
• SAF COVER TYPES
• SRM (RANGELAND) COVER TYPES
• HABITAT TYPES AND PLANT COMMUNITIES

Cogongrass is native to Korea, Japan, China, India, and tropical eastern Africa [37,64,105]. It is nonnative and invasive throughout other tropical regions of the world. In North America it occurs along the Gulf Coast from Mexico east to South Carolina [4,72]. In the United States it is most common in Mississippi, coastal Alabama, and Florida [9]. Hitchcock [61] listed cogongrass as present in Oregon in 1950, although it has not been collected in Oregon for decades. There were 2 known locations of cogongrass introduction in the United States: 1 from Japan to Alabama in 1912, as packing material in a shipment of Unshu orange (Citrus reticulata) trees; and another from the Philippines to Mississippi in 1921, as a possible forage grass [33,44,142,143]. More than 1,000 acres (400 ha) of cogongrass were planted for livestock forage and soil stabilization in Florida the late 1930s and 1940s [32,133].

Grass Manual on the Web provides distributional maps of Brazilian satintail andcogongrass. It is commonly assumed that cogongrass is the more common of the 2 species; however Brazilian satintail or Brazilian satintail × cogongrass hybrid swarms may be misidentified as cogongrass [86,142]. Distributions of Brazilian satintail and Brazilian satintail × cogongrass hybrids may be more extensive in the Southeast than is currently known [44]. The 2 species occur in similar habitats in the Southeast [37,64]. The following lists give biogeographic classifications where Brazilian satintail and cogongrass are known to be present or invasive. These lists may not be exhaustive.

Details of Brazilian satintail communities of South America are also limited. In Peru, Brazilian satintail dominates montane savannas. Copperleaf (Acalypha spp.), muttonwood (Rapanea spp.), speedwell (Veronica spp.), and false-willow (Baccharis spp.) are dominant woody genera; bracken fern (Pteridium aquilinum) often codominates on Brazilian satintail grassland areas. Scott [128] lists associated plant species on Brazilian satintail-dominated savannas of eastern Peru.

Cogongrass occurs in southeastern pine and oak-pine communities that experience frequent fire (see Cogongrass in North America for further details). It is most common in the ground layer of mesic longleaf pine (Pinus palustris) savannas [14]. Oaks including blackjack oak (Q. marilandica), turkey oak (Q. laevis), and southern red oak (Q. falcata) are often frequent in the overstory. Common shrub associates of cogongrass include persimmon (Diospyros virginiana), black highbush blueberry (Vaccinium fuscatum), dwarf huckleberry (Gaylussacia dumosa), and bitter gallberry (Ilex glabra). Common groundlayer associates include big bluestem (Andropogon gerardii), paintbrush (A. tenerius), Beyrich threeawn (Aristida beyrichiana), golden colicroot (Aletris aurea), and roundleaf thoroughroot (Eupatorium rotundifolium) [109]. Cogongrass occurs in south Florida slash pine/firegrass (Pinus elliottii var. densa/Andropogon cabanisii) savannas of Everglades National Park. Brazilian peppertree (Schinus terebinthifolius) and silkreed (Neyraudia reynaudiana) are other nonnative invasive associates inventoried on Everglades savannas. Cogongrass dominates some grassland sites in the Everglades [113].

In Puerto Rico, cogongrass occurs in early seral bracatinga (Mimosa scabrella) forests. Leandra (Leandra australis) and cappel (Palicourea spp.) also occur in the overstory. Groundlayer associates include hemlock-rosette grass (Dichanthelium sabulorum) and flatsedge (Cyperus hermaphroditus) [54].

BOTANICAL AND ECOLOGICAL CHARACTERISTICS

• GENERAL BOTANICAL CHARACTERISTICS
• RAUNKIAER LIFE FORM
• REGENERATION PROCESSES
• SITE CHARACTERISTICS
• SUCCESSIONAL STATUS
• SEASONAL DEVELOPMENT

Brazilian satintail is lesser known, and hence more poorly described, in the United States compared to cogongrass. It has slender, erect culms from 14 to 29 inches (36-74 cm) tall. Leaves are mostly basal and about 5 to 13 mm wide. The inflorescence is a 3- to 8-inch (7-20 cm), terminal panicle [163]; the fruit is a caryopsis. Brazilian satintail is rhizomatous, with a mat-like growth form [43,163].

Cogongrass grows to 3 feet (1 m) in height [25,105]. Leaves are mostly basal, growing from the rhizomes. Basal leaves are 0.4 to 0.8 inch (1-2 cm) wide [43]. A few small upper leaves occur on the pedestal [25,105]. The leaves have a characteristic white midrib that is set off-center. Being high in silica [26], cogongrass leaves are coarse in texture [26,160]. The inflorescence is a dense, 4- to 8-inch (10-20 cm) panicle of paired spikelets. Spikelets are unawned with long (~12 mm), silky hairs [25,105]. The seeds are small (1-1.3 mm long) [74,75].

The root system is fibrous. Cogongrass rhizomes are "tough and scaly," with short internodes forming a dense underground mat. Cogongrass rhizomes develop in 2 stages: primary seedling rhizomes, and secondary rhizomes that sprout from seedling rhizomes [43]. Rhizome and root depths vary with substrate. In central Florida, Gaffney [43] found cogongrass rhizomes were restricted to the top 4 to 6 inches (10-15 cm) of soil on a phosphate mine site, but grew down to 30 inches (80 cm) below ground on a clay settling pond site [43]. In Southeast Asia, rhizomes typically occur 4 to 20 inches (10-40 cm) below ground and form dense, extensive layers. Some rhizomes grow as deep as 3 feet (1 m) [8,100]. Cogongrass's growth habit is loose to clumped, compacted aerial stems arising from the dense rhizome mat [35,43]. Dense stands may form monocultures [43,87].

Brazilian satintail and cogongrass are both nonnative, rhizomatous perennial grasses that are similar in appearance. They are primarily distinguished between one another by stamen numbers: Brazilian satintail usually has 1 stamen/flower, and cogongrass has 2 stamens/flower [43,64,106]. Other distinguishing characteristics include Brazilian satintail's relatively shorter spikelets (<3.5 mm) and narrower culm leaves (<5 mm) compared to cogongrass's spikelets and leaves [3]. These characteristics overlap [43,86], however, and it is likely that the 2 grasses have been misidentified in the Southeast [86]. Identification is further confounded by Brazilian satintail × cogongrass hybridization in the Southeast, the extent of which is unknown [165].

Cogongrass reproduces from seed, rhizome expansion, and rhizome fragments [43,86]. Both seed and rhizome regeneration are important in its spread. Seed reproduction allows for long-distance dispersal and colonization, whereas rhizome spread is the primary means of population expansion [56,64]. Transported rhizome fragments also contribute to its long-distance dispersal and colonization [86].

Breeding system: Cogongrass is outcrossing [43,50,125,133]. Clonal populations show low or no fertility [94]. Imperata cylindrica var. major shows considerable diversity in reproductive morphology and physiology in Asia ([15] and references therein),[124,146]. Studies in central and northern Florida suggested a high degree of genetic variability among cogongrass populations. Populations with low genetic diversity tended to have low seed viability, while populations with high genetic diversity had high seed viability. It is not known whether low seed viability was due to inability to outcross, poor environmental conditions, or other factors. The authors concluded that successful outcrossing was low in most cogongrass populations, but higher rates of genetic diversity and fecundity could be expected as southeastern populations expand and outcross [133].

Pollination: Cogongrass is pollinated by wind [94,133].

Flower production: Cogongrass flower production is highly variable. Some researchers report cogongrass as highly productive [43], but flowering is often sporadic, ranging from none to frequent flowering within and among populations [34,43,106,170]. In a common garden study using Malaysian collections, some cogongrass populations frequently produced flowers; others never produced flowers (but spread vegetatively); while most produced flowers only after mowing disturbance [125]. Disturbances including nitrogen amendment, slashing, burning, defoliation, and grazing may trigger cogongrass flowering [43,63]. However, Shilling and others [133] found consistent flowering in 11 Florida cogongrass populations, none of which were disturbed. Field and greenhouse studies suggest that cogongrass flowering is not photoperiod-dependent [133].

Seed production and seed viability likewise vary widely among populations. A Florida study found that geographically isolated cogongrass populations did not produce seed, but plants within the population produced fertile seeds when cross-pollinated with pollen from another population [94]. Saijise [124] found a mean of 700 seeds/panicle on cogongrass plants in the Philippines. A spikelet count in Florida showed a mean of 363 ± 47.5 spikelets/panicle. Actual production was higher because some spikelets had shattered prior to data collection [133]. A Malaysian study found heavy flower production followed by low seed set [125]. Preliminary investigations in Florida found flowers growing under stressful conditions rarely produced seed, so cogongrass has sometimes been labeled as a poor seed  producer [37,124]. However, later research showed cogongrass can produce seed prolifically, even after disturbance [94,133]. Fire, tillage, mowing, and cold stress may stimulate cogongrass flower and seed production [124].

Seed/rhizome dispersal: Cogongrass seed is spread by wind. The seeds are small and light weight, with long, hairy plumes aiding wind carriage [43,94,133,164]. Cogongrass seeds may drift 15 miles (20 km) in open country [64]. Shilling and others [133] showed that wind can disperse cogongrass spikelets up to 360 feet (110 m) from the parent plant. Cogongrass spread in Alabama from 1973 to 1985 was apparently due to northeasterly prevailing winds from the Gulf of Mexico blowing seeds up Interstate 65 [164,165].

Roads and road construction are important corridors for cogongrass dispersal [17,169]. Rhizomes are transported by machinery and fill dirt during construction [43,107]. Most long-distance dispersal of cogongrass is probably from inadvertent human transport of rhizomes and seeds [86]. Willard and others [169,170] speculated that cogongrass spread in Florida was mostly from transporting soil contaminated with cogongrass propagules.

Seed banking: Cogongrass seed is short lived, generally remaining viable in the soil for about 1 year [50]. Viability of seeds stored in a laboratory steadily decreased over 13 months [34]. Field studies in Asia show a maximum seed life of 16 months [124,125].

Germination: Cogongrass seeds are not dormant and do not require stratification. They germinate 1 to 4 weeks after ripening [8,34,124,125,133]. Shilling and others [133] found that with 11 Florida cogongrass populations, seeds began germinating within 7 days of harvest, with 94% germination by day 14. Seed viability is variable. Seed collected from 9 sites in central Florida showed high variability in germination rate between sites, with viability ranging from 0% to 100% [133]. An Alabama study found 80% to 95% seed viability [34]; another study found 0% germination in Mississippi and 20% in Florida in the same year [64]. Across years in a single population, an Alabama study found 4% germination in 1970 and 70% germination in 1972 [32].

In the laboratory, cogongrass seed collected in Alabama germinated at temperatures from 77 °F to 95 °F (25 °C-35 °C), with best germination at 86 °F (30 °C). Light increased germination time and rate [34]. A Philippine study also found high germination (>80%) in open areas [124]. Light and soil fertility interactions may affect germination. In Florida, seeds germinated with light did not show an increased germination rate when fertilized with potassium nitrate solution; however, seed germinated in the dark had highest germination rate with addition of potassium nitrate [34].

Seedling establishment: Seedlings establish best on open, disturbed areas [8]. In a greenhouse study conducted on seed bank samples collected over 2 years in Polk County, Florida, cogongrass seed emerged over a 3-month period. Seedling density averaged 1.9 ± 0.48 seedlings/m². There was no significant difference (P=0.78) in seedling emergence between collection years, but emergence differed significantly (P=0.001) with month of soil collection. Best emergence occurred in samples collected from April to June, particularly samples collected in May. Another emergence spike occurred in samples collected in December and January. Seedlings did not emerge from soil samples collected in other months [133]. Cogongrass seedlings tend to emerge in clumps, reflecting the tendency of spikelets to disperse in clumps [35]. Seedling mortality is generally high, with about 20% of emergents surviving to produce seed. Risk of mortality probably lessens when seedlings sprout rhizomes [133].

For established populations, asexual regeneration from rhizomes is cogongrass's primary method of expansion [7,43]. Kushwaha and others [82] reported that on old fields in India, cogongrass regenerated from mostly seed on recently burned, clipped, or abandoned plots, but regenerated only from rhizomes on 3- to 5-year-old fallows. On 2 study sites in Mississippi, cogongrass spread into longleaf pine savannas from infested roadsides. Spread was almost entirely from rhizomes. Rhizome spread slowed, but did not stop, as the populations expanded into interior savannas [165]. Eussen [37] reported that cogongrass can produce 350 rhizomes in 6 weeks, and cover 4 m² in 11 weeks.

Regenerative capacity of cogongrass rhizomes is linked to stem age, length, thickness, and number of large buds. Only old ("2nd generation" or rhizomes arising from rhizome buds) rhizomes can sprout and grow roots [43]. Rhizomes sprout readily after mowing, grazing, or burning removes top-growth [8]. A low root:rhizome ratio aids in rapid regrowth after fire or mowing [124]. In a growth chamber study, Ayeni and Duke [8] found old, large rhizome segments showed best stem sprouting and biomass gain compared to small, younger rhizome segments. Soerjani [136] found rhizome sprouting ability was not restricted by bud size, position on the node, internode length, or node diameter. In greenhouse and laboratory experiments, potted rhizomes buried deeper than 3 to 8 inches (8-20 cm) below the soil surface show poor sprouting ability [37,165].

Possibly because of low intrapopulation genetic diversity and inability to outcross, isolated cogongrass populations reproduce mostly or entirely by clonal expansion from rhizomes. Although rhizome growth is rapid, populations that reproduce mostly by cloning probably have lower overall rates of expansion compared to populations that reproduce from both seed and rhizomes. Overall rates of invasion probably increase when seed-reproducing cogongrass populations expand into and cross-pollinate with previously rhizome-expanding populations [86].

Growth: Ramet growth is considerably faster than seedling growth. In the greenhouse, Shilling and others [133] found plant height, leaf number, and biomass were significantly greater (P<0.001) in plants grown from broken rhizome fragments compared to seedlings. Rhizome fragments produced new secondary rhizomes within 4 weeks, while seedlings took 12 weeks to produce primary rhizomes. Cogongrass rhizomes can produce 350 shoots in 6 weeks and cover 4 m² in 11 weeks [37]. In the greenhouse, cogongrass seedlings produced primary rhizomes 4 weeks after emergence [125]. In Marion County, Florida, 3- to 4-month-old, wild seedlings were observed in the 5-leaf stage in October, and seedlings had formed roots and primary rhizomes. Secondary rhizomes were not yet present [133].

Growth may vary among cogongrass populations. In a greenhouse experiment, plants grown from rhizomes collected in Mississippi (2 populations of Philippine origin) were significantly smaller (P<0.05) than plants grown from Alabama rhizomes (2 populations of Japanese origin). In the growth chamber, ideal day/night temperatures and photoperiod across cogongrass populations were 84/73 °F (29/22 °C) and 16 hours, respectively [106].

Biomass of fully developed cogongrass stands is considerable. A New Guinea study found cogongrass's annual dry-matter production averaged 23 Mg/ha [58]. In a Java field study, Soerjani [136] determined that undisturbed cogongrasslands contained approximately 3 to 6 million shoots/ha, 7 to 18 tonnes of leaves/ha, and 3 to 11 tonnes of rhizomes/ha.

Cogongrass tolerates a wide range of site conditions across its worldwide range. It is drought tolerant, and somewhat shade and salt tolerant [70]. In its native lands of Asia and Africa, it grows on arid desert sands, river margins, and swamps [134]. Describing cogongrass in Indonesia, Terry and others [146] wrote "unlike most other plants ... I. cylindrica can tolerate drought, waterlogging, fire, cultivation and short-term shade ... at a single site." Imperata cylindrica var. major, the variety in North America, commonly occupies a wide variety of habitats in Asia including grasslands, deforested areas, old fields, cultivated fields, riparian areas, and disturbed sites such as roadsides. Other varieties have narrower habitat requirements and are less ubiquitous in their native ranges [37]. Hubbard [64] speculated that when Southeast Asian lands were still pristine, cogongrass may have been restricted to arid, relatively sterile, or heavy clay soils. In the United States, cogongrass is common on disturbed sites such as roadsides, mine spoils, pastures, agricultural lands, plantations, and early seral pine forests [43,90,173]. It also occurs on relatively undisturbed sites including wet and dry bottomland [137] and old-growth longleaf pine forests [155].

Soils: Cogongrass is sometime mistaken as an indicator of "degraded" lands with nutrient-poor soils. Although common on nutrient-poor soils (Ultisols and Oxisols) that native southeastern grasses cannot tolerate, it also occurs on soils of moderate to high fertility (Inceptisols and Andisols) [43,46,100]. Cogongrass tolerates a wide range of soil textures from coarse sands to heavy clays [43]. Soils in cogongrass's native Asia are often highly leached, with low pH, fertility, and organic matter [124]; however, cogongrass is not limited to nutrient-poor soils in Asia [100]. About 65% of cogongrass in Asia grows on strongly acidic soils (pH≤5.0) with a topsoil layer of 4 to 6 inches (10-15 cm) [19]. Nigerian researchers report cogongrass growing on slightly acid to neutral soils [130]. Best growth in North America occurs on moist, very strongly acid (pH 3.0-4.7) clay soils  [43,64,124]; however, cogongrass often grows on clay soils of neutral pH in Florida [43,64]. On poor soils, cogongrass's ability to form monotypic stands in the southeastern United States is due in part to its ability to outcompete native herbs for space, light, water, and nutrients [12,26,38,48,86]. Cogongrass forms thick swards that cover thousands of hectares on abandoned phosphate mines dug in the heavy clay soils of  Polk County, Florida [86].

Elevation: Worldwide, cogongrass is most common at elevations from sea level to 3,000 feet (1,000 m) elevation [19]. Elevational ranges for cogongrass in the United States were not reported as of this writing (2005).

Climate: Cogongrass is native to regions of wet-tropical and subtropical Asia and Africa where annual rainfall averages between 40 to 100 inches (1,000-2,500 mm) ([100] and references therein),[134]. Worldwide, cogongrass is most invasive in wet tropical and subtropical areas receiving 30 to 200 inches (750-5,000 mm) of annual rainfall [17]. It tolerates hot temperatures but is sensitive to cold [164,165]. It is limited to latitudes below 45° in both hemispheres ([17] and references therein). Rhizomes cannot recover when subject to temperatures of approximately 14 °F (-10 °C). Cogongrass survived winter temperatures that dropped to 7 °F (-14 °C) in Alabama [165], but did not survive winter temperatures of 18 °F (-8 °C) in Mississippi [64].

Moisture regime: Cogongrass tolerates both xeric and flooded soils, but cannot tolerate soils that are waterlogged for long periods of time [116]. Along the Nile River in Egypt, cogongrass is associated with high-moisture, high-salinity sites [129]. It grows up to the edges of standing water in Florida [70], but does not invade continually flooded sites [28]. In a greenhouse experiment, cogongrass germinants were intolerant of soil inundation and became increasingly tolerant of saturated soils as the plants matured. The authors concluded that soil inundation in early spring could limit cogongrass seedling establishment [74].

Cogongrass is an early seral species. In both native and nonnative habitats, it depends on fire or other frequent disturbance to maintain dominance [37,82]. In tropical and subtropical ecosystems of Asia, cogongrass ordinarily declines and disappears with postdisturbance canopy closure [37,81,144]. It does best in full sun. Cogongrass cannot tolerate deep shade [15,100], but can survive in the moderate shade of savannas [63,64]. It establishes in forest gaps of all sizes. In longleaf pine/wiregrass (Aristida spp.) wet savannas of Grand Bay National Wildlife Refuge, Mississippi, cogongrass was experimentally seeded-in on small- (10 cm in diameter; 66% of full sunlight) to large-diameter (100 cm; 89% full sunlight) gaps created by herbicide spraying. Cogongrass germination averaged 40% across treatments. Seedling survivorship did not differ among gap sizes (P>0.05) [75]. For information on cogongrass succession in fire-created gaps, see Discussion and Qualification of Plant Response.

In its native Southeast Asia, cogongrasslands are an early successional stage that develops following a stand-replacement event, usually fire [37,104,114]. Cogongrass is common in tropical old-field succession, with or without fire, but shifting (slash-and-burn) agriculture has greatly increased its occurrence in Asia and Africa. In its native lands, cogongrass has formed extensive swards in areas that were once forested [85,174]. In Asia, cogongrass lands succeed to tropical forest if succession is not interrupted by slash-and-burn agriculture [10,42,104]. Postdisturbance tropical forest development can be blocked by lack of sprouting trees, seed bank depletion, lack of off-site seed dispersal, and/or depletion of soil nutrients [42,100]. Several cycles of sand-replacement disturbance are usually needed for tropical forest-to-grassland conversion [37,100]. In northeastern India, cogongrass colonized burned fields for up to 6 years after burning. Importance value of cogongrass peaked at 74.5 in study plots at postfire year 3, when cogongrass was the most important plant species present. After 6 postfire years, Kashia pine and broadleaved trees began establishing and shading out cogongrass, sticky snakeroot, and other early successional herbs [97]. Without frequent disturbances, cogongrass usually becomes less important as succession advances. On old fields in India, cogongrass was successionally eliminated on plots undisturbed for more than 5 years [82]

Cogongrass also occurs after nonanthropogenic disturbances. It was recorded as a pioneering species on Krakatau, Indonesia, 14 years after the 1883 volcanic eruption. The nearest point of possible seed dispersal was 25 miles (40 km) away (references in  [64]). On coastal Japan, cogongrass dominates stabilizing sand dunes, becoming less common on either unstable or stable dunes [89]. In Puerto Rico, cogongrass was 1 of the most frequent pioneering herbaceous species in bracatinga forests disturbed by hurricanes [54].

Worldwide, cogongrass shows variable phenological development depending upon climate and population genetics. Cogongrass flowers from May to June in its native Japan [105]. Generally, populations growing in mediterranean climates tend to flower in spring and summer, while populations in tropical and subtropical areas (including Florida) tend to flower year-round [17]. On foothill slopes of the western Himalayas in India, cogongrass germinated in March to April; grew vegetatively from May to June; flowered from July to mid-August; fruited from late August to early September; produced ripe fruit through September; and was dormant from October through December [1].

In Florida, cogongrass flowering peaks in late winter to spring (March-May) [25,173]. In a Polk County study, cogongrass flowered in November and December and again in March and April in both years of a 2-year study. Flowering time was consistent within a population, but varied across populations [133].

FIRE ECOLOGY

• FIRE ECOLOGY OR ADAPTATIONS
• POSTFIRE REGENERATION STRATEGY

Brazilian satintail sprouts from rhizomes after top-kill [128]. Postfire seedling establishment is also likely. Mass flowering has been noted in Brazilian satintail following fires in Brazil [55,93].

Cogongrass sprouts from rhizomes after top-kill by fire [64,97,127,144]. It also establishes from seed, usually blown in from off-site [97]. Regrowth from rhizomes is rapid [8,124], and frequent fire favors cogongrass over associated species worldwide [15,97,100,160,161]. Fire is so important to cogongrass's ecology that relative response to fire is one of the characteristics used to distinguish between its varieties [64].

Fuels: Descriptions of fuel characteristics and fuel loads in Brazilian satintail grasslands were not available as of 2005.

Cogongrass invasion changes fuel properties in pinelands of the southeastern United States. As a tall, rhizomatous grass on sites historically dominated by bunchgrasses, cogongrass produces more standing biomass and litter than native bunchgrasses. Thus, it increases fuel loads and horizontal and vertical continuity of fuels [87].

Fuel load estimates are needed for cogongrass-dominated sites in the United States. Fuel load measurements in native cogongrasslands may serve as a first step for estimating fuel loads in the southeastern United States. Pickford and others [111] conducted fuel sampling in burned and unburned forest-mangrove (Acacia mangium)/cogongrass stands in Java. They noted a "significant quantity" of dead, cured fuels that were created by and remained after burning, even in areas where cogongrass was green before the fire. They provide fuel loading and fire behavior estimates (based upon the BEHAVE fire behavior prediction system) for that community. Wibowo and others [162] provide fire behavior and severity information for a forest-mangrove/cogongrass community in West Java, Indonesia.

Fine fuels are the most important factor in ignition and spread of fire in Florida longleaf pine ecosystems [159], and cogongrass contributes a large fine fuel load. Observational [111] and anecdotal [110] accounts from Indonesia indicate that live cogongrass plants ignite and burn easily while still relatively green, and researchers in Indonesia note that cogongrass becomes very dry and flammable during the dry season [100]. Cogongrass's fuel properties and abundant litter may alter fire behavior on invaded sites in Florida [86,87]. Cogongrass is high in silica content, so the litter decays relatively slowly. In an Australian study, cogongrass had the slowest decay rate of 3 grass species studied. Its half-life rate of decay exceeded the study period of 24 weeks [59].

On Florida sandhill longleaf pine savannas, Lippincott [86,87] compared fine fuel loads, fire behavior, and fire effects on uninvaded and cogongrass-invaded sites. Cogongrass produced significantly more persistent, standing dead biomass compared to sites with native understory vegetation (P<0.05), resulting in a greater fuel load on invaded sites. Fire mortality of young longleaf pines was greater on cogongrass sites, and postfire fuel accumulations were also greater on cogongrass sites. Average fire temperatures were higher on cogongrass sites and reached a maximum of 856 °F (458 °C) compared to a maximum of 604 °F (318 °C) on uninvaded sites [86]. Such fires are severe enough to kill longleaf pine seedlings and saplings [71]. See the Fire Case Study for additional details.

Even in frequently burned communities, cogongrass may alter fire characteristics by increasing fine fuel loads. Platt and Gottschalk [113] investigated the effects of cogongrass and silkreed (Neyraudia reynaudiana), another nonnative tropical grass, on fine fuel loads in south Florida slash pine savanna in Everglades National Park. The historical fire regime of the area is surface fires at 5- to 10-year intervals. Fuels are almost all fine: woody debris is rarely present except after hurricanes. Firegrass (Andropogon cabanisii) and other bunchgrasses native to the area tend to produce greatest biomass the first year following a fire; they also mass flower at that time. Productivity of native bunchgrasses decreases with time since fire. In contrast, cogon grass produces prodigious biomass nearly every year. Study plots were on prescribed underburn rotations of 10 years or less. Study design compared plots with a native ground cover of firegrass with areas that contained 1 of the 2 nonnative grasses. Total plant biomass (measured as g/484 cm²) on plots with cogongrass was 1.7 times greater than on plots without cogongrass: a significant difference (P=0.03). Litter biomass was also significantly greater on plots with cogongrass (P=0.05) and was almost twice that on plots without cogongrass. Biomass of native plants was not different among plots with and without cogongrass [113]. 

Fire regimes: Little information is available on fire regimes where Brazilian satintail is native. Scott [128] investigated its occurrence in mixed muttonwood-copperleaf-Brazilian satintail-bracken fern savannas of montane eastern Peru. The study site was a tropical-humid forest area inhabited by Native Campa. He noted that the Campa practiced annual, dry-season burning around their village to maintain Brazilian satintail grassland. Areas where burning was abandoned succeeded to either bunchgrasses (in areas without sprouting woody species) or tropical forest. The origin of South American tropical savannas is unclear. Anthropogenic burning may be responsible. Hardpan soils over high water tables, wet climate, and a combination of anthropogenic burning, edaphic, and climatic factors are also suggested (numerous references cited in [128]). All researchers concede that regardless of their origins, South American savannas are currently maintained by frequent, intentional burning [128]. For information on postfire succession on Brazilian satintail old fields of Peru, see Successional Status.

No information is currently available on how Brazilian satintail affects fire intervals and behavior in southeastern pinelands. Information is needed on the fire ecology of Brazilian satintail in the United States and elsewhere.

Worldwide, cogon grass is favored by frequent surface fire in pine (Pinus spp.) and other savannas and by very frequent (<10-year rotation) stand-replacement fire in grasslands. In its native Southeast Asia, cogongrass occurs in systems that experience frequent fire including farmlands, grasslands, and the understories of tropical and subtropical forests, especially pine forests [42,97,141]. Charcoal evidence of fires in Borneo date back to the Holocene (review by [114]), but knowledge of natural fire regimes where cogongrass is native is lacking. In Indonesia [141] and Australia [160] cogongrass can tolerate annual fires, and frequent fire maintains cogongrasslands, which are successionally replaced by shrubs and/or secondary tropical forest in the absence of fire [100,141,144,161]. Cogongrass fuels fires that help maintain subtropical and tropical savannas and forest-grassland mosaics in Southeast Asia [144,161]. Forest fires can result in the spread of cogongrass in these ecosystems [161]. After large-scale fires in East Kalimantan in 1983 the area covered by cogongrassland expanded dramatically [46]. Small-scale fires within subtropical and tropical forest of Nepal maintain uneven-aged forest-grassland mosaics [108]. In subtropical Chir pine forests of Nepal and Pakistan, frequently burned slopes support cogongrass, several other grass species, and a variety of shrubs (Shrestha and Joshi 1997, cited in [120]).

Both fire and logging can increase establishment and spread of cogongrass, but this effect is "greatly enhanced" when these disturbances are combined [172]. Fires in Borneo and other tropical areas tend to occur during El Niño-induced droughts, and cogongrasslands expand during these drought-fire cycles [114,172]. Logged areas tend to be more susceptible to fire, and when it occurs, fire is more severe in logged areas. In Borneo, logged forests showed less understory diversity after fire compared to unlogged forest. Logged and burned forests were mostly dominated by cogongrass and/or Jack-in-the-bush, whereas these species were present but not dominant after fire in unlogged forests [172].

Shifting agriculture (slash-and-burn) has shortened fire intervals in many tropical areas to the point that warm-wet-climate pines and other overstory trees can no longer regenerate, creating large-acreage swards of cogongrassland where cogongrass had formerly occupied only small patches within forest mosaics [122]. Its spread in its native range in Southeast Asia is largely due to human clearing of tropical rain forests followed by frequent burning [38,46]. In northeastern India intervals between fires in Khasia pine forests have been shortened from 20- to 30-year intervals to 5-year intervals due to shifting agriculture. This has resulted in cogongrass dominance in fallow fields and cogongrass invasion into crops on cultivated lands [97]. Cogongrass is successionally replaced by woody species in the absence of further fire [172,174]. Slashing and burning every 4 to 6 years tends to exclude species other than cogongrass and other herbaceous weeds, while succession to woody species occurs with 10- to 20-year slash-and-burn cycles [127]. Repeated short-interval fires on cogongrasslands in Indonesia increase cogongrass abundance, reduce soil fertility, and increase soil erosion, ultimately making reversion to forest more difficult [51,52,53]. In Australia cogongrass has spread in tropical and subtropical regions where frequent burning occurs [13,115]. For example, it is an important component in an eucalyptus (Eucalyptus spp.) forests in northern Australia where Aborigines conduct frequent underburning [13].

Cogongrass in North America: There is potential for cogongrass to spread rapidly in warm-wet climate regions of the southeastern United States [90]. Cogongrass's rapid spread in peninsular Florida and edges of the northern Gulf of Mexico is thought to have increased fire hazard on invaded sites, and cogongrass populations are expected to continue to spread in the Gulf Coast region [4]. Cogongrass is well adapted to the subtropical pine ecosystems in that area (see Fire Adapations). Cogongrass may establish without or without fire [74,75], and can spread rapidly after fire [75,86,87].

Prior to the 20th Century, wildfires in the southeastern United States were most common in summer. Lightning strikes occur during the rainy season (May-October), with most lightning-ignited fires occurring in spring and summer [86,135]. Peninsular Florida's longleaf pine communities experienced frequent surface fires at 2- to 8-year intervals. These frequent fires maintained the savannas [24,101,123,140]. Southern Florida's slash pine forests probably had similar, but slightly longer (up to 15-year) intervals between surface fires. Reconstructing past fire regimes from fire scars has not been possible for southern Florida's pinelands [145]. Florida was inhabited by Aboriginals for thousands of years, and seasonality and extent of Aboriginal burning in the area is uncertain [135].

Fire behavior: Cogongrass invasion in pinelands of the southeastern United States may shorten fire-return intervals and increase fire severity over prehistoric conditions [16,86,87]. A report by the Mississippi Exotic Pest Plant Council identified cogongrass as 1 of the 4 most serious nonnative invasives in the Southeast, based, in part, upon its potential to alter natural fire regimes [90].

Cogongrass invasion may increase fire's rate of spread and intensity on invaded vs. uninvaded sites [86,87]. Compared to native bunchgrasses, cogongrass produces a more continuous bed of fine fuels that is highly flammable when dry. A study in southern Florida pine sandhills found that cogongrass fuelbeds were more evenly distributed than fuelbeds dominated by native grasses, resulting in more horizontally continuous burned areas [86]. On sites where cogongrass reaches maximum heights (see General Botanical Characteristics), it also increases vertical continuity of fuels, which may change the fire regime from surface to crown fire [16,87]. Observations in cogongrass sites in Mississippi indicated that flame heights were nearly twice those in sites dominated by wiregrass. Rates of fire spread were higher on cogongrass sites; however, maximum temperatures were lower (Grace, unpublished, cited by [50]). Ironically, cogongrass was once planted in firebreaks on the Withlacoochee State Forest, Florida [142].

The following table provides fire return intervals for plant communities and ecosystems where Brazilian satintail and cogongrass are important. For further information, see the FEIS review of the dominant species listed below. This list may not be inclusive for all plant communities in which Brazilian satintail and cogongrass occur. Find further fire regime information for the plant communities in which these species may occur by entering the species' names in the FEIS home page under "Find Fire Regimes".

FIRE EFFECTS

• IMMEDIATE FIRE EFFECT ON PLANT
• DISCUSSION AND QUALIFICATION OF FIRE EFFECT
• PLANT RESPONSE TO FIRE
• DISCUSSION AND QUALIFICATION OF PLANT RESPONSE
• FIRE MANAGEMENT CONSIDERATIONS

Fire top-kills cogongrass and consumes much of its associated litter [64,111,133].

Cogongrass sprouts from the rhizomes soon after fire [64,144]. Studies in Asia [49,97,136] and observations in Australia [160] show that burning increases cogongrass sprouting. A study in Java notes that cogongrass sprouted from "charred but obviously viable tillers" that "extended 4 to 6 inches (10-15 cm) above the soil surface" soon after fire. Forty days after fire cogongrass stem height averaged 4 feet (1.3 m) [111]. Several reviews indicate that fire and other disturbances stimulate flowering in cogongrass (e.g., [43,64,133]). Postfire mass flowering has been noted in cogongrass in Thailand (Paisooksantivantana, cited in [43]).

Cogongrass also establishes from wind-blown, off-site seed after fire [97,136]. Since it has a short-term seed bank [50], seedling establishment from soil-stored seed is possible.

Cogongrass is favored by frequent fires [64,144,160,172]. Garrity and others [46] stated the "real distinguishing factor for its persistence is the intermittent occurrence of fire." Coster [28] called fire "the greatest help" to cogongrass spread in Asia. Reviews state that cogongrasslands remain stable [64] and become dense monocultures [160] when burned annually.

Fire increases nutritional value of cogongrass in the short term. For 3 months after fire in central Florida, cogongrass on burned sites had significantly higher nitrogen and phosphorus content, and lower fiber content, compared to unburned cogongrass [86].

In postfire succession in tropical forest ecosystems, cogongrass is more abundant on previously logged sites, where it is initially important, then declines as woody plants establish and assume dominance (e.g., [103,144,161]). A severe drought in Indonesia in 1982 and 1983 caused widespread wildfires across Borneo [103,172]. Woods [172] compared early postfire succession on logged and unlogged sites after a fire in Borneo in April and May 1983. Canopy losses were higher and postfire seedling regeneration was dominated by cogongrass and hilo grass on sites logged <2 years before fire, and by cogongrass and Jack-in-the-bush on sites logged 6 years before fire. Grasses and lianas were present but not dominant and canopy losses were less severe on sites that were not logged prior to the fire [172]. Nykvist [103] found that grass biomass decreased with time on these sites, and mean grass biomass was 20 kg/ha at postfire year 5 and 3 kg/ha at postfire year 8.

Cogongrass can establish in both large and small gaps, growing best if gaps are created by fire [86]. On the Grand Bay National Wildlife Refuge, Mississippi, six 10 ± 10-m areas of longleaf pine savanna were burned under prescription on 6 April 1998. Cogongrass was transplanted onto transplant study plots 2 days after burning or seeded into seed study plots 3 days after burning. Percentage photosynthetically active radiation was 78% and 30% on burned and unburned plots, respectively. At postfire month 2, survivorship did not differ between cogongrass transplants on burned and unburned plots (P=0.72), but growth (mean shoot length) of transplants was greater on burned vs. unburned plots (P=0.0007). For seedlings, emergence did not differ between burned and unburned plots; however, survival of germinants at postfire months 1 and 2 was significantly greater on burned vs. unburned plots (P<0.05) [74].

Early in its postfire recovery, cogongrass may allocate most of its biomass to rhizomes. Following mowing and prescribed burning in an old field in India, cogongrass regenerated entirely from rhizome sprouts. At postfire year 1, aboveground:belowground biomass ratio of cogongrass was 1:4, which was the lowest ratio of the 4 plant species studied on burned plots [126].

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 cogongrass-infested sites and uninfested sites.

Cogongrass is extremely problematic for fire managers. It invades fire-adapted, warm-wet-climate ecosystems, reducing species diversity and ecosystem function. Cogongrass has the potential to shorten already short fire-return intervals to the point that native plant species cannot recover. Yet excluding fire from these fire-adapted ecosystems also results in loss of ecosystem diversity and function [29]. Rapid accumulation of dense cogon grass litter, along with its spreading rhizome mass, makes unassisted recruitment of native warm-climate plant species unlikely on infested sites [86,87].

Fire alone cannot control cogongrass; in fact, burning with no further treatments will promote it (see Plant Response to Fire). Burning can help control cogongrass when it is part of an integrated control plan, however [62,160]. By removing cogongrass top-growth, the rhizomes are forced to utilize stored carbohydrates to produce new growth, thereby weakening the rhizomes. Removing cogongrass litter and standing dead biomass prior to other treatment often improves the success of other control measures. For example, tillage is more effective, and herbicide application to growing tissues more precise, if biomass is first removed [70]. Johnson and Shilling [70] provide a contact list of managers and academics with experience using fire to control cogongrass.

Burning and allowing cogongrass regrowth, followed by tillage and herbicide treatment, is the most effective control measure for large, established infestations of cogon grass [35,133]. In a Florida study, burning was used to remove aboveground cogongrass biomass and prepare a bare soil study area on all plots. Postfire treatments were 2 herbicide sprayings, 2 diskings, or spraying/disking combinations. Imazapyr was applied 44 and 90 days after burning. Disking was done the day after burning and at postfire day 90. Measured 18 months after treatment, the most effective treatment was a 1st disking on postfire day 1, followed by spraying at postfire day 44, and a 2nd disking at postfire day 90. Compared to untreated plots, spraying alone provided 82% control, and disking alone provided 53% control. Disking followed by spraying without a 2nd disking resulted in 86% control [69].

After cogongrass suppression, establishment of native herbaceous species is needed for long-term control [170]. Shilling and others [133] stated "if a replacement species does not fill the niche occupied by cogongrass after suppression then cogongrass will simply refill the niche."

Studies in southeast Asia show that although slash-and-burn treatments reduce rhizome biomass, they also encourage sprouting and seedling establishment. Slashing alone may produce more sprouts than slashing and burning [124,136]. However, Woods [172] found that logging and burning in combination resulted in greater postfire establishment of cogongrass than either disturbance alone. A combination of prescribed burning and mowing reduced cogongrass in infested pastures in Australia. In heavily infested pastures, burning was followed by reseeding to pasture grasses, then mowed repeatedly [160]. A Malaysian manager reports that burning cogongrass early in the dry season reduces next-year fuel loads, while late dry-season fires tend to increase next-year fuel loads [121].

FIRE CASE STUDIES

• FIRE CASE STUDY CITATION
• SPECIES INCLUDED IN THE SUMMARY
• FIRE CASE STUDY REFERENCES
• STUDY LOCATION
• SITE DESCRIPTION
• PREFIRE PLANT COMMUNITY
• PLANT PHENOLOGY
• SEASON/SEVERITY CLASSIFICATION
• FIRE DESCRIPTION
• FIRE EFFECTS ON PLANT COMMUNITY
• FIRE MANAGEMENT IMPLICATIONS

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. [86].

Lippincott, Carol L. 1997. Ecological consequences of Imperata cylindrica (cogongrass) invasion in Florida sandhill. Gainesville, FL: University of Florida. 165 p. Dissertation. [87].

Groundlayer vegetation differed on invaded and uninvaded plots. The ground layer on invaded sites was mostly nonnative cogongrass (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 [86].

Cogongrass was intentionally introduced into the Brooksville area in the early 1990s as a forage crop [143]. It was probably introduced in the Citrus Tract from seed-contaminated road fill (Blanchard, cited in [87]). During the study period, cogongrass occurred in scattered swards in the Citrus Tract. Cogongrass patch size ranged from a few square meters to several hectares [87].

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, 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 [87].

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 [86].

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 [87]. 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 cogongrass (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 [87]:

Prefire fine fuel load was significantly less on native sandhill sites compared to cogongrass sites (P=0.04). From 0 to 0.49 m in height, fine fuel mass did not differ between uninvaded and cogongrass-invaded sites; however, fine mass of fine fuels from 0.50 to 1.50 m was higher (P<0.01) on cogongrass sites [86]. Prefire fuel loads at 3 heights were [87]:

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 cogongrass (260.9 ± 13.7 °C) and native sandhill (218.3 ± 14.5 °C) sites [86]. Fuel load ratios and fire temperatures by height were [87]:

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) [87]:

Fire mortality of longleaf pine juveniles was higher on cogongrass-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 [86,87]:

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 [87]. Poor growth in small longleaf pine juveniles was probably due to competitive interference by cogongrass, rather than direct fire effects to small longleaf pines [86]. (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 plots (P=0.86). For all size classes, stem diameter growth of longleaf pine juveniles was not significantly different on invaded and uninvaded plots [87].

Although cogongrass increases fire mortality of longleaf pine seedlings, mature longleaf pines may not be directly affected by cogongrass presence. In this study, growth of longleaf pines greater than 10.4 cm dbh was not slowed by cogongrass [86].

Cogongrass-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 ± 297 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 cogongrass reached a maximum of 458 °C on some strips at all aboveground heights measured. After fire, fine fuels accumulated more quickly on invaded plots [86,87].

These mortality data and instantaneous maximum temperature measurements at given points suggest that longleaf pine juveniles may succumb to cogongrass-fueled fires [87]. Additional data on fire duration (e.g., Jacoby and others [68]) will help determine direct fire effects of cogongrass 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 cogongrass sites, which have more fuels and higher fire temperatures compared to sites with native bunchgrass fuels [87]. Koskela and others [78] had similar findings in a Sumatran pine (Pinus merkusii)/cogongrass land 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 cogongrass [78].

MANAGEMENT CONSIDERATIONS

• IMPORTANCE TO LIVESTOCK AND WILDLIFE
• OTHER USES
• IMPACTS AND CONTROL

Cogongrass is generally detrimental in wildlands and pastures in North America. It reduces habitat quality for wildlife that have evolved in pine/bunchgrass ecosystems [43,86]. It is little used as forage in the United States even though it was originally planted for that purpose. Pendleton [110] warned against cogongrass introduction in 1948:

Cogongrass "is anything but nutritious. Certainly its hazard as a potential weed for upland crops in the tropical and subtropical portions of the western hemisphere is a very much more serious threat to agriculture than the small amount of benefit it can possibly be as a forage. The writer feels very strongly that steps should be taken at once to completely eradicate this noxious weed from the western hemisphere" [110] (italics are Pendleton's).

Although cogongrass is weedy in wildlands where it is nonnative and in agricultural systems worldwide, it has a valuable ecological role as fuel and forage in grasslands where it is native. In Royal Bardia National Park, Nepal, for example, cured cogongrass helps fuel the natural fire cycle that maintains tropical forest-grassland mosaics. Live cogongrass provides cover for ground-nesting birds and forage for grazing animals. Cogongrass is an important component of the food web for threatened [152] animals in the Park including hispid hares, swamp deer, and tigers [108]. In Borneo, the Banjarese historically burned open fields with cogongrass to create deer habitat and forage [114]. Asian and African ranchers use cogongrass as cattle forage [30,35]. Cogongrass is expected to become less important forage in developing countries as it is replaced by plantings of more nutritious grass species [64].

Palatability: Cogongrass is relatively unpalatable and unnutritious for livestock and North American wildlife [40,41,43,58,86]. It is lower in nitrogen and higher in fiber and silica compared to native wiregrasses (Aristida spp.) of the Southeast [24,26,86]. The leaf blades are sharp and rough at the edges, discouraging animals from grazing [26]. New spring growth and postfire sprouts are palatable to livestock for 3 to 4 weeks; however, plants become coarse and fibrous after that [160]. In a rangeland study in subtropical Australia, cogongrass cover increased in response to cattle grazing at the expense of common carpet grass (Axonopus fissifolius), which is more palatable and nutritious [60]. Stober [139] described cogongrass as unpalatable to domestic sheep in Malaysia; however, domestic sheep can learn to graze cogongrass [156].

As it becomes more common in the Southeast, cogongrass will affect grazing wildlife. Gopher tortoises, a federally threatened species [152], prefer native grasses and forbs to cogongrass [86]. Three North American skipper butterflies graze cogongrass in the caterpillar stage [17].

Nutritional value: Nutritional studies of cogongrass in the Southeast are few. Lippencott [86] found that compared to native Florida sandhill herbs, cogongrass was higher in nitrogen and phosphorus and lower in fiber for the first 3 months after fire. By 6 postfire months, cogongrass provided less nitrogen and phosphorus, and by postfire month 14, it was higher in fiber compared to native herbs. Studies conducted on cogongrass in Asia are reported below.

Most sources claim that cogongrass forage quality declines quickly, is low in minerals (particularly phosphorus), and that cattle require nutritional supplements when grazing cogongrass ([19] and references therein, but see [40] for a contrasting viewpoint). In India, domestic goats on a native grassland mixture that included cogongrass showed poor weight gain [175]. Asian ranchers have successfully raised cattle on cogon grass-legume pastures [19]. Nutritional content of cogongrass from Asian sources (country not reported) was [73]:

Analysis of cogongrass in Malaysia showed (as cited in [64]):

A Thailand study suggests fire and repeated grazing reduce forage quality of cogongrass. A cogongrass sward was burned on 23 March 1978, then harvested every 3 weeks from April through October 1978. Mean dry-matter nitrogen content was 2.93% in April, declining to 0.56% in October. Phosphorus content declined from 0.90% to 0.37%, and in-vitro digestibility declined from 71% to 39% in the same time period. Nutrient values on an undisturbed 5-year-old cogongrass sward were generally lower: 0.66% nitrogen, 0.12% phosphorus, and 31.4% in-vitro digestibility [40].

Cover value: Cogongrass stands are poor habitat for most southeastern wildlife species [43]. Cogongrass is about 3 times the height of native Florida grasses. Its height probably impedes movement of small animals. Ground-dwelling species can be displaced by cogongrass's dense cover [70]. In central Florida, habitat quality of 2 keystone fossorial animals, gopher tortoises and scarab beetles, was reduced on cogongrass-invaded sites compared to uninvaded sites. Beetle populations were reduced approximately 76% on invaded sites. Threatened [152] gopher tortoise populations were too low to allow quantitative assessment; however, thick rhizome growth that deters burrowing, reduces the number of open areas for egg laying, and reduces herbaceous forage species, lowers gopher tortoise habitat quality. Southeastern pocket gophers, another keystone fossorial animal, were not affected by cogongrass presence [86].

In traditional Asian folk medicine, cogongrass is used as a tonic, an emollient, an anti-inflammitory, and a fever-reducing agent (references in reviews by [48,90,91,92]). Chemical and pharmacological studies are underway to assess potential uses of cogongrass in modern medicine [90,91,92,112]. A cogongrass extract shows anti-insecticide properties against mosquitoes [99].

'Red Baron,' a cultivar of cogongrass with red leaves, is commercially available and planted as an ornamental despite cogongrass's federal and state listings as a noxious weed [27,171] an laws against its use [149]. 'Red Baron' is usually described as infertile and nonspreading, but data are lacking to support the claim [26]. Greenhouse studies suggest 'Red Baron' is at least capable of vegetative spread. After 3 months in the greenhouse, 'Red Baron' rhizomes produced a similar number of secondary rhizomes compared to Brazilian satintail rhizomes (x=5.7 and 5.1 rhizomes for 'Red Baron' and Brazilian satintail, respectively), and significantly more secondary rhizomes than Imperata cylindrica var. major, the "wild type" cogongrass (x=3.9 I. c. var. m. secondary rhizomes, p=0.05). Growth rates of the 2 cogongrass types and Brazilian satintail were similar [133]. 'Red Baron' may be more shade tolerant than the wild type [27], and individual 'Red Baron' rhizomes may grow "aggressively" [9]. Use of 'Red Baron' is not recommended in the United States for ecological reasons [147].

Cogongrass is identified as a large potential hazard to remnant old-growth longleaf pine stands due to its ability to invade undisturbed old-growth forests of the Southeast [155]. In central Florida, Lippencott [86] found cover and diversity of native herbs, shrubs, palms, and small longleaf pines and oaks (Quercus incana, Q. laevis, Q. geminata) were significantly reduced on cogongrass sites compared to uninfested sites (P< 0.01) (see The Fire Case Study Imperata cylindrica in a Florida sandhill longleaf pine community. Yager [176] is conducting research on cogongrass rate of invasion into longleaf pine/bluestem and longleaf pine/shrublands in Mississippi. Preliminary data show an expansion rate ranging from 0 to 1.6 feet (0.5 m) over a 6-month period (April-Oct. 2002). Expansion rate is not significantly different between habitats [176]. Spread of cogongrass outside the lower Coastal Plains states is unlikely because of cogongrass's poor tolerance to low temperatures [106,165].

Cogongrass allelopathy has been implicated in laboratory experiments [20,26,65,76,77,117]; however, such claims are based upon research using cogongrass extracts at concentrations that do not occur under field conditions. Reputed allelopathy of cogongrass awaits reciprocal transplant experiments in the field and/or greenhouse.

Silvicultural: Cogongrass competes with hardwood species for light, water, and nutrients. Cogongrass grows so tall and thick that it decreases growth and increases mortality of young trees [90]. Allen and others [4] describe cogon grass as particularly problematic in peninsular Florida pinewoods. Lippencott's [86] Florida study suggests that pine and oak regeneration is reduced in cogongrass swards; however, she found that median basal area of mature pines was greater on cogongrass sites compared to uninfested sites. Basal area of oaks did not differ between sites (P<0.01). She postulated that mature longleaf pine was unaffected by understory cogongrass cover once longleaf pine reached a critical size (10.4 cm dbh or 85.1 cm² basal area in her study), but that longleaf pine regeneration would not occur until cogongrass was controlled [86].

Because cogongrass increases fire severity, wildfires in pine plantations infested with cogongrass may kill pine seedlings that are normally fire resistant [90].

Tropical ecosystems: Cogongrass is invasive in tropical and subtropical regions worldwide. Cogongrass is a troublesome agricultural weed in Asia and Africa [2,6,10,21,22]. Repeated agricultural burning has converted millions of acres of tropical forest to cogongrasslands [15]. In a 1997 survey, Garrity and others [46] estimated that about 35 million acres (14 million ha) were dominated by cogongrass in Asia, mostly as a result of frequent fire on shifting agricultural lands. In Indonesia, for example, shifting agriculture has resulted in a type conversion of tropical forest to coarse tropical grasslands dominated by cogongrass and/or wild sugarcane (Saccharum spontaneum) [42,100]. Cogongrass coverage increased in Indonesia from 31.3 million acres (12.5 million ha) in 1996-1997 to 58 million acres (23.2 million ha) in 2000. Cogongrass coverage also increased in tropical forest understories [100]. Van der Wall [154] demonstrated that it takes about 4 or 5 slash-and-burn cycles to effect a type conversion from tropical forest to cogongrassland.

Control: Cogongrass is not easy to kill. Its extensive rhizome system requires several treatments before control is effective [43,133]. Long-term control of cogongrass only works if the cogongrass monoculture is changed to a competitive, diverse plant community [43]. Postcontrol revegetation needs to be accomplished quickly in order for a stable plant community to establish. Posttreatment inventory and spot-control treatments are needed to control new cogongrass infestations [70].

Prevention: The most efficient and effective method of managing invasive species is to prevent their invasion and spread [131]. Preventing the establishment of nonnative invasive plants in wildlands is achieved by maintaining native communities and conducting aggressive surveying, monitoring, and any needed control measures several times each year. Preventing the introduction of cogongrass into uninfested areas, and early control of small infestations, should be a priority [70]. Monitoring efforts are best concentrated on the most likely sites of cogongrass invasion: disturbed soil, roadsides, old fields, pine savannas, and burns. Uninvaded sites should be periodically surveyed to detect new invasions. The Center for Invasive Plant Management provides an online guide to noxious weed prevention practices.

Limiting seed and rhizome dispersal reduces chances for cogongrass spread. Regular cleaning of road equipment, and restrictions on long-range movement of equipment, can limit cogongrass spread. Removal of 'Red Baron' cultivars from the market may also reduce cogongrass spread [90].

Integrated management including burning, mowing, tillage, chemical, and/or cultural control will increase the likelihood of cogongrass control [35,69,133,166]. Successful control in Florida employs a combination of mechanical, chemical, and/or burning treatments. Johnson and Shilling [70] recommend beginning an integrated control program in late spring or summer, when cogongrass growth is peaking. Some treatments, like mowing and spot herbicide spraying, should be implemented year-round [70].

Physical/mechanical: Cogongrass can be controlled by mowing, disking, pressing, or a combination of these methods [146]. Cogongrass is difficult to remove by hand cultivation due to its rhizomatous habit [116]. Mechanical treatments may not be possible or practical on some wildland sites.

Mowing treatments alone cannot control cogongrass. In the Philippines, Sajise [124] found cutting treatments increased cogongrass sprouting compared to uncut control plots. Plants cut every 2 months produced more sprouts compared to plants cut monthly [124]. Frequent, repeated mowing treatments, or mowing followed by reseeding and further mowing treatments, can reduce cogongrass [166]. An Australian review recommends remowing before cogongrass flowers or reaches 12 inches (30 cm) in height [160].

Disking, or a combination of disking and other treatments, helps control cogongrass. Testing 11 populations in northern and central Florida, Shilling and others [133] found disking alone provided short-term control of cogongrass; however, disking and imazapyr application provided 96% control of cogongrass 1 year after treatments. Mowing in late spring to remove old growth and thatch, followed by disking 6 to 8 weeks later, when plants are 6 to 12 inches (20-30 cm) tall, was also effective [133]. Plants should be disked before they reach 30 inches (75 cm) in height. A second disking is needed 2 to 3 weeks later if disking is the only control method used [116].

Another northern Florida study illustrates the importance of multiple treatments. One year after mechanical or mechanical/chemical treatments, 1 summer mowing and disking treatment had increased cogongrass density; 2 mowing and disking treatments provided "moderate" control; summer mowing and disking, fall imazapyr or glyphosate treatment, and a 2nd summer mowing and disking provided 100% control  [170]. In an Alabama study, Wilcut and others [165] found tilling cogongrass rhizomes to depths of  2 to 3 inches (5-8 cm) greatly reduced cogongrass sprouts. Rhizomes exposed to 23 °F to 25 °F (-5 °C to -4 °C) temperatures for 24 hours were also killed, suggesting that cold-weather tillage can maximize rhizome kill.

Small-farm operations in Asia commonly press or drum roll cogongrass stands, which breaks and lodges stems and leaves. In Indonesia, mechanical lodging is more effective than fire, mowing, or disking measures because cogongrass rhizomes are forced to grow through their own, artificially compacted, dense litter. Legume species tend to be better competitors for light after compaction treatments [116] (see Cultural control). Using roller/compactors, mechanical lodging may be effective as a part of an integrated control program on some sites.

Fire: See Fire Management Considerations.

Biological: There are no biological control agents currently approved for cogongrass control [116,134,148]. Cogongrass has several insects and fungal pathogens that infest it in Asia [36]. Two fungal pathogens (Bipolaria sacchari and Drechslera gigantea) have shown potential as cogongrass control agents in greenhouse trials [177,178].

Cogongrass is widely used as livestock forage in Asia and Africa [40,41]. Domestic sheep grazing has been successfully used as a control measure in Malaysia [156]; however, there are no studies on using livestock to help control Brazilian satintail or cogongrass in the United States. Some ranchers in the Southeast use cogongrass swards as winter cattle range [143]. Cattle weight gain is not as good on cogongrass compared to pasture grasses [40,41], but livestock grazing may be a useful part of an integrated Brazilian satintail/cogongrass control program if the primary management objective is weed control and not meat or milk production. Studies on how livestock use affects Brazilian satintail and cogongrass cover and reproduction are needed.

Chemical: Herbicides may provide initial control of a new invasion or a severe infestation, but used alone, they are rarely a complete or long-term solution to invasive species management [18]. Herbicides are most effective on large infestations when incorporated into long-term management plans that include replacement of weeds with desirable species, careful land use management, and prevention of new infestations. Control with herbicides is temporary, as it does not change the conditions that allowed the invasion to occur (e.g. [179]). See The Nature Conservancy's Weed Control Methods Handbook for considerations on the use of herbicides in Natural Areas and detailed information on specific chemicals.

Imazapyr and glyphosate help control cogongrass [43,70,146,148,165,167]. Imazapyr is nonselective and has some soil residual activity. Glyphosate is also nonselective but is less residual, offering more flexibility in timing and species selection for posttreatment revegetation [44]. Rhizomes must be killed for effective, long-lasting control [70,88,96]. Depending upon rhizome reserves, multiple herbicide applications and follow-up spot treatments are usually needed for complete rhizome kill and long-term control [26,96]. Fall applications are usually recommended because cogongrass transports carbohydrates and herbicides down into its rhizomes and roots at that time of year [70,88,96]. Shilling and others [133] found autumn applications of glyphosate or imazapyr provided better control than spring or summer applications. Winter applications can be effective if plants are still green. Analysis of rhizome total nonstructural carbohydrates (TNC) can show when carbohydrate allocation is directed toward  rhizomes and therefore, when herbicide applications are likely to be most effective. In Florida, TNC content showed a small peak in December and January, and showed greatest gains in February and May. Rhizome TNC content was lowest in November [133]. Twelve and sixteen months after Florida field trials, Gaffney [44] found December application was twice as effective as either September or January application. Imazapyr gave better control than glyphosate.

Follow-up herbicide applications in spring, prior to flowering, can suppress cogongrass seed production [96]. Young plants can often be controlled using fewer applications and/or lower doses of herbicide than plants with well-developed rhizomes [35]. Demers and Long [31] provide standard application rate recommendations for cogongrass. High concentrations of herbicides do not necessarily translate into higher rate of cogongrass kill compared to recommended rates of application. In a loblolly pine plantation study in Florida, Ramsey and others [118] report high rates of glyphosate or imazapyr actually inhibit translocation of the herbicide to rhizomes. They recommend half-dose applications, sprayed twice a year, to ensure good rhizome kill. Terry and others [146] found glyphosate application to newly burned cogongrasslands was not effective. Glyphosate is usually a foliar-applied and foliar-absorbed herbicide, and top-killed cogongrass lacked sufficient aboveground surface area to carry the herbicide  to rhizomes [146].

Carefully timed herbicide treatments may control cogongrass for as long as 1 or 2 years, but without establishment of desirable native species, cogongrass can eventually reinfest treated areas [118,133] (see Cultural control below).

Altering soil nutrient status can increase the competitive ability of native species on sites with cogongrass. In a Mississippi study, addition of large amounts of phosphorus slowed rate of cogongrass invasion into longleaf pine savannas. Native plant species were seemingly not affected by the fertilizer. The mechanism of cogongrass inhibition was unknown, but the authors speculated that the addition of phosphorus could have caused changes to the soil microbial community, chemical changes in the soil, or a phosphorus toxicity reaction in cogongrass [14]. Cogongrass forms mycorrhizal associations in Indonesia (Tjitrosemito and others 1994, as cited in [146] ); these associations help cogongrass obtain phosphorus, which is often limiting in tropical ecosystems. This competitive advantage is lost, however, where phosphorus is not limiting. Applying phosphorus on sites where it is already plentiful may help control cogongrass [146].

On a phosphate mine site in central Florida, nonnative hairy indigo (Indigo hirsuta), nonnative perennial ryegrass (Lolium perenne), native bahia grass (Paspalum notatum), native switch grass (Panicum virgatum), or native partridge pea (Chamaecrista fasciculata) were planted after imazapyr or glyphosate treatments to control cogongrass. Imazapyr treatment followed by hairy indigo seedings gave best cogongrass control (100% control at posttreatment year 1), followed by imazapyr and switch grass or partridge pea plantings (86% control). Perennial ryegrass and bahia grass showed poor establishment [133]. Shilling and others [133] found a significantly lower (p<0.001) density of cogongrass establishment in fields planted to bahia grass. Presence of bahia grass lowered cogongrass seedling density by 25% and lowered cogongrass ramet density by 37%. A combination of herbicides and revegetating with Bermuda grass and hairy indigo also gave good control of cogongrass 2 years after posttreatment seedings [133].

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