Sporobolus compositus



INTRODUCTORY


Photo © John Hilty, www.illinoiswildflowers.info/

AUTHORSHIP AND CITATION:
Meyer, Rachelle. 2010. Sporobolus compositus. In: Fire Effects Information System, [Online]. U.S. Department of Agriculture, Forest Service, Rocky Mountain Research Station, Fire Sciences Laboratory (Producer). Available: http://www.fs.fed.us/database/feis/ [].

FEIS ABBREVIATION:
SPOCOM

NRCS PLANT CODE [235]:
SPCOC2

COMMON NAMES:
tall dropseed
composite dropseed
Drummond's dropseed
Mississippi dropseed
head-like dropseed
meadow dropseed
rough dropseed

TAXONOMY:
The scientific name of tall dropseed is Sporobolus compositus (Poir.) Merr. (Poaceae). Three varieties of this species are recognized [11,123,235]. In the few instances in which unambiguous information regarding variety is available, this review refers to varieties by the following common names:

Sporobolus compositus var. clandestinus is not included in this review because it is considered a separate species, S. clandestinus (Biehler) A.S. Hitchc. [11,123,147,235].

SYNONYMS:
Sporobolus asper (Michx.) Kunth [45,56,57,104]
Sporobolus asper (Beauv.) Kunth [123]
Sporobolus pilosus Vasey [94,103]
Sporobolus drummondii Vasey
Sporobolus aspera (Michx.) Kunth
Sporobolus attenuatus Nash [103]

LIFE FORM:
Graminoid


DISTRIBUTION AND OCCURRENCE

SPECIES: Sporobolus compositus

GENERAL DISTRIBUTION:
Tall dropseed occurs in all states except California, Nevada, Florida, South Carolina, New Hampshire, Alaska, and Hawaii [45,94,104,123,235,258]. However, it is most widespread in the Great Plains and the Midwest. It is common from Ohio and Indiana west through Illinois, Missouri, and Iowa to North Dakota [218] and South Dakota [55], south through Nebraska, Kansas, and Oklahoma to Texas. It is scattered in the southeastern [11,103] and northeastern [65,147,184,200,241] United States. It is even more patchily distributed in the western United States, including Utah [211], Colorado [251], Wyoming [57], and Montana [56]. Plants Database provides a distributional map of tall dropseed.

Composite dropseed is the most widespread of the 3 varieties, occurring throughout the species' range [11,65,103,235]. Drummond's dropseed may be most common in Texas [11,53,187] but has been reported in several states including Louisiana, Mississippi, Alabama, Missouri [187,235], Oklahoma, Kansas [11,235], Iowa, Kentucky, Tennessee, and Georgia [235]. According to Engstrom [65], a reported occurrence of tall dropseed in Maine [184] was actually Drummond's dropseed, although this is well outside its typically described range. Mississippi dropseed apparently has the most restricted distribution [187,235], with reports limited to Texas [53,167,187], Louisana, and specific areas in southwestern Arkansas, southern Mississippi [187,235], and southeastern Missouri [235]. It may occur in other areas of the south-central United States [11,235].

HABITAT TYPES AND PLANT COMMUNITIES:
The following information is based primarily on floras, habitat classifications, primary literature, a BLM review of fire use in the Great Plains [237], and a New England conservation and research plan for composite dropseed that includes a review of its biology and ecology [65].

Tall dropseed occurs in tallgrass [65,70,80,172,223] and mixed-grass [65,122,185,203,223,237] prairies, savanna communities [27,35,60,79,118,133,172], and disturbed areas [11,18,53,94,106,116,147].

Tall dropseed is a common component of tallgrass prairie throughout the Great Plains [65,70,80,150,159,172,179,223,255]. Graminoids in tallgrass prairies with tall dropseed include little bluestem (Schizachyrium scoparium) [50,70,79,106,132,159,201,208,230], big bluestem (Andropogon gerardii) [50,70,79,102,106,140,150,159,201,208], indiangrass (Sorghastrum nutans) [50,70,79,108,150,159,208,230], sideoats grama (Bouteloua curtipendula) [106,132,140,159,201,208], and switchgrasss (Panicum virgatum) [50,70,150,159,208,230]. In North Dakota, tall dropseed was a frequently occurring species in bluegrass-bluestem-needlegrass (Poa-Andropogon-Stipa) upland tallgrass prairie and infrequent in saltgrass-barley-bluegrass (Distichlis-Hordeum-Poa) lowland tallgrass prairie [95]. Tall dropseed occurs in Gulf coast prairies [49,58,161,162,167,172,207,230]. Species which often occur in these communities include little bluestem, brownseed paspalum (Paspalum plicatulum) [49,50,172,230], indiangrass [49,50,172], switchgrass and eastern gamagrass (Tripsacum dactyloides) [49,172,230]. Based on 63 sites from North Dakota to Texas, tall dropseed was negatively correlated with porcupine grass (Hesperostipa spartea) and prairie dropseed (Sporobolus heterolepis) and positively correlated with indiangrass (P<0.0001) [51].

Tall dropseed frequently occurs in mixed-grass communities. It occurs in mixed-grass or midgrass prairies in Oklahoma [122], Kansas [65,125,135,146,205], South Dakota [205], and North Dakota [185]. Western wheatgrass (Pascopyrum smithii) [65,111,146,205], big bluestem [65,146,205], and sideoats grama [5,65,111,205] are common associates in these communities. Other species include buffalograss (Buchloe dactyloides), blue grama (Bouteloua gracilis) [108,111,205], Canada wildrye (Elymus canadensis) [146], and mat muhly (Muhlenbergia richardsonis) [185]. Tall dropseed occurs in southwestern Kansas rangelands with little bluestem, sideoats grama, big bluestem, western wheatgrass, buffalograss, blue grama, saltgrass (Distichlis spicata), fourwing saltbush (Atriplex canescens), broom snakeweed (Gutierrezia sarothrea), and common pricklypear (Opuntia monacantha) [71]. Although rare, tall dropseed has been reported in shortgrass prairie communities [3,111,122].

Tall dropseed is often associated with similar species in prairies outside of the Great Plains. For instance, tall dropseed occurs with big bluestem in Ontario [33], New England [65], Illinois [173], south-central Kentucky [245], and prairie openings in the Mississippi gulf coastal plain [253]. Tall dropseed occurs with little bluestem and indiangrass in New England [65], Ohio [93], Illinois [16,173], south-central Kentucky [245], and the Mississippi gulf coastal plain. In prairie openings of the upper coastal plain of Mississippi tall dropseed also occurs with switchgrass [163,253] and eastern gamagrass [163]. An Alabama prairie site was described as similar to Texas prairies and included silver bluestem (Bothriochloa saccharoides) and tall dropseed [244]. Tall dropseed occurred on a mat muhly-dominated site in Maine [184]. Grassy meadows of southeastern Ohio are an example of communities with tall dropseed that are not typical Great Pains grasslands. These communities are comprised of several graminoids and forbs including orchardgrass (Dactylis glomerata), poverty rush (Juncus tenuis), bentgrasses (Agrostis spp.), sedges (Carex spp.), plantains (Plantago spp.), and clovers (Trifolium spp.) [206]. Although tall dropseed has been noted on beaches in the northeast [65,187], as of late 2009, associated species in these areas have not been reported.

Tall dropseed occupies savannas with honey mesquite (Prosopis glandulosa), oaks (Quercus), junipers (Juniperus), or pines (Pinus) and openings within woodlands and forests comprised of these and other woody species. In Texas, tall dropseed occurs in mesquite/mixed-grass communities [9,27,60,169,228]. It may be most common in bottomland areas of these communities [59]. Oak species in savannas with tall dropseed include post oak (Quercus stellata), blackjack oak (Q. marilandica) [35,79,118,133,172,208], live oak (Q. virginiana), Texas red oak (Q. texana) [35,236,237], and Texas live oak (Q. fusiformis) [155,225]. Tall dropseed occurs in post oak-blackjack oak savannas or woodlands in southern Illinois [62], Kansas [133,172], Oklahoma [79,133,172], Arkansas [118], and Texas [35,60,133,172,208,209]. In the Ozarks, tall dropseed occurred infrequently in glades within a post oak-black hickory (Carya texana) forest of Missouri [131] and was listed as a characteristic species on 2 plots codominated by blackjack oak and black hickory in Arkansas. Tall dropseed also occurred on a plot within a savanna-glade-woodland mosaic of the Arkansas Ozarks dominated by white oak (Q. alba) and southern red oak (Q. falcata) [118]. In Kansas, tall dropseed occurred in cross timbers vegetation [135] comprised of post oak and blackjack oak [134], and in cedar hill prairie comprised of "low needle-leaf evergreen trees" [135], likely a juniper (Juniperus spp.) species. Tall dropseed has been reported in glades within juniper-dominated or codominated communities comprised of Ashe juniper (J. ashei) [35,237], Ashe juniper and oaks (Quercus spp.) [256], and Pinchot's juniper (J. pinchotii) [143,217] in Texas; and eastern redcedar (J. virginiana) in Ontario [36], Oklahoma [107], and Kentucky. On the site in Kentucky, tall dropseed occurred in openings of a woodland comprised of eastern redcedar, blackjack oak, chinquapin oak (Q. muehlenbergii), and Carolina buckthorn (Frangula caroliniana) [43]. It was considered a characteristic species of the chinquapin oak-eastern redcedar/little bluestem-false aloe (Manfreda virginica) wooded herbaceous association in the Stones River National Battlefield in Tennessee [165]. Tall dropseed has been reported in xeric Tennessee glades being invaded by several woody species including junipers and pines [48]. Tall dropseed occurred on an experimental site in Mississippi in a longleaf pine (Pinus palustris) woodland [242]. A flora notes tall dropseed's occurrence in pine woodlands and live oak-pine forests [11]. Grass species commonly occurring with tall dropseed in forest and woodland openings include buffalograss [9,60,143,169,256], little bluestem [35,43,48,79,107,256], sideoats grama [35,36,48,256], and Texas wintergrass (Nassella leucotricha) [35,143,256]. Mississippi dropseed may be most common in woodlands [53,187] and the edges of wooded areas [53].

Tall dropseed is often associated with disturbed sites [53,65,94,147], such as old fields [18,79,106,107,201,254], roadsides [11,26,65,94,147], and railroad rights-of-way [11,65]. Species cooccurring with tall dropseed in these areas include prairie threeawn (Aristida oligantha) [107,190,201], arrowfeather threeawn (Aristida purpurascens) [79,106], ragweeds (Ambrosia spp.), and lespedezas (Lespedeza spp.) [79,106,107]. Tall dropseed is commonly reported with western ragweed (A. psilostachya) [143,169,238] and annual broomweed (Amphiachyris dracunculoides) [143,238] in grazed prairies and savannas. Sumac (Rhus spp.) [106,107,143] cooccurs with tall dropseed in some disturbed areas such as grazed communities and old fields. In Minnesota [18,254] and Iowa [26], tall dropseed occurred with Kentucky bluegrass (Poa pratensis) on disturbed sites. In New Mexico, tall dropseed occurred on an abandoned mine site that had been experimentally planted with oneseed juniper (Juniperus monosperma) [72].

Vegetation classifications describing plant communities in which tall dropseed is dominant are listed below:

Great Plains

Nebraska

Texas Blackland Prairie


BOTANICAL AND ECOLOGICAL CHARACTERISTICS

SPECIES: Sporobolus compositus
GENERAL BOTANICAL CHARACTERISTICS:
Botanical description: This description covers characteristics that may be relevant to fire ecology and is not meant for identification. Keys for identification are available (e.g., [11,45,53,94,104]).

Tall dropseed is a mid-sized [65,227], tufted [45,65,104], warm-season [166,205,227], perennial grass [11,45,94,105]. Tufts can contain substantial amounts of remnant plant material [45]. On a "prairie reconstruction" site at a Kansas museum, tall dropseed grew to an average basal diameter of 3.9 inches (10 cm) in the first year [178]. Culms are generally solid [45,65,94,105] and range from 8 to 51 inches (20-130 cm) tall [11,45,94,105]. Tall dropseed leaves are generally from 2 to 28 inches (5-70 cm) long [11,94], 1 to 4.5 mm wide [11,45,65,94,105], and range from flat to involute [11,45,94]. The 1-flowered spikelets [55,65,166,224] are typically 3 to 6 mm long [11,55,104,241] and are arranged in a panicle. The panicle is typically greater than 1 inch (3 cm) long [11,94,104] and can reach 12 inches (30 cm) or more [11,45,65]. Two to 6 panicles per flowering culm [65] are partially to wholly included in the upper sheath [11,65,94,166,224,241,251]. The 1 to 2 mm fruits are laterally flattened ellipsoids. Pericarps are gelatinous and slip from the seed when wet [11]. Several floras [11,53,94,103] and a thesis [187] provide characteristics of specific varieties.

Composite dropseed and Drummond's dropseed do not have rhizomes, while Mississippi dropseed has scaly creeping rhizomes [11,53,65] that are slender and may produce 1 or 2 culms [187].

Although a typical range of tall dropseed root depths is not described in the available literature, tall dropseed roots may extend to at least 18 inches (45 cm) deep. Tall dropseed root biomass at depths of 8 to 18 inches (20-45 cm) averaged over 230 g/m² following 2 years of growth in experimental plots in the Blackland Prairie of central Texas [255]. The majority of roots in an Oklahoma tallgrass prairie where tall dropseed was an important component occurred in the 0- to 20-inch (0-50 cm) zone of the soil [205].

In a study tracking the survival of perennials on plots in livestock enclosures near Hayes, Kansas, from 1932 to 1972, the maximum observed lifespan of a tall dropseed individual was 26 years [140].

Tall dropseed growth may be enhanced by mycorrhizae. Small but significant (P<0.05) increases in tall dropseed were observed on sites where dominant grasses were removed and mycorrhizae were not suppressed, compared to the treatment where dominant grasses were removed and mycorrhizae were suppressed [210].

Raunkiaer [183] life form:
Hemicryptophyte [17]
Geophyte (Mississippi dropseed, see above)

SEASONAL DEVELOPMENT:
Tall dropseed is a warm-season grass and flowers from August to October [2,24,37,45,94,105,147,224]. In Texas, flowering may continue into November [53]. In tallgrass prairie of central Oklahoma, tall dropseed culms were elongating in sheaths on 30% of quadrats in summer, 46.7% of quadrats in autumn, and 12.4% of quadrats in winter. Fruit formation, exertion of the inflorescence from the sheath, and opening of anthers were only observed in autumn. Dissemination of fruits and seeds was observed on 2.6% of quadrats in autumn and 0.8% of quadrats in winter [2]. In New England, immature fruit was observed on composite dropseed in September (Engstrom personal observation cited in [65]). This publication is a New England conservation and research plan, includes a review focused primarily on composite dropseed, and is cited extensively in this review for information on biological and ecological characteristics [65].

Germination can occur throughout the year [2,22] but may peak in spring [14,25]. In a greenhouse experiment in 1931, 91% of tall dropseed seed planted on 23 April germinated. However, the previous year the maximum germination of 65% occurred with seeds planted 16 September, and none of the seed planted 12 April germinated [22]. Tall dropseed seeds sown in mid-March on a remnant prairie in southwestern Minnesota had much higher germination rates than those sown in winter, although differences in the length of cold stratification before planting may have contributed to the differences (see Germination) [25]. Tall dropseed was one of the more common species germinating from late winter to spring in soil samples collected in November from mixed-grass and weedy meadow communities near Hayes, Kansas [146].

Tall dropseed growth may start in late winter or early spring [144] and peaks later in the growing season [2,224]. On a tallgrass prairie site in central Oklahoma, tall dropseed seedlings (0-1 inch (0-3 cm) tall) emerged on 5.6% of quadrats in summer and 3.1% of quadrats in autumn. "Vegetative growth" of tall dropseed was observed on 6.7% of quadrats in spring, 36.7% of quadrats in summer, 58.5% of quadrats in autumn, and 29.2% of quadrats in winter. Perennating sprouts at soil level were observed on 8.3% of quadrats in winter and were above soil level on 2.2% of quadrats in summer and 1.0% of quadrats in autumn [2]. Phytomass and frequency of tall dropseed were substantially greater in August than in May on 2 sites with differing soils near Saline, Kansas [177].

REGENERATION PROCESSES:

Pollination and breeding system: Reproduction in tall dropseed is predominantly sexual. Although cross-pollination is possible, tall dropseed is primarily self-pollinating [23,187]. Several characteristics, including a sheath-enclosed panicle, restrict the potential for cross pollination in tall dropseed [187].

Seed production: Although variable [23], tall dropseed seed production is generally high [32,50,187]. In little bluestem prairie near Hayes, Kansas, a 3-year study found that tall dropseed averaged 83.4 to 91.3 caryopses per 100 florets. In all years, tall dropseed had the highest average number of caryopses per 100 florets of the 7 grasses measured. In big bluestem prairie in 1941, tall dropseed had the largest seed yield (909.3 lbs/acre) of the 5 grasses investigated [32]. On 3 prairie sites in west-central Minnesota, seed harvesting in September of 1983 yielded approximately 0.51 kg/ha of live tall dropseed seed [168]. Seed production of tall dropseed plants in 2 populations in northeastern South Dakota was variable when grown in a greenhouse over a 3-year period, ranging from 3.8 g of seed/plant to 17.8 g of seed/plant. Tall dropseed from a roadside population averaged 11.9 grams of seed/plant, significantly (P<0.01) more than the 8.1 grams of seed/plant produced by tall dropseed in a native prairie. Seeds from the roadside population were also significantly (P<0.01) larger than seeds from the native prairie [23]. At peak seed set, Stevens [219] collected 4,540 mature seeds from a single tall dropseed plant that was "well developed" and "growing with comparatively little competition." Mississippi dropseed had low seed set following transplanting. It is unclear if this would occur in wild populations [187].

Tall dropseed plants may produce viable seed within a year. On a "prairie reconstruction" site at a Kansas museum, tall dropseed flowered in the first year [178]. According to a review, Weaver and Fitzpatrick (1934) observed tall dropseed produce flowering stalks in the 1st year [65]. Tall dropseed plants germinated in a greenhouse and transplanted to a garden in mid-May produced viable seed in the 1st year [22]. A review notes observations of tall dropseed reaching maturity in the 1st (Bender unpublished) or 2nd year (Christiansen and Landers 1969) [19].

Seed dispersal: The primary mode of tall dropseed seed dispersal has not been reported, although gravity and animals are likely dispersal agents. Tall dropseed may also be dispersed by 'artificial means' such as trains, vehicles, or mowing equipment [65].

Animals likely assist in tall dropseed seed dispersal. Tall dropseed seeds were found in black-tailed jackrabbit (Lepus californicus melanotis) pellets collected in mixed prairie vegetation 2.5 miles west of Hays, Kansas [31] and in bison dung collected from October through December on the tallgrass prairie preserve in Osage County, Oklahoma [192]. In New England, Engstrom observed ensheathed seeds that seem to have been picked open by birds. Although the viability of tall dropseed seeds ingested by a range of wildlife species is not known, seeds collected from black-tailed jackrabbit pellets did germinate in petri dishes and soil (see Germination for more details) [31]. Nearly 1,400 tall dropseed seeds were collected from bison hair samples from a tallgrass prairie preserve in eastern Oklahoma. These seeds were found on only 9 of the 111 hair samples collected [192].

Although mechanism of dispersal was not reported, tall dropseed comprised 2.1% of the seed rain on a native prairie site and 4% on an old field site in Jefferson County, Kansas. These values made tall dropseed the 9th and 5th most common species in the seed rain for each site, respectively [197]

Seed banking: Tall dropseed may be a common component of the seed bank on some sites. Mean tall dropseed seed densities up to 281.1 seeds/m² were observed in west-central Iowa (see table below). Seed bank samples were collected in March, and seeds germinated from the samples from mid-April to mid-August in a greenhouse [194]. Tall dropseed was one of the more common species germinating in a soil sample taken from a mixed-grass habitat near Hayes, Kansas in November. Tall dropseed also germinated from a soil sample taken from a weedy meadow, although it was not common in the aboveground vegetation of that community [146]. Viable tall dropseed seed occurred in soil samples collected in May in both native prairie and old field sites in Jefferson County, Kansas. It was the least abundant species in the native prairie soil seed bank (0.4% relative abundance) and one of several uncommon species in the seed bank of the old field site (2.7% relative abundance) [197].

Tall dropseed occurrence in the seed bank and vegetation of several communities on 2 sites in Monona County, Iowa [194].
Site description Community Mean seed density (seeds/m²) Percent of seed bank Relative occurrence (index based on basal cover)
Site 1: 18 years of fire management; north- and south-facing aspects Midgrass (n=6) 281.1 38% 2%
Nonnative grassland (n=2) 91.7 6.3% 0.6%
Tallgrass prairie (n=5) 80.7 8.2% 0.2%
Deciduous woodland community (n=7) 2.6

<0.01%

--*
Deciduous shrubland communitieis 0.0 0 --
Site 2: 11 years of fire management; east-, northwest-, and southwest-facing aspects Eastern red-cedar woodland (n=5) 3.7 <0.01% --
Nonnative grassland 0.0 0 --
Post-settlement woodland 0.0 0 --
Post-settlement shrubland 0.0 0 --
*values not given

As of late 2009, longevity of tall dropseed seeds in the soil seed bank has not been reported but some dormancy may occur. Germination of unfrozen seeds collected in 1931 and planted in 1932 was 91%, while no seeds harvested in 1921 and sown in the spring of 1930 germinated [22]. Germination rates of tall dropseed seeds in greenhouse experiments increased from 16% after more than 2 years of dry storage to 67% following more than 5 years of dry storage.

Germination: Tall dropseed seeds may experience a period of dormancy that is broken by cold temperatures (Toole 1941 cited in [15]). Tall dropseed was considered a polycarpic perennial with peak germination in spring by Baskin and Baskin [14]; this group of species generally requires a period of cold temperatures for seeds to after-ripen. Germination rates of tall dropseed seeds sown on a remnant prairie in southwestern Minnesota increased with exposure to cold, moist pretreatment. Germination after 30 days was 6% for seeds exposed to 39 °F ( 4 °C) on a moistened surface for 6 weeks, 44% for seeds exposed for 9 weeks, and 96% for seeds exposed for 15 weeks. Timing of planting may have contributed to differences in germination rates, because seeds exposed to cold temperatures for 15 weeks were planted in spring while the others were planted in winter [25]. In the few cases where direct comparisons could be made, tall dropseed seeds sown in winter that were not frozen had slightly to much higher germination than frozen seeds [22]. Tall dropseed seeds that were over 7 months old did not require cold pretreatments to germinate at room temperature, at temperatures alternating between 36 °F and 54 °F (20-30 °C), or at temperatures alternating between 27 °F and 54 °F (15-30 °C) [187]. None of the tall dropseed seeds harvested in autumn from a prairie site in west-central Minnesota were dormant [168].

Several factors may influence tall dropseed germination rates including age of seed [22], time of planting [22,25], environmental conditions [25], and variety [187]. Documented germination rates range from less than 10% [22,25,65] to more than 90% [22,25]. Several tall dropseed germination trials in a greenhouse resulted in 0% germination. In the same experiment, 65% of seeds planted in September 1930 germinated, 60% of those planted in December 1930 germinated, and 91% of those planted in April 1931 germinated [22]. Tall dropseed seeds collected from a prairie in west-central Minnesota exhibited a 40% germination rate [168]. Germination rates may be lower for Mississippi dropseed than the other 2 varieties [187]. Seeds collected from black-tailed jackrabbit pellets and planted in soil showed a germination rate of 40%; seeds hand-picked on a mixed-grass prairie site near Hayes, Kansas showed a germination rate of 70% [31].

Seedling establishment and plant growth: Tall dropseed can quickly establish on open sites. High seed production, good viability, and aspects of tall dropseed seedling morphology promote rapid colonization of open sites [50], including disturbed areas [26]. Vinton and Burke [239] note that tall dropseed is a productive bunchgrass.

Tall dropseed seedlings may be drought tolerant. In a greenhouse experiment all tall dropseed seedlings in 4 inches of moist soil survived 15 days without water and 2 consecutive periods of drought lasting 17 and 13 days. Twenty percent of tall dropseed seedlings in 3 inches of moist soil survived 17 or more days without water [157]. However, of the 3 or 4 tall dropseed seedlings planted in a lowland prairie near Lincoln, Nebraska, none survived a late summer drought in 1931 [22].

Tall dropseed plants may live over 20 years. In a study tracking the survival of perennials on plots near Hayes, Kansas, from 1932 to 1972, 37% of tall dropseed survived from the 1st to 2nd year, and life expectancy in the 1st year was 3.51 years. Older tall dropseed plants had higher survival rates [140].

Vegetative regeneration: Few details regarding vegetative regeneration of tall dropseed were available as of 2009. Tall dropseed reproduces from tillers and, in the case of Mississippi dropseed, from rhizomes [224] (see Botanical description). A 1934 article described the rhizomes as "vigorous" [37].

SITE CHARACTERISTICS:
Tall dropseed occurs on many site types, including plains [55,56,57,103], foothills [45,104,105,224], hills [55,56,57,103], and beaches [65]. In eastern Colorado, it occurs in piedmont valleys and outwash mesas [251]. It is also common on disturbed sites including old fields [79,106,107,254], roadsides [11,65,94,147], and railroad rights-of-way [11,65]. For information on species associated with tall dropseed in the prairie, savanna, and disturbed habitats it occupies, see Habitat Types and Plant Communities.

Tall dropseed tolerates a wide variety of climatic and edaphic conditions [50] and therefore occurs on sites with variable microclimate, moisture availability, elevation, soil, and topography. Tall dropseed shows a general trend of increased importance with decreasing latitude from northern prairies of the Dakotas, Minnesota, and northern Iowa to southern prairies [51,188]. Varietal differences in site preferences may explain some of the variation in relationships to site characteristics including soil depth [3,60], soil texture [65,103], and topography [60]. More detailed descriptions of these trends are not feasible because of confusion over the synonymy between previously recognized varieties and currently recognized varieties.

A New England conservation and research plan that includes a review focused primarily on the biology and ecology of composite dropseed [65] is cited throughout in the following sections.

Moisture regimes: Tall dropseed generally occurs on relatively dry sites in the eastern United States and relatively mesic sites in the western United States. Note that the definitions of soil moisture descriptions are not consistent among studies, making comparisons of studies and identification of patterns difficult. Tall dropseed occupies some of the driest habitats of New England, such as well-drained sands and rock uplands [65]. However, it also occurred in a rare wetland community in Ontario, the perched prairie fen (Ontario Natural Heritage Information Centre 1996 cited in [65]). Tall dropseed did not occur on mesic prairies in Iowa but was present on comparatively dry prairies of Nebraska and Kansas. In this region it occurred on a greater number of bluestem prairies than somewhat drier wheatgrass prairies [249]. In Colorado, tall dropseed occurred in a tallgrass prairie community that was limited to lowlands with coarse soils and high water tables [42], and in Utah it ocurred in dry soil along a stream [211].

In the central United States, tall dropseed occurs on sites with a range of moisture regimes. Tall dropseed was a characteristic species of 5 mesic vegetation types in southeastern Texas [154] and was listed as typical of wet-mesic and mesic sites of tallgrass prairies in a review [130]. It is a component of west-central Louisiana prairie that occurs on mesic, dry-mesic, and dry sites [162]. The tall dropseed-little bluestem-big bluestem community was the most xeric grassland type in the tallgrass Blackland Prairie in Texas [38]. In mixed-grass prairie of south-central Nebraska, tall dropseed occurred at a basal cover of 5.3% on steep, dry slopes with rapid runoff [195]. In northwestern Kansas and southwestern Nebraska, tall dropseed comprised just over 2% of the vegetation on a dry-mesic site and less than 1% of the vegetation of a dry site. It did not occur on the mesic or the very dry site. Moisture classifications in this study were subjective and based on slope, position on the slope, and exposure [112]. Tall dropseed basal cover was only 0.2% in shortgrass prairie on a dry upland site in central Kansas with low soil permeability and southern exposure [111].

See Climate for information on precipitation trends on sites with tall dropseed and its tolerance of drought, and Soil for information on soil characteristics that affect moisture availability on sites with tall dropseed.

Elevation: Elevations of sites with tall dropseed range from below 500 feet (150 m) in coastal states [49,65,162,184,242] to over 6,500 feet (2,000 m) in the Southwest [72,136]. In New England 90% of composite dropseed occurrences were below 500 feet (152 m), and it occurred at a maximum elevation of 900 feet (274 m) in Connecticut [65]. Tall dropseed occurs at similarly low elevations in Mississippi [242], Louisiana [162], and coastal Texas [49]. Sites where it occurs in the Great Lakes and Great Plains regions range in elevation from about 350 to 2,440 feet (106-744 m) [62,173,174,185,188,205,227,254,256]. In the Southwest, tall dropseed is reported at higher elevations [72,136,211]. The table below provides elevations of some sites where tall dropseed occurs.

Elevations of sites with tall dropseed grouped by region
Region State Elevation
New England Maine 460 feet (140 m) [184]
Lake States Illinois 607 feet (185 m) [173]
348-361 feet (106-110 m) [62]
Minnesota 1,680 feet (512 m) [254]
North-central North Dakota 878 feet (268 m) [185]
South Dakota ≈2,414 feet (736 m) [145]
2,441 feet (744 m) [205]
Kansas 1,063 feet (324 m) [174]
2,343 feet (714 m) [205]
South-central Oklahoma 1,286 feet (392 m) [205]
1,230 feet (375 m) [188]
Arkansas 830-945 feet (253-288 m) [118]
Texas 1,100-1,300 feet (335-396 m) [227]
1,200-1,395 feet (365-425 m) [256]
Texas (coastal) up to 250 feet (75 m) [49]
Southeast Louisiana 150-250 feet (50-75 m) [162]
Mississippi 230 feet (70 m) [242]
Southwest Utah 4,530 feet (1,380 m) [211]
Arizona 6,560-7,530 feet (2,000-2,295 m) [136]
New Mexico 7,198 feet (2,194 m) [72]

Climate: Tall dropseed occurs over a range of climatic conditions but may be more abundant in areas of greater precipitation and warmer temperatures. Based on 63 sites from North Dakota to Texas, tall dropseed frequency was positively correlated with annual precipitation (P<0.002) and maximum and minimum temperatures (P<0.0001) [51].

Length of the frost-free period on sites with tall dropseed ranges from 125 days to 330 days. In more northern portions of its range examples of frost-free periods on sites with tall dropseed range from 125 days in eastern North Dakota [185] to 171 days in east-central Illinois [173]. From southern Illinois [62] into Oklahoma [150,252] and Texas [227,256] the frost-free period is often over 200 days, and areas of eastern and southeastern Texas have frost-free periods ranging from 250 [50] to 330 [49] days.

Temperatures on sites with tall dropseed vary from average minimum temperatures of 16.2 °F (-8.8 °C) occurring on an Arizona site to average maximum temperatures in Texas of about 95 °F (35 °C). The table below indicates temperature patterns on sites where tall dropseed occurs, although these may not be optimum conditions for tall dropseed.

Average minimum and maximum temperatures on sites with tall dropseed
Location Average minimum temperature (°C) (January) Average maximum temperature (°C)
(July unless otherwise noted)
Central Ohio -3 24.6 [128]
Stillwater, Oklahoma -4.3 34 (Aug) [150]
Central Texas -5 35 [256]
Eastern Texas Northern: 1
Southern: 6
≈ 35 [50]
Arizona -8.8 29.3 [136]

Average annual precipitation on sites with tall dropseed ranges from about 8 inches (200 mm) on a site in New Mexico [72] to 59 inches (1,500 mm) in Mississippi [242]. Seasonality is also variable, although a large proportion often falls in the growing season [4,30,62,112,128,145,150,174]. Peak precipitation on sites with tall dropseed occurs in April in Illinois [173], April and May in the western cross timbers of north-central Texas [60], and late summer or autumn on a site in southeast Texas [169]. Precipitation peaks twice, in spring and autumn, in southeastern Texas [9,49,154,227]. Reported average snowfall on sites with tall dropseed include 40 inches (1,008 mm) in eastern North Dakota [185], 38 inches (973 mm) in Arizona [136], 19.6 inches (498 mm) in Hayes, Kansas [4], and 2 to 4 inches (50-100 mm) in the western cross timbers of northern Texas [60].

Mean annual precipitation on sites with tall dropseed grouped by region
Region Mean annual precipitation
Ohio and Illinois 34 to 42.5 inches (864-1,080 mm) [62,128,173]
Eastern North Dakota south to the Nebraska-Kansas border 14.7 to 30 inches (374-760 mm) [30,112,145,185]
Manhattan, Kansas about 33 inches (835 - 840 mm) [159,174]
Oklahoma 23.5 to 37.6 inches (597 - 955 mm) [150,159,252]
North-central Texas 23.6 to 27.6 inches (600-700 mm) [9,60,227,256]
East-central Texas 29.5 to 45.3 inches (750-1,150 mm) [38]
Southern Texas 35.4 to 47.2 inches (900 -1,200 mm) [49,154,169]
Louisiana and Mississippi 50 to 59 inches (1,270-1,500 mm) [162,242,253]
Arizona 17.5 inches + 38.3 inches snowfall
(444 mm +973 mm) [136]
New Mexico 5 to 9 inches (130-230 mm) [72]

Tall dropseed is considered one of the most drought-tolerant tallgrass prairie species [157] and may increase in conspicuousness [213,222] and cover [5,152,191] during periods of drought in these communities. Greenhouse experiments on the drought tolerance of tall dropseed seedlings (see Seedling establishment) and experiments on responses to atmospheric drought resulted in tall dropseed being ranked 4th out of 14 species for drought tolerance, following 3 short grasses [157]. Although tall dropseed declined on a few sites in Nebraska and Kansas during the extreme drought of the 1930s [191], overall cover of tall dropseed increased [5,191]. On sites in southeastern Nebraska and northwestern Kansas, tall dropseed cover increased by 44.5%. On some of these sites tall dropseed continued to flower during the drought [191]. On an upland bluestem range in Kansas, tall dropseed reached its peak cover of 5% during a drought [152]. Several authors assert tall dropseed's drought tolerance [101,120,224,246]. However, on a site in western Oklahoma tall dropseed was described as "not very drought tolerant" [99], and a study of 63 sites from North Dakota to Texas demonstrated a positive association between tall dropseed frequency and annual precipitation [51].

Site characteristics likely influence tall dropseed's response to drought. In Texas, tall dropseed increased with increasing precipitation on Vertisols with 2% sand, 37% silt, 61% clay receiving 34 to 45 inches (860-1,150 mm) precipitation. In contrast, tall dropseed generally declined with increasing precipitation on a site with shallow, carbonatic Mollisols comprised of 2% sand, 43% silt, and 55% clay that received 30 to 37 inches (750 to 950 mm) of precipiation [38]. In mesquite/mixed-grass communities tall dropseed increased with increasing precipitation [6,169].

Soil: Tall dropseed tolerates a wide range of soil characteristics [99]. Soil moisture availability, and characteristics such as drainage, permeability, and water holding capacity on sites with tall dropseed are variable. It occurs in shallow to deep soils of various textures. Soil pH on sites with tall dropseed varies from acidic to alkaline. Tall dropseed may be associated with calcareous soils in some areas.

Tall dropseed has been reported on nonsaline soils in eastern North Dakota [185] and, according to a review [65], also occurs on sites with high salinity. Examples of sites with high salinity occupied by tall dropseed include seashore habitats in New England and Virginia, a granite boulder in a tidal river marsh in Massachusetts, saline seeps in Missouri, and roadsides where salt is used for deicing in winter [65]

Tall dropseed may be associated with soils with little organic matter. Based on 63 sites from North Dakota to Texas with organic matter contents ranging from 3% to over 9%, tall dropseed was negatively correlated with percent soil organic matter (P<0.0002) [51]. However, Vinton and Burke [239] suggest that the productivity of tall dropseed may contribute to large amounts of organic matter. In a tallgrass prairie remnant of southeastern Texas, tall dropseed was characteristic of 5 mesic vegetation groups which had average percent organic matter from 3.0% to 4.7%. Organic matter of all sites in this study ranged from 2.6% to 5.0% [154].

Soil moisture availability: Several sources note tall dropseed's occurrence in "dry soils" [45,104,211,224], although it may be most common on sites that are "intermittently wet and dry" [144,224]. Tall dropseed had the 3rd highest importance value in a Muhlenbergia grassland in eastern North Dakota that occurred on sites that occasionally approached the permanent wilting point (-1.5 MPa) by 21 August [185].

Soils on sites with tall dropseed have varying drainage, permeability, and water-holding capacity. Tall dropseed has been documented on sites with poorly drained soils [13,142,169] and has been reported in several communties on sites with well-drained soils [62,142,154,162,165,253]. Soil permeability descriptions range from "very slow" on a tallgrass prairie site with 13.7% cover of tall dropseed in Texas [214] to "moderate" on a Texas Ashe juniper site [256], and as "absorbing water readily" in the loessial region of northwestern Kansas and southwestern Nebraska [112]. On some sites with tall dropseed, clay decreases infiltration of water into lower soil layers (e.g., [111,190]). Reported water-holding capacity of soils on sites with tall dropseed include poor [190], moderate [256], moderately high [112], and good [190]. South-central Nebraska mixed-grass communities with tall dropseed ranged from having low water-holding capacity due to underlying bedrock to having moderate to high water-holding capacity on a lowland range site [195].

Depth: Tall dropseed occurs on sites with varying soil depths [142,153,165]. On the Edwards Plateau in Texas, tall dropseed occurred on bottomland sites with clay up to 7 feet (2 m) deep and sites on plateaus and upper slopes with shallow soils 12 to 14 inches (30-35 cm) deep [153]. In north-central Texas, tall dropseed occurred in mixed-grass communities on sites with soils 10 to 13 feet (3-4 m) deep [9] and in an Ashe juniper-mixed grass community on sites with 6 to 12 inches (15-31 cm) of soil over cracked limestone [256]. Drummond's dropseed occurred on deep alluvial soil in west-central Kansas [3] and deep clays receiving run-in water in Texas [60], while composite dropseed occurred on comparatively shallow soils on these study sites [3,60]. Tall dropseed has been reported in shallow soils in Kansas [4,190] and Arkansas [118] and shallow soil over limestone in Oklahoma [106]. Tall dropseed and prairie threeawn codominated on a grazed site with "extremely shallow soil" in Kansas [190].

Texture: Although often associated with sandy soils [45,104,105,147], tall dropseed is not limited to soil of any particular texture. In the Great Plains, tall dropseed occurs on sites with soils ranging from sands [60,208,242,252] to loams [30,128,245] to clays [60,145,190,256]. Reported soil textures on sites with tall dropseed range from sand to clay in Texas [9,60,169,208,256], from sand to silty clay in Oklahoma [92,150,205,252], and silt loam to silty clay loam in Kansas [112,126]. In eastern Texas tall dropseed was a secondary graminoid that occurred in all 35 stands sampled and did not have any significant correlation with percent clay, which apparently ranged from 24% to 68% [50]. In tallgrass prairie remnants of southeastern Texas, tall dropseed was characteristic of 5 mesic vegetation groups which had average percent sand ranging from 26.4% to 46% and average percent clay ranging from 27.6% to 53.7% [154]. In New England, composite dropseed is most common on sandy sites including beaches. In Ontario, tall dropseed occurs in fens that develop on gravel slopes, and in Quebec it was reported on the rocky shore of the St. Lawrence River [65]. Tall dropseed was found in "stony alluvium" and crevices within bedrock along the Aroostock River in Maine [184]. According to a flora, Drummond's dropseed may be associated with rocky hills [103].

pH: Sites with tall dropseed have been reported to have soil pH as low as 4.6 in the Arkansas Ozarks [118] and as high as 8.1 in northwestern Kansas and southwestern Nebraska [112]. In eastern Texas tall dropseed was not significantly correlated with pH on the 35 stands sampled which apparently had soil pH values ranging from 4.9 to 7.4 [50]. It has been reported on acidic to neutral soils (pH range 4.6-6.9) in Kentucky [245], the Arkansas Ozarks [118], Kansas tallgrass prairie [87], coastal areas of southern Texas [49,154,161], and the western cross timbers in Texas [60]. Soil pH on 3 mixed-grass communities with tall dropseed in south-central Nebraska ranged from 6.5 to 7.3 [195]. Tall dropseed has been documented on basic soils (pH range 7.3-8.1) on an abandoned mine site in New Mexico [72] and grasslands of Wisconsin [65], eastern North Dakota [185], Nebraska [112], Kansas [111,112], Texas [38], and west-central Louisiana [162].

Calcium: Tall dropseed commonly occurs in areas with substantial calcium in the soil and/or over calcareous parent material, although it also occurs on sites with noncalcareous soils [153]. Composite dropseed distribution was associated with calcareous bedrock formations in western New England and, according to a review, occurred in a Wisconsin prairie community with calcium concentrations of 5,000 ppm or greater [65]. Tall dropseed has been reported on sites with calcareous soils in Montgomery County, Alabama [244], west-central Louisiana [162], the gulf coastal plain of Texas [161], a rare fen community in Ontario [65], an Ohio prairie [128], and a prairie community in Mississippi [163]. Tall dropseed had 5.3% basal cover in a mixed-grass prairie community that occurred on limy range sites associated with calcareous uplands in south-central Nebraska [195] and was a component of prairie openings in the Mississippi gulf coast plain associated with calcareous outcrops in clay sediments [253]. Tall dropseed occurred on sites where soils overlay limestone in little bluestem-sideoats grama vegetation in Cocktaw County, Oklahoma [106] and in the northern Great Plains [121]. Tall dropseed is a species of limestone glades that occur in the Midwest, Illinois [16], Alabama [17], and the Missouri Ozarks [164]; and it occurred in a open woodland community associated with limestone, dolomite, or calcareous shale parent material in Tennessee [165]. Tall dropseed was a component of a tallgrass prairie community of the Flint Hills that occurred on soils formed in shale and/or limestone [142].

Topography: Tall dropseed occurs along rivers and streams, in other lowlands, on hillsides, and in uplands. Tall dropseed occurs in riparian areas in Nebraska [121], Utah [211], New England [65,184], and Canada [33,65]. It was a secondary species in an oak savanna community occurring in steep areas along rivers and streams in Texas [236]. Tall dropseed was a component of a tallgrass prairie community that occurred in swales near Hayes, Kansas [140]. In one tallgrass prairie site in northeastern Kansas, tall dropseed was less common in upland soils than lowland soils [82]. However, in annually burned sites in this same area, tall dropseed had average frequencies of 100% on upslope positions, 70% on slope bottoms, and near 0% in lowlands [85]. Tall dropseed reached its greatest frequency in areas with 0 to 3% slopes compared to sites on gentle (1-10%) or steep (11-24%) slopes in northwestern Kansas and southwestern Nebraska [112].

Most sites with tall dropseed have flat to undulating topography, but tall dropseed probably also occurs on steep slopes. Tall dropseed occurs on relatively level sites (0-12% slope) in Texas [169,214], Kansas [174], and Nebraska [30]. In northwestern Kansas and southwestern Nebraska tall dropseed occurred in level areas and on gentle slopes, but not on a steep upper slope [112]. Tall dropseed has been reported on sites with a wide range of slopes, although occurrence of tall dropseed on the steepest slopes on these sites is uncertain. This includes an Ashe juniper community on a site in Texas with slopes from 0% to over 20% [256], a mixed-grass prairie site in south-central Nebraska with slopes of 3% to 31% [195], 4 savanna-glade-woodland sites in the Ozarks with slopes ranging from 7% to 49% [118], an oak savanna site with slopes ranging from 12% to 30% in Texas [236], and a severely burned ponderosa pine woodland site with slopes ranging from 17% to 45% in Arizona [136]. In the Arkansas Ozarks, tall dropseed occurred in the savanna-glade-woodland mosaic on 4 sites with eastern, southern, southwestern, and northwestern aspects [118].

SUCCESSIONAL STATUS:
Tall dropseed has been well studied in the tallgrass prairies at the Konza Prairie Biological Station in the Flint Hills of northeastern Kansas, just south of Manhattan. Throughout the remainder of this review this area is referred to as the Konza prairie.

Tall dropseed is generally associated with mid- and late-successional tallgrass prairies, although it may occur on recently disturbed sites. Tall dropseed occurred in late successional tallgrass prairie communities of Texas [167] and Oklahoma [64]. In a mesquite/mixed-grass community in Texas tall dropseed was considered a mid- to late-successional species [6]. Following abandonment of prairie dog towns in southwestern Oklahoma, tall dropseed did not occur in the earliest successional stages. It occurred at trace levels in intermediate successional stages dominated by threeawn and in the "climax" tallgrass stage [170]. Of 6 successional stages recognized on a site in Kerr County, Texas, tall dropseed occurred in the late-successional "perennial tallgrass or grama stage" with sideoats grama, little bluestem, blue grama, hairy grama (Bouteloua hirsuta), and silver bluestem (Bothriochloa saccharoides) [35]. In the grand prairie region of Texas, tall dropseed was listed as a midgrass, an important component of late-successional communities on shallow soils or grazed sites [208]. On Konza prairie sites with deep soil that had been recently burned (≤3 years prior), tall dropseed stem density was positively correlated with weight of standing dead herbaceous vegetation (P=0.043) [54].

Despite a general absence from early successional communities in the areas described above, tall dropseed may occur on recently disturbed sites. Tall dropseed in southeastern Iowa was described as establishing "relatively soon after disturbance" and colonizing "noncompetitive plant communities quite quickly" [26], and is often reported on disturbed sites such as old fields and roadsides (See Habitat Types and Plant Communities). Rate or timing of establishment on these sites is not documented. Type and severity of the disturbance likely influences the length of time required for tall dropseed to establish. See Management considerations and Fire effects for information on responses to specific disturbances.

Light: Based on characteristics of sites occupied by tall dropseed, it seems reasonable to infer that tall dropseed is intolerant of shade. It rapidly colonizes open areas in eastern Texas [50]. In New England, tall dropseed occurred only on sunny sites [65]. In experiments testing which factors associated with fire influenced plant responses at Konza prairie, tall dropseed biomass was lower on a burned-and-shaded plot than on plots exposed to other treatments and a control plot that was not shaded. It is not clear whether differences in tall dropseed biomass were significant because it was grouped with several other grass species for statistical analysis [110].


FIRE EFFECTS AND MANAGEMENT

SPECIES: Sporobolus compositus
FIRE EFFECTS:

Immediate fire effect on plant: As of late 2009, no information was available on the immediate effects of fire on tall dropseed. Tall dropseed may survive and sprout tillers after fire (see Vegetative regeneration). Mississippi dropseed has rhizomes that may survive fire; however, information on morphology and depth of Mississippi dropseed rhizomes is lacking (See Botanical description). Postfire survival of tall dropseed is likely related to the amount and condition of litter accumulated in tufts and the resulting fire severity (see Fuel condition).

Tall dropseed seeds and/or seedlings may be more vulnerable to fire than established plants. Although tall dropseed was ranked fourth in late season ramet emergence in an annually burned prairie, tall dropseed seedlings did not occur on these sites [20]. Tolerance of seedlings to temperatures up to 145 °F (63 °C) was tested in a greenhouse with generally high survival rates that varied with exposure time and seedling age. All 5-week-old seedlings survived 9 hours of exposure to hot wind up to 145 °F, while 64% of 3 week-old seedlings survived 4 hours of exposure to temperatures of 140-153 °F (60-67 °C) [157].

Postfire regeneration strategy [220]:
Rhizomatous herb, rhizome in soil (Mississippi dropseed, only)
Tussock graminoid

Possible:
Ground residual colonizer (on site, initial community)
Initial off-site colonizer (off site, initial community)
Secondary colonizer (on- or off-site seed sources)

Fire adaptations and plant response to fire:

Fire adaptations: As of late 2009 there was little information in the available literature on tall dropseed's fire adaptations. Tall dropseed reproduces from tillers as well as seed (see Regeneration Processes). Mississippi dropseed has rhizomes (See Botanical description) that have been described as “vigorous” [37]. Postfire sprouting from tillers or rhizomes would allow tall dropseed to persist and possibly spread in the postfire environment; however, its postfire response likely depends on a number of other factors (see Plant response to fire).

The potential for abundant seed production, seed banking, and favorable conditions for tall dropseed germination and seedling establishment in the postfire environment suggests that it may establish from on-site seed following fire. Fire can be effective in reducing litter, raising soil temperatures [215,237], increasing light levels, releasing nutrients [215], and increasing plant productivity in tallgrass and southern mixed-grass prairies [215,237], all of which favor seedling germination and establishment. However, it is unclear whether and under what conditions tall dropseed seeds survive fire. Tall dropseed seeds germinated from soil samples collected from west-central Iowa prairie sites with a nearly 18-year history of fire management, and from an eastern redcedar woodland with a 10-year history of fire management [194]. No details were provided regarding the type of fire management used, such as season or frequency of burning.

Dispersal by animals may allow for postfire establishment from off-site seed sources; however, this has not been documented in the literature as of late 2009.

Plant response to fire: Postfire responses of tall dropseed documented in the literature are not consistent; it has been observed to increase [27,28,81,84,175], decrease [39,81,84,160,227,231,232], and remain unchanged [82,143,180,193,202] in the postfire environment. Tall dropseed postfire survival, persistence, and spread are likely influenced by a number of interacting factors including fire and fuel characteristics, fire history, site conditions that influence moisture and nutrient availability (e.g., soil type and topography), plant community composition, presence of grazing animals before and after fire, management history, and postfire management. It is not always clear from the available literature which of these factors most strongly influences tall dropseed postfire response in a given situation. However, it appears that tall dropseed is most likely to increase after infrequent fires (fire-return intervals >2 years) in early spring on comparatively mesic sites, or in periods with high precipitation. Tall dropseed may have greater tolerance of annual burning in grazed areas.

Although several studies include information on tall dropseed's response to fire, none are focused exclusively on tall dropseed, and individual studies are limited in various ways. Limitations include varying amounts of information on confounding factors, few replicates or controls, small sample sizes, differences in timing of vegetation sampling relative to fires, comparison of multiple simultaneous treatments, and/or anecdotal evidence. Many studies report responses of a group of species that included tall dropseed [7,21,98,149], such as warm-season and/or perennial grasses [47,66,67,89,217] or midgrasses [226,229]. Results from 3 of these studies [149,217,229] are included in the discussion below. Studies that investigate community-level responses to fire in areas where tall dropseed occurs include Collins and Smith [40], Dai and others [47], Fuhlendorf and Engle [77] and/or Risser and Parton [189]. Community-level responses from these studies are not discussed in this review.

Fire frequency: Single fires apparently have little impact on tall dropseed abundance. On a pasture in the Edwards Plateau near Johnson City, Texas, tall dropseed cover on experimental plots burned on 25 August or 28 October of 2004 did not differ significantly (P>0.05) from each other or from unburned plots a year later [202]. On a central Oklahoma rangeland, average tall dropseed frequency in December did not differ significantly (P>0.05) on unburned sites and sites burned in late March [180]. In Pinchot's juniper-dominated rangelands of northwestern Texas, frequency of tall dropseed did not differ significantly (P>0.05) between a site burned 4 years previously in spring, a site burned 8 years previously in spring, and an unburned control site [143]. In one Konza prairie study differences in stem density of tall dropseed on sites burned a few months, 1, and 3 years previously were not significant [54]. On Konza prairie sites burned in late April 1981 or early May 1982, tall dropseed flower stalk density and height at the end of the growing season of the fire year were not significantly different from unburned sites. However, biomass on unburned sites was lower than on burned sites in both 1981 and 1982. Tall dropseed total oven-dried mass was 7.2 g/m² and 10.0 g/m² on burned sites, and 2.7 g/m² and 1.8 g/m² on unburned sites in 1981 and 1982, respectively. The combined aboveground biomass of tall dropseed, big bluestem, indiangrass, little bluestem, sideoats grama, and switchgrass was significantly (P<0.01) greater on burned than unburned sites in both years [110]. In tallgrass prairie near Stillwater, Oklahoma, tall dropseed phenological development in May, June, or July did not differ significantly between control plots and plots treated with herbicide and burned in late spring. Comparisons between treated and control plots were not made in August or September [24].

Repeated fires at intervals greater than 1 year also seem to have little impact on tall dropseed. In pastures of southern Iowa, tall dropseed showed no significant changes in biomass or relative shoot frequency up to a year following burning treatments in March or April. This included plots burned twice in 3 years [193]. On Kansas prairie sites that had been burned 4 times in 6 years, tall dropseed frequency ranged from 50.0% to 75.0% and biomass ranged from 14.9 to 29.7 g/m² in August [177] (see Soils/topography for details). On the Konza Prairie, tall dropseed was not noticeably impacted by spring burning every 4 years [82] and was a subdominant on a winter-grazed area north of Manhattan, Kansas, burned 2 to 3 times in 10 years [174]. Tall dropseed was the only native grass in a southwestern Minnesota old field burned every 3 to 4 years over a period of about 18 years [254]. In contrast, in mixed-grass or tallgrass prairie in Iowa, tall dropseed did not occur on plots that were burned 1 to 3 times in 8 years or on grazed-and-burned plots, despite occurring at low frequency on grazed-only plots [34].

Annual burning: Although tall dropseed occurs in some annually burned prairies, most evidence suggests that tall dropseed abundance may be lower on annually burned sites. This may not be the case in grazed areas (See Interactions between fire and grazing), and the effects of annual burning likely depend on several other factors including fire season, species composition, and prefire and postfire precipitation. In tallgrass prairie sites in central Oklahoma, cover of tall dropseed in June ranged from 12.9% to 17.4% on unburned sites compared to 3.7% to 6.1% on sites burned in annually April. The declines in tall dropseed cover following the 2nd and 3rd annual burns on this site were significant (P<0.05). Grazing occurred on a subset of both the burned and unburned sites but did not have a significant influence on tall dropseed's response to fire [39]. Although variable over the course of a 5-year study near Stillwater, Oklahoma, tall dropseed frequency on a site that was burned every spring from 1984 to 1988 was significantly (P<0.05) lower in 3 of 4 summers following the third annual burn compared to the July after the second burn [92]. Towne and Kemp [232] found tall dropseed cover was significantly lower after 8 years of annual burning than following the first burn on the Konza prairie, regardless of season of burning or topographic position, while frequency was significantly higher on sites burned annually in winter. Perhaps seedling establishment increased with annual burning in February, while vigor of sprouters was reduced with annual burning regardless of season.

Cover*/frequency (%) of tall dropseed in 2001, following 8 years of annual burning, in 3 different seasons and 2 topographic positions [232].
Burn season Late November Mid-February Late April
Uplands 0.8/85 2.0/95+ 0.9/75
Lowlands 4.8/97.5 2.5/97.5+ 0.9/90
*All cover values are significantly (P<0.05) lower than tall dropseed cover following the first burn.
+ indicates a significant increases in tall dropseed frequency between 1994 and 2001

Gibson and Hulbert [86] found a weak but positive association between tall dropseed cover and time since fire on the Konza prairie. Other studies at Konza prairie found similar results. Tall dropseed was never a dominant species on annually burned sites. It occurred as a codominant less often on plots burned annually for at least 5 years than on plots that had not been burned in 3 years [88]. Tall dropseed did not occur on a site burned in spring for 4 consecutive years but comprised 5% of the relative cover on a site burned 2 years previously [78]. No tall dropseed seeds germinated from soil samples collected from a Konza prairie watershed burned annually in April, an average of 0.2 tall dropseed seedlings emerged from 1,352-cm² soil samples collected from a watershed that had been burned from 2 to 6 years previously, and an average of 1.3 tall dropseed seedlings emerged from 1,352-cm² soil samples collected from a watershed that had not been burned in about 12 years. Tall dropseed cover was less than 5% on all of these sites and may have been absent from some sites [1]. At the end of the 2000 growing season, no tall dropseed seedlings were observed on a plot burned annually since 1996, while an average of about 0.5 tall dropseed seedling/m² occurred on a plot last burned in 1991. Tall dropseed ramet density was similar on annually and infrequently burned plots [20].

In some cases, tall dropseed has greater occurrence on annually burned sites than less frequently burned areas. Tall dropseed was referred to as an important species of annually burned sites on the Oklahoma Agricultural Experiment Station Research Range near Stillwater, Oklahoma [150] and was 1 of the 12 most common species on annually burned sites in the Konza prairie [124]. In the Konza prairie, tall dropseed cover ranged from 5% to 11% on sites burned every 1 or 2 years, while cover in areas burned 3 or more years apart ranged from 1% to 5% [240]. Additional data from the Konza prairie suggests that tall dropseed cover and frequency were higher on sites burned annually in November and March than on sites burned annually in late April, sites burned every 2 years, or unburned sites; however, no statistical comparisons were made. This report includes cover and frequency data from areas with varied fire frequencies, seasons of annual fires, and soil characteristics. Data are presented in the table below and are referred to in other portions of this review [84]:

Maximum percent cover/percent frequency of tall dropseed measured from late spring to late summer on plots with different soil types and burning treatments in Konza prairie. The number of replications for each treatment is in parentheses [84].
Fire frequency
Fire season (month)
Site Characteristics
Silty clay soils on foot slopes
Cherty silt soils on upper rim of slopes
Annual November 13/72 (2) 24/100 (1)
March 25/95 (2) 22/90 (1)
Late April 0.2/10 (3) 5.5/28 (3)
2-year interval April 0.9/17 (3) 0.2/7 (3)
4-year interval April 15/65 (2) 2.2/28 (2)
Unburned N/A 3.0/25 (2) 0.7/15 (3)

Fire Season: Although responses are variable, fires in the early spring may benefit tall dropseed, while fires following emergence of tall dropseed in late spring (see Seasonal development) may be detrimental. As of late 2009, little information is available on tall dropseed’s response to summer [81,229] or autumn fires. Limited data suggest tall dropseed response to autumn fire is variable. Impacts of winter fires on tall dropseed are variable but generally small [28,81,175,232].

Tall dropseed generally responds positively or neutrally to early- and mid-spring burning [81,110,175,180], with neutral or negative responses more likely following late-spring burning [84,232,233]. One possible explanation for this trend is that the reduction of mulch by fire in early spring results in warmer soils and greater grass production earlier in the year [52]. Additionally, fires in late spring may be more likely to damage tall dropseed than fire in other seasons, because it is typically dormant in early spring and emerges in mid to late spring (see Seasonal development).

Some studies show no change [110,175,180] or an increased abundance [81,110] of tall dropseed after early spring fires, and some show differences in tall dropseed response to early and late spring fires [84,233]. The average frequency of tall dropseed on a central Oklahoma rangeland was similar (P=0.54) on plots burned in late March and unburned plots [180]. Data from the Konza prairie suggest that tall dropseed had the highest cover and frequency on sites burned annually in March and November and the lowest cover and frequency on unburned sites and those burned annually in late April (Gibson [84]). On a south-central Iowa site dominated by smooth brome (Bromus inermis), Kentucky bluegrass, and tall dropseed, tall dropseed increases in cover and frequency following April fires were significant (P<0.05) and persistent, with effects present over 3 years following the first burn treatment. See the table below for values associated with various treatments [81]. Tall dropseed was included with several perennial grasses that as a group had significantly (P<0.05) higher percent composition based on cover in unburned, winter burned, and early spring burned than in mid-spring burned areas in tallgrass prairie north of Manhattan, Kansas. These grasses comprised the smallest percentage of the vegetation on late-spring burned plots, significantly (P<0.05) less than plots burned in any other season [233]. Similarly, compared to burning in late March and late April, burning in mid-May reduced the standing crop of Sporobolus species in June on a tallgrass prairie site in Nebraska [156].

Cover/frequency (%) of tall dropseed on a site in south-central Iowa before, during, and after burning in various seasons. Different letters in the same row indicate significant differences (P<0.05) in cover; + or - indicates the direction of a significant change from preburn frequency [81].
Month of Burn
Sampling period
August 1972 (preburn) August 1973** August 1974*** August 1975 August 1976
February 2/19 11/25 20/38 21/25 23/25
April 7a/25 55b/100+ 77c/100+ 71c/100+ 87c/100+
June 48/88 15/50- 26/63* 24/56 30/50
September 27a/44 0b/6** 0b/0- *** 0b/0- 5b/13
Control 0/0 6/13 8/25 6/19 20/31
*Burning was not completed due to insufficient fuels
**First postfire growing season for all treatments except September burns; preburn for September treatments
***Second postfire growing season for all treatments except September burns; first postfire growing season for September treatments

Response of tall dropseed to differences in timing of fire is likely to vary among sites and years, and may not follow the expected trend. For example, the relative basal cover comprised of tall dropseed on moderately grazed upland range and limestone breaks sites at the Kansas Agricultural Experiment Station were similar on unburned sites and those burned in early spring, mid-spring, and late spring [152]. In an upland tallgrass prairie near Grand Forks, North Dakota, May burning resulted in an increase in tall dropseed frequency from 40% the year before burning to 100% the following August. On unburned upland sites tall dropseed declined [95].

Few data are available regarding tall dropseed's response to summer fires. Tall dropseed frequency significantly declined 2 months following June fires in south-central Iowa. See the table based on data from George and others [81] for more detail. As a group, perennial warm-season midgrasses, including tall dropseed, declined following summer fires in mesquite-grassland in Texas, although the difference was not significant in 2 of the 3 years investigated and only marginally so (P<0.06) in the 3rd [229].

Although tall dropseed has been considered vulnerable to autumn fires [37,232], data suggest variable responses. Tall dropseed declined following annual autumn burning in the Konza prairie (Towne and Kemp [232]). In south-central Iowa, tall dropseed declined before autumn burning was implemented. Despite significant tall dropseed increases on spring-burned sites, tall dropseed cover remained low and did not recover on autumn-burned sites (George and others [81]). However, tall dropseed abundance was greater on autumn-burned sites than unburned sites in the Konza prairie (Gibson [84]) and in south Texas brush ranges [28] (see below).

Winter fires generally have small and/or short-term impacts on tall dropseed. On the Konza prairie tall dropseed cover declined significantly (P<0.05) following annual fires on upland and lowland sites burned either in winter, late autumn, or mid-spring. However, tall dropseed frequency increased significantly on both lowland and upland sites burned in winter. See the data table from Towne and Kemp’s [232] study for details. On an abandoned field where tall dropseed occurred with prairie threeawn in eastern Kansas, percent basal cover of tall dropseed on 4 August 1975 was 6.7% on the unburned plots, 28.3% in the plots burned 13 December 1974, and 10% each in the plots burned 9 January, 12 February, and 5 March 1975. This was a significant (P<0.05) difference between treatments. The authors suggest that reductions in prairie threeawn seedlings that occurred with December burning resulted in increases in tall dropseed on those plots [175]. In south Texas brush ranges, tall dropseed herbage production in August of 1967 was 36 lbs/acre on control plots, 87 lbs/acre in areas burned in September of 1965, 33 lbs/acre in areas burned in December 1966, and 42 lbs/acre in areas burned in both seasons [28]. Tall dropseed occurrence was slightly higher in Texas live oak plots burned in February compared to unburned plots. For details of the site conditions and fire characteristics see this study's FEIS Research Project Summary [115]. On a south-central Iowa site dominated by smooth brome, Kentucky bluegrass, and tall dropseed, burning in February did not have a significant impact on tall dropseed cover or frequency (George and others [81]). The percentage of herbaceous perennial biomass comprised of tall dropseed declined significantly (P<0.05) from 11% to 6% following late-winter burning in mesquite/mixed-grass rangelands in north-central Texas. However, differences in the percent composition of tall dropseed on these sites were not significant a year later [227]. Five years following implementation of treatments in Blackland prairie in Texas, tall dropseed was common in all treatments, including a plot experimentally burned in February [13]. Tall dropseed was included with several perennial grasses that as a group had significantly (P<0.05) higher percent cover (see above) in unburned, winter burned, and early spring burned than in mid-spring burned areas [233].

Species composition: Tall dropseed’s response to fire may be influenced by a combination of species composition and timing of fire. For example, spring fires in grasslands at a time when warm-season species are dormant and cool-season species are growing is generally thought to reduce the competitive ability of cool-season grasses compared to warm-season grasses [18,109,148,199,237]. According to a review of tallgrass prairie ecology, frequent spring fires result in increased dominance of warm-season, C4 grasses while summer fires increase abundance of cool-season species [215]. Tall dropseed followed this trend on a site in south-central Iowa where it was a codominant with the nonnative, cool-season grasses smooth brome and Kentucky bluegrass. Tall dropseed cover significantly (P<0.05) increased following April fires in 2 consecutive years, and decreased on plots burned in September. Although the decrease occurred before the first September fire, tall dropseed cover and frequency remained low following 2 consecutive September fires [81] (see table for details). However, there are exceptions to this trend. For instance, an early spring fire in an Iowa pasture with only a small proportion of warm-season grasses and low amounts of relatively green fuels did not result in increases of warm-season species [193]. The ratio of C4 to C3 grasses increased after spring fires in lowland areas of a South Dakota mixed-grass prairie community, but not in upland areas [216].

Effects of fire on tall dropseed in woodland and savanna communities are mixed. In Texas live oak vegetation units burned in February, tall dropseed relative dominance and frequency were slightly greater on burned than unburned plots. Statistical comparisons were not made. See the Research Project Summary for details [115]. In a north-central Texas mesquite/mixed-grass rangeland, an increase in herbaceous species despite burning in summer and increased herbivory in burned areas was attributed to reduction of woody plants and cactus. However, warm-season midgrasses as a group did not follow this trend [229]. Tall dropseed dominance and frequency were similar in burned and control post oak vegetation [115]. Tall dropseed exhibited a short-term decline in biomass following late winter burning in mesquite-mixed grass rangelands in north-central Texas. The percentage of perennial biomass comprised of tall dropseed declined significantly (P<0.05) from 11% to 6% following winter burning. Within 1 year, differences on the 2 sites were not significant [227]. The only occurrence of tall dropseed within a ponderosa pine woodland was reported 2 years after a severe fire killed of much of the overstory vegetation [136].

Precipitation: Precipitation is likely influences tall dropseed's postfire response due to increased moisture stress after fire (review [215]). Fire reduced the mulch layer in tallgrass prairies of Nebraska [149] and soil moisture in bluestem range in Kansas [152]. Fires in prairies during periods of drought tend to be of greater severity [215]. Generally, tufted species such as tall dropseed are more susceptible to damage from fire when conditions are dry [156].

Tall dropseed generally seems to respond positively to fires during periods of adequate precipitation [18,182,229,237,256,257] and negatively to fires during dry periods or drought [149,237,257]. Two similar reviews note that tall dropseed may exhibit strong positive responses to fire when there is adequate moisture, and that fire during [257] or following [237] dry years negatively affects at least 1 variety of tall dropseed [237,257]. Rasmussen and others [182] assert that yield of tall dropseed increased following fires in wet years. In a southwestern Minnesota old field, tall dropseed cover during the summer increased from 4.2% to 11.3% following burning in the wet spring of 1984 but did not change substantially following burning in the comparatively dry spring of 1983 [18]. During a dry period, the standing crop of Sporobolus species, including tall dropseed, was 1,308 kg/ha on unburned and fertilized areas compared to 617 kg/ha on burned and fertilized areas of a tallgrass prairie site in Nebraska [149]. Tall dropseed production was 53% greater (P<0.05) on a pasture burned in March of a wet year compared to an unburned mixed-grass pasture with Ashe juniper and oaks in Texas. Tall dropseed production exhibited a smaller, but also significant (P<0.05), increase on a site in this area burned in March of a dry year (24%). This site was in a lowland that received runoff water from storms [256]. One exception to this pattern occurred on a site near Stillwater, Oklahoma, that was burned annually in March or April since 1984: Tall dropseed frequency increased during the 1988 growing season, which had below-average precipitation. However, annual precipitation was above-average during the study period as a whole [92].

Positive responses to burning and tolerance of frequent fire may be more likely in moist tallgrass prairies of the eastern Great Plains compared to drier mixed-grass and short-grass prairies of the western Great Plains. A review notes that increases in herbage yield following burning are often reported from more humid prairies such as those in Wisconsin, Illinois, Iowa, Missouri, eastern Kansas, and eastern Oklahoma, while studies in western areas of Kansas, South Dakota, and North Dakota have reported reductions in yield after burning [130]. To maintain or improve grass production, 2 similar reviews recommend longer fire-return intervals for drier areas of the Great Plains than for more mesic areas [237,257] (see Fire Management Considerations for details). The drier mixed-grass and short-grass prairie zones may also be more likely to experience reduced productivity and longer recovery times if burned during periods of drought.

Soil/topography: Sometimes tall dropseed’s response to fire differs on sites with differing soil characteristics. In tallgrass prairies of the Konza prairie, tall dropseed's frequency and cover on sites with the same fire regimes were usually similar despite differing soil type. However, on sites burned in early April at 4-year intervals, tall dropseed was more common on silty clay soils on foot slopes compared to cherty silt soils on the upper rim of slopes. The opposite trend was observed on these soil types on plots burned annually in late April [84] (see table above). On a bluestem range site in Kansas, tall dropseed comprised similar proportions of the vegetation on claypan sites with comparatively low moisture availability and on limestone breaks and upland range sites that were either unburned, burned in early spring, or burned in mid-spring. However, on sites burned in late spring tall dropseed comprised from 4.9% to 7.9% of the vegetation on claypan sites compared to 0% to 3.9% of the vegetation on limestone breaks and upland range sites [152]. Edaphic factors and management history were more influential than fire in determining plant species composition of an early-successional Oklahoma prairie [64]. Conflicting results regarding the effects of soil depth on tall dropseed response to fire have been reported. On the Konza prairie, tall dropseed stem density was generally higher on a site with shallow soil (0-415 stems/m²) in the first 3 postfire years than on a site with deep soil (5-90 stems/m²) [54]. Frequency of tall dropseed in May, June, and August was greater on sites with deep silt loam than on a site with a comparatively shallow silt loam in Saline, Kansas, following 4 burns in 6 years, the most recent the March before sampling. Phytomass was similar on the 2 sites in May and June, but in August tall dropseed phytomass on the site with deep soil was twice that on the site with comparatively shallow soil [177]:

Average phytomass (SE) and frequency of tall dropseed on sites in Saline County, Kansas with differing soil depths that had been burned 4 times in 6 years, the most recent the previous March [177]
Month
Corner Site
(comparatively shallow silt loam)
Hill Site
(deep silt loam)
Phytomass (g/m²) Frequency (%) Phytomass (g/m²) Frequency (%)

May

4.7 (3.9) 33.3 3.2 (1.5) 58.3
June 13.2 (8.0) 16.7 12.0 (4.8) 66.7
August 14.9 (9.6) 50.0 29.7 (10.2) 75.0

Limited evidence suggests fire may be more damaging to tall dropseed in lowlands than in uplands. Frequency of tall dropseed was 100% in upslope areas of the Konza prairie, 70% at the bottom of slopes, and 0% in lowlands burned annually in March [85]. In mixed-grass prairie of southern Nebraska, relative abundance of tall dropseed differed among sites following reduced grazing and 9 prescribed fires that were conducted over a 17-year period. See the table below for details [160]. In upland tallgrass prairie near Grand Forks, North Dakota, tall dropseed frequency increased from 40% the year before fire to 100% the August after a May fire, while on unburned upland sites tall dropseed declined over this period. On a lowland site in this area, tall dropseed declined from 20% to 0% after a May fire. Tall dropseed did not occur on an unburned lowland before or after fire [95]. Although rarely a codominant on annually burned plots in the Konza prairie, tall dropseed occurred as a codominant on annually burned lowlands slightly more often than on annually burned uplands [88].

Percentage of total vascular plant biomass comprised of tall dropseed in 1976 and 1992 in a mixed-prairie of southern Nebraska. Management during this 17-year period included reduced grazing intensity and 9 prescribed fires [160].
Year All sites Silty lowland Shallow, limy upland Silty Upland
1976 7.83 15.09 4.31* 7.19
1992 9.91 0.0 1.93* 15.04
*difference significant (P<0.05) between years

Fuel Condition: Moist or green fuels on a site may result in fires that are not severe enough to benefit warm-season grasses. For example, in cool-season grasslands of southern Iowa with a comparatively high proportion of green biomass, burning in March did not alter biomass of cool- or warm-season grasses, including tall dropseed. The lack of litter on this site due to overgrazing also contributed to low fire severity [193]. On a site with a high water table in southwestern Minnesota, prescribed fire in May did not stimulate warm-season species or injure cool-season species and brush. Due to the occurrence of unburned mulch, cool-season grasses remained vigorous [18].

Fire may be more severe and more likely to negatively impact tall dropseed when tufts have substantial amounts of accumulated, dry litter [45]. Dry conditions could exacerbate this risk to tufted species. Mitchell and others [156] suggest that litter accumulation in prairie dropseed tussocks contributed to the decline of Sporobolus species following late-spring burning in tallgrass prairies of eastern Nebraska.

For details regarding the fuel characteristics of tall dropseed and its associated communities and the relationship between fuel accumulation and tall dropseed's occurrence in unburned areas, see Fuels.

Interactions between fire and grazing: Recently burned areas are often selected by grazing animals [77,96]. Recently burned areas were strongly selected for grazing in spring and summer by bison in the Konza prairie [240] and northeastern Oklahoma [96]. Selection of graminiods in burned areas resulted in an increase in forbs, with native warm-season grasses regaining dominance several years after fires in northeastern Oklahoma [96] and in 2 to 3 years after fire in north-central Oklahoma [77]. No significant interaction of fire and grazing was observed in a central Oklahoma study [39].

Tall dropseed may have greater tolerance of annual burning on sites that are grazed. On the Konza prairie, tall dropseed percent cover declined significantly (P<0.01) from 1995 to 2004 on an annually burned site that was not grazed, while declines in percent cover on annually burned sites that were grazed by bison or cattle were not significant [231]. In another Konza prairie study, tall dropseed cover on annually burned sites that were grazed was 4.5% compared to 0.38% in annually burned sites along the edge of bison wallows. On grazed sites with a 4-year fire-return interval, cover was 3.75%, while cover on the edge of bison wallows was 4.13%. These differences were not significant [234]. Tall dropseed cover on annually burned uplands grazed by bison was 15.3%, significantly (P<0.01) more than the 6.4% cover in ungrazed, annually burned areas of the Konza prairie. Occurrence of grazing had little impact on tall dropseed cover in areas burned every 4 years, with grazed areas having 8.7% tall dropseed cover and ungrazed areas having 8.1% cover [100]. However, in central Oklahoma, burning in mid-April had greater impacts on cover of tall dropseed than grazing (see Annual burning), and grazed-and-burned plots had only slightly higher cover of tall dropseed than burn-only plots [39]. On 12 mixed-grass and tallgrass prairie plots in Plymouth County, Iowa, tall dropseed occurred on 4 of 192 grazed-only quadrats and none of the quadrats that were grazed and burned 1 to 3 times in 8 years [34].

Tall dropseed may respond negatively to overgrazing in areas protected from fire. In an Ashe juniper community in Texas, tall dropseed was less abundant on "overgrazed" sites than "properly grazed" sites and less abundant on unburned sites than sites that had been burned 4 years previously. Tall dropseed comprised 21.4% of the herbaceous cover of a properly grazed site burned 4 years previously. On an overgrazed site burned 4 years previously tall dropseed comprised 5.3% of the herbaceous cover. Tall dropseed comprised 13.7% of the herbaceous cover on a properly grazed range site burned 17 years previously and was absent on an overgrazed range site burned 43 years previously [113]. According to a description of the cross timbers community type in Texas, woody species are promoted by overgrazing and fire suppression (see Fire Regimes); the rate of encroachment into open areas, where tall dropseed is likely to occur, is much faster in overgrazed areas [209]. Overgrazing may be especially damaging on sites burned during periods of drought. Declines in desirable species were long-lasting on a grazed site in the Kansas Flint Hills burned during spring drought [152].

Interactions with other management activities: Management history or concurrent management efforts in an area are likely to influence how tall dropseed responds to fire. For instance, declines in tall dropseed following burning in spring, summer, or fall on a tallgrass prairie site near Omaha, Nebraska, may have been influenced by the cessation of a 20-year mowing regime as well as a response to fire [30]. Tall dropseed comprised an average of 2% of the biomass of vegetation on unburned sites, and 5% of the biomass of burned sites in a study of the impact of various mechanical treatments and fire in a honey mesquite community of south Texas. This difference was considered significant (P<0.05). The increases in tall dropseed were greater on sites that had been burned following shredding, chopping, or scalping than on sites where these treatments occurred without burning [27]. On tallgrass prairie plots in Nebraska, occurrence of tall dropseed was lower on burned and fertilized plots than on unburned and fertilized plots [149]. On a central Oklahoma site grazed by sheep, burned and fertilized plots had lower occurrence of tall dropseed than plots that were unburned and fertilized or those that were burned and not fertilized [180]. Species composition of an early-successional tallgrass prairie in Oklahoma was more strongly influenced by land use history and edaphic factors than by fire disturbance [64].

FUELS AND FIRE REGIMES:

Fuels: Fuel loads in communities with tall dropseed vary among years, sites, and fire regimes. The maximum aboveground biomass of 3x3-foot (1x1 m) monocultures of tall dropseed in the Blackland Prairie region of central Texas was over 1,000 g/m² in 2001 and over 500 g/m² in 2002 [255]. Fine fuels in tallgrass prairies are continuous and can occur at loads of 3,000 to 4,000 lb/acre (Owensby personal communication cited by [237]). On a remnant mixed-grass prairie near Hays, Kansas, mulch depth in communities dominated by buffalograss, sideoats grama, and tall dropseed ranged from 0.9 inch (2.2 cm) in October to 1.8 inches (4.5 cm) in July [73]. Litter mass in tallgrass prairie sites with 4-foot (1.2 m) deep loamy soils in south-central Oklahoma ranged from nearly 3,000 to nearly 8,000 kg/ha on unburned sites and ranged from 0 to just over 4,000 kg/ha on sites burned 1 to 3 times. On sites with 2- to 10-inch (5-25 cm) deep loam soils over hard limestone, differences in litter mass on burned (0-4,000 kg/ha) and unburned sites (2,000-4,000 kg/ha) were less distinct, with yearly and treatment effects having a larger impact than burning [64]. Conversions of these fuel densities to kg/ha are provided in the table below for comparison:

Amount of fuel in tallgrass prairies converted to kg/ha for comparison
Location Relative abundance of tall dropseed Fuel description kg/ha
Tallgrass prairie General, not site specific Fine fuels 3,360 - 4,450 (review by [237])
Bluestem rangeland, Kansas 0.0 to 3.7% relative cover Protective mulch (dry matter) 1,220-3,240 [152]
Tallgrass prairie, south-central Oklahoma Late successional species on the site, abundance not provided Litter mass 2,000-8,000 [64]
Blackland prairie, Texas 3x3-foot (1x1 m) planted monocultures Aboveground biomass 5,000-10,000 [255]

Leaf area ratio and persistence of tall dropseed leaves may influence overall fuel characteristics. Tall dropseed leaves collected from a dune site near Ft. Supply, Oklahoma, had an average biomass of 0.9 g, average leaf area of 8,500 mm², and a leaf area ratio of 9,390 mm²/g [252]. Some leaves within dense tall dropseed bunches may remain green through winter [144,224]. Some leaves may bleach white in the winter [246] and remain on the bleached stems through a 2nd summer [246] or up to a year [188]. Tall dropseed tufts can contain substantial amounts remnant plant material [45]. See Fuel condition for potential impacts of these characteristics on tall dropseed's response to fire.

Tall dropseed may be able to tolerate longer periods without fire in communities in which fuel accumulation occurs comparatively slowly. Tall dropseed occurred at 0.2% basal cover in a shortgrass prairie dominated by buffalograss, blue grama, and western wheatgrass near Hayes, Kansas, that had not been burned or grazed by livestock for 60 years [111]. Midgrasses including tall dropseed occurred on a mixed-grass prairie that had been undisturbed for 15 years but accumulated less mulch than a neighboring undisturbed tallgrass prairie where a 4.5- to 8-inch (11-20 cm) thick mulch layer had developed and tall dropseed did not occur [250]. In the first few years following fire, tall dropseed stem density in the Konza prairie was positively correlated with weight of standing dead herbaceous material on a site with deep soil (P=0.043), but not on a site with shallow soil [54].

Fire regimes: Presettlement fire regimes in communities where tall dropseed typically occurs are characterized by frequent to occasional surface fires. A review of the tallgrass prairie ecosystem notes that fire-return intervals likely varied greatly, although typical estimates range from 2 to 5 years. Fragmentation of prairies and fire exclusion following European settlement resulted in decreases in fire frequency [215]. In a review, Wright and Bailey [257] note the role of topography: Areas of the Great Plains with level to rolling topography may experience more frequent fire, at about 5- to 10-year intervals, and those in areas with rough topography may experience fire at 15- to 30-year intervals. Large fires were most likely to occur when a period of drought followed a period of above-average precipitation, because these conditions would result in abundant, continuous, and dry fuels [257]. Analysis of burn scars in a cross timbers community with tall dropseed in the Trinity River watershed in Texas found that 16% of the area had not been burned for ≥10 years, 37% of the area had not been burned for 6 to 9 years, 44% had not been burned for 1 to 5 years, and 3% had been burned the preceding year [60]. Tall dropseed occurred on 4 of 18 plots in an Arkansas savanna-glade-woodland that had a 5.7-year fire-return interval [118]. Tall dropseed occurs in west gulf coast plain calcareous prairies in a matrix of calcareous forests in west-central Louisiana. Fire frequency in these prairies is estimated to range from 5 to 20 years [162]. Prescribed burning has increasingly been used to maintain prairie openings of the Mississippi gulf coast plain that are occupied by tall dropseed, with prescribed fire frequency on Forest Service lands in the area increasing from none in the 1960s to an average of 2.9 per prairie per decade in the 1990s. The authors believed this level of burning would maintain prairie openings [253]. See the Fire Regime Table for additional information on fire regimes of vegetation communities in which tall dropseed is likely to occur.

In prairies where tall dropseed occurs, natural, lightning-ignited fires typically occur in the growing season while many prescribed fires are conducted in the dormant season [29]. In tallgrass prairies, lightning-ignited fires occurred from March to November but were most common in the mid- to late summer [29]. According to a review, green matter and humidity may have limited the extent of such fires except in periods of drought [215]. April burns likely comprised less than 1% of lightning fires in the northern Great Plains. Burning in the dormant season, a common management practice, likely favors warm-season species more than lightning-ignited fires. Dormant-season fires along with grazing, fragmentation, and fire suppression reduce the likelihood and spread of lightning-ignited summer fires [109].

Fire exclusion may cause encroachment of woody species into communities occupied by tall dropseed. Fire is often used to restrict woody species to riparian zones and protected areas of southern mixed-grass prairie and tallgrass prairie (reviews [215,237]). Comparison of photographs from 1936 to those from the late 1970s, a period of fire exclusion, showed a decline in the area of prairie openings in the Mississippi coastal plains, a community occupied by tall dropseed [253]. In west-central Louisiana tall dropseed was listed as a species of 2 southern calcareous prairie types. In both these types physiognomy is altered by the invasion of eastern redcedar, white ash (Fraxinus americana), and honey-locust (Gleditsia triacanthos) that occurs with fire exclusion [162]. Tall dropseed was listed as a species of limestone glades of the Midwest, which depend on fire or other management to prevent succession to forest [16]. Following 8 years without burning or mowing, a northeastern Texas prairie with scattered patches of tall dropseed was developing into a "semi-woodland" due to encroachment from creek plum (Prunus rivularis) [171]. According to a review focused primarily on composite dropseed, shading associated with establishment of woody species due to fire exclusion threatens shade-intolerant species, including tall dropseed [65]. Overgrazing may result in faster rates of woody invasion than fire exclusion alone [209].

FIRE MANAGEMENT CONSIDERATIONS:
In general, periodic fires are likely to benefit tall dropseed by reducing encroachment of woody species (see above) and consuming litter layers that may inhibit tall dropseed seedling establishment (see Soil and Fuels). Tall dropseed may occur in unburned communities where little to no litter accumulates (see Fuels).

Although many interacting factors influence tall dropseed's response to fire, positive impacts may be more likely following early spring burning while negative impacts may be more likely with increasing fire frequency and after fires in dry years and/or areas. Soil characteristics have not shown any distinct association with fire response (see Soil/topography for details). Although grasses generally have recovery times of more than 2 years in burned and grazed areas [77,96], grazing in burned areas may increase tall dropseed's tolerance of annual burns [231,234]. See Interactions between fire and grazing for more information on the response of tall dropseed on burned and grazed sites and Grazing for information related to the response of tall dropseed to grazing alone.

Based on the influence of moisture on fire behavior and postfire response, many recommendations regarding prescribed fire in these communities focus not only on fire frequency but also on appropriate climate and weather conditions for burning. A 1993 BLM review suggests fire-return intervals of 5 to 10 years for the western and central Great Plains, and intervals as short as 1 to 3 years in the eastern Great Plains [237]. Wright and Bailey [257] recommend fire frequencies of 5 to 8 years in the 20-inch (50 cm) precipitation zone and suggest that fire can occur as frequently as every 1 to 3 years in the 35- to 40-inch (90-100 cm) precipitation zone. These reviews also suggest ideal conditions for burning to reduce woody materials and to reduce the risk of firebrands starting spot fires in the Great Plains, including relative humidity around 30%, temperature of about 70 to 75 °F (21-24 °C), and wind speed of just over 8 mph [237,257]. Burning when relative humidity is below 25% or temperatures are above 80 °F (27 °C) is not recommended. Variations to these recommendations based on community type are provided by Wright and Bailey [257]. Recommendations for burning to benefit tallgrass vegetation in southwestern Minnesota where tall dropseed occurred in an old field community included burning when the soil is moist, relative humidity is from 20% to 60%, wind speeds are from 5 to 15 mph, and air temperature is 60 to 75 °F (16-24 °C). Based on results of previous studies in prairie communities, Becker and others [18] also recommend against burning when the topsoil and subsoil are dry, because spring burning could be harmful if dry conditions persist. Burning when mulch is saturated is also not recommended, as low fire severity and little removal of mulch minimize the benefits of burning [18].

Other recommendations for burning in tall dropseed communities focus on minimizing the risk of erosion. Steinauer and Collins [215] note in a review that fire temporarily increases the potential for erosion. Recommendations for minimizing erosion on sites with sandy soil or slopes over 20% include burning at low severity and leaving some areas unburned [237].


MANAGEMENT CONSIDERATIONS

SPECIES: Sporobolus compositus

FEDERAL LEGAL STATUS:
None

OTHER STATUS:
A review and survey published in 2004 [65] and data from herbaria and natural heritage programs published in 2006 [68] suggest that tall dropseed in New England is rare and threatened by further development and fragmentation. As of 2004, it was at risk of becoming extirpated in Idaho [117]. Information on state- and province-level protection status of plants in the United States and Canada is available at NatureServe.

IMPORTANCE TO WILDLIFE AND LIVESTOCK:
Tall dropseed provides forage of intermediate value and typically of fair palatability for livestock. Tall dropseed may be an important component of the diet of bison [41,240], birds [99,143,166], and small mammals [124], including cottontail rabbits [176]. Tall dropseed comprised 12.5% to 25.9% of the diet of bison on the Konza prairie. Use of tall dropseed by bison [41], scaled quail, and northern bobwhite was greatest in winter. Use by scaled quail [143] and northern bobwhite [99,143] has been shown to vary with plant community [99] and occurrence of fire [77,96,143,240] (See Interactions between fire and grazing). Tall dropseed has been described as having poor forage value for wildlife [224], particularly deer [236], and was used little by grasshoppers in tallgrass pastures near Manhattan, Kansas [129]. Tall dropseed has low values of many important nutrients, which may vary with season and site factors. However, Crawford and others [44] and Johnson and Nichols [120] describe tall dropseed's forage value as fair to good.

Palatability: Palatability of tall dropseed is generally fair [166,222,224] or moderate [44]. It is most palatable early in the growing season [44,156,224] and before reaching maturity [44,224]. It was considered a "secondary forage species" for cattle, sheep, and goats [236]. In the western cross timbers of Texas it was moderately grazed in mid-March, April, and December and lightly grazed in early March, late August, and September [60]. However, it was not selected on sites in eastern Texas [127] or southeastern Nebraska [156]. Palatability may vary among tall dropseed varieties [60,144].

Nutritional content: Tall dropseed provides a fair to good source of some nutrients, while lacking others. Protein has been shown to comprise about 4% to nearly 13% of tall dropseed vegetation [24,76,114,176], while tall dropseed seeds and hulls contained 25.11% protein in a Pinchot's juniper-dominated rangeland in northwestern Texas [143]. Tall dropseed vegetation in northwestern Texas with average protein content of 6.08% was considered a deficient to fair source of protein [76]. Tall dropseed digestibility in tallgrass prairie southwest of Stillwater, Oklahoma, ranged from 38.5% to 68.7% [24], and percentage of digestible organic matter averaged 48% in tall dropseed on the Edwards Plateau in Texas [114]. Water content of tall dropseed ranged from 31% to 66% near Stillwater, Oklahoma [24], and averaged 55% in tall dropseed from the Edwards Plateau. Phosphorus comprised 0.16% of tall dropseed from the Edward Plateau [114], and percent phosphoric acid ranged from 0.12% to 0.26% in tall dropseed from northwestern Texas. Tall dropseed from this area was considered deficient to very deficient in phosphoric acid but a fair to good source of calcium oxide [76]. Fat comprised 1.9% of the dry weight of tall dropseed in an upland hardwood forest-tallgrass prairie of central Oklahoma [176]. Lipid content of tall dropseed seeds and hulls averaged 3.7% [143].

Season and site factors may influence tall dropseed nutritional value. Tall dropseed exhibited greater protein content [24,176], digestibility, and water content early in the growing season than later in the growing season [24]. Vegetation on 4-year-old and 8-year-old burn sites in Pinchot's juniper-dominated rangelands with tall dropseed provided better quality scale quail and northern bobwhite diets than unburned areas [143]. Crude protein, water content, and digestibility were generally greater in burned and herbicide treated areas of Oklahoma tallgrass prairie with tall dropseed than untreated areas [24]. In an upland forest-tallgrass prairie of central Oklahoma, tall dropseed in undisturbed areas had higher content of certain amino acids than areas subject to removal of woody species using herbicides and burning [176].

Cover value: Tall dropseed may provide cover for small mammals and ground nesting birds. Densities of various groups of grasshoppers in a tallgrass prairie with tall dropseed are provided by Craig and others [42].

Communities with tall dropseed provide cover for some small mammals. Hispid cotton rat, deer mouse, and western harvest mouse occurred at densities greater than 4.0 individuals/acre in at least one season in a buffalograss-sideoats grama-tall dropseed community near Hays, Kansas. Prairie voles selected areas of this community with dense cover [73]. In 1966 these same species occurred at densities above 2.0 individuals/trapline in a mixed-grass prairie in north-central Kansas where tall dropseed was common [125]. In a mixed-grass prairie of Ellis County, Kansas, hispid cotton rats were trapped more often than expected in all seasons based on trapping effort in vegetation dominated by buffalograss, sideoats grama, and tall dropseed and in winter and spring on another site dominated by the same species [74]. In this area, deer mouse and western harvest mouse were not significantly associated with tall dropseed in remnant prairie [221].

Ground-nesting birds that use prairies with tall dropseed include prairie chickens and quail. Tall dropseed was a dominant species in 2 communities used by greater prairie chickens in Kansas, one that was preferred in all seasons and another that was preferred in summer [190]. Greater prairie chickens used tallgrass prairies with a small component of tall dropseed more than mid- and shortgrass prairies with substantial proportions of tall dropseed. Lesser prairie chickens used limited areas of the shortgrass prairies [122]. Increases in tall dropseed where it is scarce could potentially improve the quality of quail habitat in western Oklahoma. Tall dropseed generally has fair value for nesting habitat and low value for protective cover [166].

VALUE FOR REHABILITATION OF DISTURBED SITES:
Tall dropseed may have potential for preventing erosion [23,63,65] and for use in prairie restoration [178,198]. Fell [69] lists tall dropseed as a species that stabilizes sandy soils in northern Illinois. Tall dropseed survival in restoration plantings on a museum site in Kansas was 86% to 94% in the 2 years after planting. Tall dropseed individuals flowered their 1st year [178]. In the restoration of a dump site in Texas, transplanted tall dropseed showed high survival, and plants sown from seeds had moderate growth rates [243]. In northeastern Kansas, tall dropseed was present in about 70% of Conservation Reserve Program plots that were seeded with warm-season native species [119]. However, tall dropseed did not persist over the long term on a Wisconsin prairie restoration site, despite good germination at the beginning of the project [212]; and tall dropseed was not observed in the 3 years after seeding at a rate of 10 seeds/m² on a lowland agricultural field in the Konza prairie [10].

OTHER USES:
No information is available on this topic.

OTHER MANAGEMENT CONSIDERATIONS:
Most information suggests that tall dropseed increases in the short term with moderate or heavy grazing. Mowing, soil disturbance by animals such as badgers, and control of weeds may also benefit tall dropseed.

Grazing: Tall dropseed may indicate fair to good quality range. Tall dropseed was absent from a poor range site in the western Cross Timbers [60] and comprised a small percentage of production on a poor range site in a Texas limestone prairie [186]. It may reach maximum production on range sites in fair and good condition [60,186]. Increasing abundance of tall dropseed has been asserted as an indicator of improving range condition [27,92]. See Renner and Allred [186] and Weaver [247] for tall dropseed occurrence, and Dyksterhuis [60] for tall dropseed absence from range sites classified in excellent condition.

Tall dropseed typically increases or is not significantly impacted by cattle or bison grazing in tallgrass prairie. On annually burned sites in Konza Prairie, frequency of tall dropseed increased from 63.8% in 1995 to 87.5% in 2004 on sites grazed by bison, and increased from 75% in 1995 to 97% in 2004 on sites grazed by cattle (P<0.05). Frequency on the annually burned and ungrazed site did not change significantly from 1995 to 2004. Cover of tall dropseed declined on all sites from 1995 to 2004, but this reduction was only significant on the ungrazed sites [231]. Tall dropseed cover on annually burned sites in Konza prairie was 15.3% in upland areas grazed by bison, significantly greater than the 6.4% cover in upland areas that were not grazed. However, on upland sites burned every 4 years, the difference in tall dropseed cover between sites grazed by bison (8.7%) and sites that were not grazed (8.1%) were not significant [100]. See Interactions between fire and grazing for more details regarding impacts of various combinations of grazing and burning treatments. In sandhill mixed-grass prairie pastures in northwestern Oklahoma, tall dropseed frequency was 0.8% in areas where cattle were excluded for 50 years, significantly (P=0.006) less than the 2.5% frequency in plots moderately grazed by cattle year-round [204]. On tallgrass prairie sites on a research station in Canadian County, Oklahoma, that had been grazed by cattle for at least 15 years prior to implementation of treatments, tall dropseed cover was similar on sites undisturbed for 2 years and sites moderately to heavily grazed for 2 years [39]. Tall dropseed has been listed as a dominant on a tallgrass prairie site in Nebraska with a 25-year history of moderate summer grazing [149], and a subdominant on a site with a 10-year history of winter grazing primarily by cow-calf pairs in Kansas [174]. Tall dropseed occurred at a frequency of 8.9% on eroded sites of the Oklahoma State University Ecology Preserve near Stillwater, Oklahoma, that were highly overgrazed or used as salting areas [137].

While it is often asserted that tall dropseed increases following grazing [7,18,101,130,141,205], Weaver [248] categorized tall dropseed as a decreaser in tallgrass prairies, Johnson and Nichols [120] report that tall dropseed decreases with increasing grazing pressure in a summary of South Dakota range species, Andelt and others [6] included tall dropseed in a group of species that increased with reduced grazing in south Texas chaparral and savanna/mixed-grass communities, and tall dropseed was considered a decreaser on a South Dakota, mixed-grass prairie range site with clay loam to heavy clay soils [145]. Crawford and others [44] categorized tall dropseed as a species that declined with grazing in the southern and western portions of the Ozarks, but suggested it likely increased with grazing in the northern and eastern portions of the Ozarks. Several factors may explain the variation in responses of tall dropseed to grazing, including moisture availability and intensity and/or season of grazing. Variety of tall dropseed may also influence grazing response. A review within a New England conservation and research plan notes that composite dropseed generally increases with grazing [65].

Moisture availability may influence tall dropseed's response to grazing. As a group, grasses are typically more vulnerable to grazing during periods of drought (review [215]). In tallgrass prairie near Stillwater, Oklahoma, frequency of many grasses, likely including tall dropseed, did not differ between grazed and ungrazed pastures during a 5-year period of above-average precipitation [92]. In mesquite/midgrass rangeland of north-central Texas, C4 midgrasses declined on both continuously and rotationally grazed plots during a 4-year drought [228]. Stubbendieck and others suggest that tall dropseed declines under heavy grazing pressure on dry sites and increases on more mesic sites [222]. Seventeen years following implementation of regular burning and substantially decreased grazing on a previously continuously grazed mixed-grass prairie pasture in southern Nebraska, tall dropseed doubled on a silty upland site and declined on a silty lowland site and on a hillside with shallow, limy soil. Only the decline on the limy hillside site was significant (P<0.05) [160].

As of late 2009, tall dropseed's response to differences in intensity of grazing is unclear. Several sources suggest that tall dropseed increases under moderate or short-term heavy grazing but declines with prolonged heavy grazing [101,152,209,236]. Tall dropseed followed this trend in an Ashe juniper community in Texas [113] and a mesquite/mixed-grass community in southeastern Texas [169]. In mesquite-midgrass rangeland of north-central Texas, perennial herbaceous basal area, which includes tall dropseed, was greater (P<0.05) under rotational grazing during periods of adequate precipitation and exhibited decreased rates of decline during a period of drought compared to continuous grazing [228]. Midgrasses including tall dropseed on a range site near Stillwater, Oklahoma, were not influenced by grazing system but decreased with increasing stocking rates [91]. Stocking rates and grazing schedules did not have significant impacts on groups of grasses that included tall dropseed in a tallgrass prairie in the same area during a period of above-average precipitation [92] or in mixed-grass prairie near Clinton, Oklahoma [90]. In rangeland comprised of warm-season grasses, tall dropseed was common on both year-round and intermittently grazed areas [119]. In contrast, others have found tall dropseed more abundant on more frequently or more heavily grazed areas than those grazed at lower intensities ([227], Hazel 1967 cited in [188]). Stubbendieck and others [224] note tall dropseed increases under "excessive" grazing. McCollum and others [151] and Powell and others [180] provide additional information on the effects of grazing on graminiod communities with tall dropseed in Oklahoma.

Tall dropseed's response to season of grazing is also uncertain. Leithead and others [144] suggest tall dropseed may decline on sites grazed in the winter and increase on those grazed in summer. However, tall dropseed was apparently restricted to winter-to-spring grazed areas of a lowland site in the Edwards Plateau in Texas. The trend on upslope and plateau sites in this area was less clear [153].

Other disturbance: Tall dropseed may increase following mowing. Tall dropseed increased slightly following mowing a pasture on the Edwards Plateau in Texas. Tall dropseed may increase or tolerate mowing in autumn, spring [84], and summer [84,119]. Tall dropseed increased significantly (P<0.03) from 1998 to 2001 on restoration plots where herbicide and seed had been applied in 1994 and annual mowing began in fall of 1995 [75]. On the Konza prairie, tall dropseed was an indicator of communities on some soils that were unburned and mowed in November [87]. However, mowing in July [84] and August [37] has resulted in tall dropseed declines.

Data from the Konza prairie suggest that tall dropseed may benefit from animal disturbance of soil. Tall dropseed had greater cover on badger dens than undisturbed prairies (P<0.05) [83]. In contrast, cover of tall dropseed in June was significantly (P<0.05) greater on sites grazed by bison than at the edges of bison wallows [234].

Differing land uses may impact occurrence of tall dropseed. High use by off-road traffic was associated with reduced cover of tall dropseed at the Fort Wiley Military Reservation in northeast Kansas [181]. However, tall dropseed frequency was similar to expected in roadsides adjacent to croplands, hayfields, pastures and woodlands in southeastern Iowa [26].

Weeds and herbicides: Control of invasive herbs may benefit tall dropseed. Tall dropseed did not occur in tallgrass prairie openings of southern Kansas where nonnative, invasive sericea lespedeza (Lespedeza cuneata) had established, but did occur in openings were lespedeza did not occur [61]. In a tallgrass prairie where tall dropseed was one of several dominants, grass biomass was weakly negatively associated with lespedeza biomass [46]. Use of herbicides to control nonnative cool-season grasses resulted in a significant (P≤0.1) short-term increase in tall dropseed biomass on a site in southern Iowa [193]. Tall dropseed "responded well" to burning and herbicide application to control tall fescue (Schedonorus arundinaceus) on a south-central Kentucky restoration site [245] and tolerated spring herbicide application during attempts to control tall fescue and other nonnative cool-season grasses on 14 remnant grasslands in Kentucky [12]. However, frequency of tall dropseed showed a statistically insiginficant decline on a pasture in the Edwards Plateau following herbicide application to control yellow bluestem (Bothriochloa ischaemum) [202].


APPENDIX: FIRE REGIME TABLE

SPECIES: Sporobolus compositus
The following table provides fire regime information that may be relevant to tall dropseed habitats. Due to a lack of information regarding community composition of areas occupied by tall dropseed in the western United States, New England, and Atlantic coastal states lists for these areas are incomplete or excluded. The following list focuses on those communities where tall dropseed is most likely to occur. Follow the links in the table to documents that provide more detailed information on these fire regimes.

Fire regime information on vegetation communities in which tall dropseed is likely to occur. This information is taken from the LANDFIRE Rapid Assessment Vegetation Models [139], which were developed by local experts using available literature, local data, and/or expert opinion. This table summarizes fire regime characteristics for each plant community listed. The PDF file linked from each plant community name describes the model and synthesizes the knowledge available on vegetation composition, structure, and dynamics in that community. Cells are blank where information is not available in the Rapid Assessment Vegetation Model.
Great Basin Northern and Central Rockies Northern Great Plains Great Lakes
Northeast South-central US Southern Appalachians Southeast
Great Basin
Vegetation Community (Potential Natural Vegetation Group) Fire severity* Fire regime characteristics
Percent of fires Mean interval
(years)
Minimum interval
(years)
Maximum interval
(years)
Great Basin Grassland
Great Basin grassland Replacement 33% 75 40 110
Mixed 67% 37 20 54
Northern and Central Rockies
Vegetation Community (Potential Natural Vegetation Group) Fire severity* Fire regime characteristics
Percent of fires Mean interval
(years)
Minimum interval
(years)
Maximum interval
(years)
Northern and Central Rockies Grassland
Northern prairie grassland Replacement 55% 22 2 40
Mixed 45% 27 10 50
Northern Great Plains
Vegetation Community (Potential Natural Vegetation Group) Fire severity* Fire regime characteristics
Percent of fires Mean interval
(years)
Minimum interval
(years)
Maximum interval
(years)
Northern Plains Grassland
Nebraska Sandhills prairie Replacement 58% 11 2 20
Mixed 32% 20    
Surface or low 10% 67    
Northern mixed-grass prairie Replacement 67% 15 8 25
Mixed 33% 30 15 35
Southern mixed-grass prairie Replacement 100% 9 1 10
Central tallgrass prairie Replacement 75% 5 3 5
Mixed 11% 34 1 100
Surface or low 13% 28 1 50
Northern tallgrass prairie Replacement 90% 6.5 1 25
Mixed 9% 63    
Surface or low 2% 303    
Southern tallgrass prairie (East) Replacement 96% 4 1 10
Mixed 1% 277    
Surface or low 3% 135    
Oak savanna Replacement 7% 44    
Mixed 17% 18    
Surface or low 76% 4    
Great Lakes
Vegetation Community (Potential Natural Vegetation Group) Fire severity* Fire regime characteristics
Percent of fires Mean interval
(years)
Minimum interval
(years)
Maximum interval
(years)
Great Lakes Grassland
Mosaic of bluestem prairie and oak-hickory Replacement 79% 5 1 8
Mixed 2% 260    
Surface or low 20% 2   33
Great Lakes Woodland
Northern oak savanna Replacement 4% 110 50 500
Mixed 9% 50 15 150
Surface or low 87% 5 1 20
Northeast
Vegetation Community (Potential Natural Vegetation Group) Fire severity* Fire regime characteristics
Percent of fires Mean interval
(years)
Minimum interval
(years)
Maximum interval
(years)
Northeast Woodland
Eastern woodland mosaic Replacement 2% 200 100 300
Mixed 9% 40 20 60
Surface or low 89% 4 1 7
South-central US
Vegetation Community (Potential Natural Vegetation Group) Fire severity* Fire regime characteristics
Percent of fires Mean interval
(years)
Minimum interval
(years)
Maximum interval
(years)
South-central US Grassland
Bluestem-sacahuista Replacement 70% 3.6 1  
Mixed 30% 7.7 2  
Blackland prairie Replacement 96% 4    
Surface or low 4% 100    
Southern shortgrass or mixed-grass prairie Replacement 100% 8 1 10
Southern tallgrass prairie Replacement 91% 5    
Mixed 9% 50    
Oak savanna Replacement 3% 100 5 110
Mixed 5% 60 5 250
Surface or low 93% 3 1 4
South-central US Woodland
Mesquite savanna Replacement 5% 100    
Mixed 4% 150    
Surface or low 91% 6    
Oak-hickory savanna (East Texas) Replacement 1% 227    
Surface or low 99% 3.2    
Interior Highlands dry oak/bluestem woodland and glade Replacement 16% 25 10 100
Mixed 4% 100 10  
Surface or low 80% 5 2 7
Oak woodland-shrubland-grassland mosaic Replacement 11% 50    
Mixed 56% 10    
Surface or low 33% 17    
South-central US Forested
Cross Timbers Replacement 3% 170    
Mixed 2% 250    
Surface or low 94% 6    
Southern Appalachians
Vegetation Community (Potential Natural Vegetation Group) Fire severity* Fire regime characteristics
Percent of fires Mean interval
(years)
Minimum interval
(years)
Maximum interval
(years)
Southern Appalachians Grassland
Bluestem-oak barrens Replacement 46% 15    
Mixed 10% 69    
Surface or low 44% 16    
Eastern prairie-woodland mosaic Replacement 50% 10    
Mixed 1% 900    
Surface or low 50% 10    
Southeast
Vegetation Community (Potential Natural Vegetation Group) Fire severity* Fire regime characteristics
Percent of fires Mean interval
(years)
Minimum interval
(years)
Maximum interval
(years)
Southeast Grassland
Southeast Gulf Coastal Plain Blackland prairie and woodland Replacement 22% 7    
Mixed 78% 2.2    
Southeast Shrubland
Pocosin Replacement 1% >1,000 30 >1,000
Mixed 99% 12 3 20
Southeast Woodland
Longleaf pine-Sandhills prairie Replacement 3% 130 25 500
Surface or low 97% 4 1 10
*Fire Severities—
Replacement: Any fire that causes greater than 75% top removal of a vegetation-fuel type, resulting in general replacement of existing vegetation; may or may not cause a lethal effect on the plants.
Mixed: Any fire burning more than 5% of an area that does not qualify as a replacement, surface, or low-severity fire; includes mosaic and other fires that are intermediate in effects.
Surface or low: Any fire that causes less than 25% upper layer replacement and/or removal in a vegetation-fuel class but burns 5% or more of the area [97,138].

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