Index of Species Information

SPECIES:  Digitaria californica


SPECIES: Digitaria californica
AUTHORSHIP AND CITATION : Walsh, Roberta A. 1993. Digitaria californica. In: Fire Effects Information System, [Online]. U.S. Department of Agriculture, Forest Service, Rocky Mountain Research Station, Fire Sciences Laboratory (Producer). Available: [].

ABBREVIATION : DIGCAL SYNONYMS : Trichachne californica (Benth.) Chase [15,23,38] SCS PLANT CODE : DICA8 TRCA2 COMMON NAMES : Arizona cottontop cottontop cotton-top Arizona cottongrass cotton grass California cottontop TAXONOMY : The currently accepted scientific name of Arizona cottontop is Digitaria californica (Benth.) Henrard [15,23,38]. It is a member of the tribe Paniceae in the grass family (Poaceae) [15]. There are no recognized subspecies, varieties, or forms. LIFE FORM : Graminoid FEDERAL LEGAL STATUS : No special status OTHER STATUS : NO-ENTRY


SPECIES: Digitaria californica
GENERAL DISTRIBUTION : Arizona cottontop is distributed from the southwestern United States to central Mexico [8,15,24]. It is also found in Baja California and is reported from South America [19]. ECOSYSTEMS : FRES30 Desert shrub FRES31 Shinnery FRES32 Texas savanna FRES33 Southwestern shrubsteppe FRES34 Chaparral - mountain shrub FRES35 Pinyon - juniper FRES38 Plains grasslands FRES40 Desert grasslands STATES : AZ CA CO HI NV NM OK TX MEXICO BLM PHYSIOGRAPHIC REGIONS : 7 Lower Basin and Range 11 Southern Rocky Mountains 12 Colorado Plateau 13 Rocky Mountain Piedmont 14 Great Plains KUCHLER PLANT ASSOCIATIONS : K023 Juniper - pinyon woodland K027 Mesquite bosque K031 Oak - juniper woodlands K039 Blackbrush K040 Saltbush - greasewood K041 Creosotebush K042 Creosotebush - bursage K043 Paloverde - cactus shrub K044 Creosotebush - tarbush K045 Ceniza shrub K053 Grama - galleta steppe K054 Grama - tobosa prairie K057 Galleta - three-awn shrubsteppe K058 Grama - tobosa shrubsteppe K059 Trans-Pecos shrub savanna K060 Mesquite savanna K061 Mesquite - acacia savanna K065 Grama - buffalograss K071 Shinnery K085 Mesquite - buffalograss K086 Juniper - oak savanna K087 Mesquite - oak savanna SAF COVER TYPES : 66 Ashe juniper - redberry (Pinchot) juniper 67 Mohrs ("shin") oak 68 Mesquite 239 Pinyon - juniper 241 Western live oak 242 Mesquite SRM (RANGELAND) COVER TYPES : NO-ENTRY HABITAT TYPES AND PLANT COMMUNITIES : NO-ENTRY


SPECIES: Digitaria californica
IMPORTANCE TO LIVESTOCK AND WILDLIFE : Arizona cottontop responds quickly to spring and summer rains, grows rapidly, and provides highly palatable green forage. The foliage cures well, and some stems remain green in winter so that it is an important winter feed [20]. It also makes rapid growth following winter rains, and furnishes earlier forage than most associated grasses [15]. PALATABILITY : Arizona cottontop provides good graze for livestock and fair graze for wildlife [14]. Arizona cottontop was given a high palatability rating for cattle [2]. It is palatable throughout the year [14]. It is preferred by cattle over most other grass species at all seasons of the year [8]. In a study of preferential grazing of native grasses and the introduced grass species Lehmann lovegrass (Eragrostis lehmanniana) in Arizona, cattle consumption of native grasses was greater than 75 percent, versus less than 20 percent for Lehmann lovegrass. Arizona cottontop was a preferred species even among the native grasses [29]. When compared to Arizona cottontop plants outside the canopy cover, cattle grazed Arizona cottontop closely and preferentially under mesquite. This may have been due to the greater palatability of those plants because of their higher nutrient content [29]. NUTRITIONAL VALUE : NO-ENTRY COVER VALUE : NO-ENTRY VALUE FOR REHABILITATION OF DISTURBED SITES : Arizona cottontop can be successfully reseeded on upland areas receiving at least 11 inches (280 mm) of annual precipitation, provided a good seedbed has been prepared. In New Mexico, Arizona cottontop gave the best germination of all native forage plants tested, but seedlings made slower growth than most other plants. Thus, moisture had to be available for a longer period for Arizona cottontop seedlings. However, once plants are established, they are drought hardy. Populations are maintained by establishment of new plants from seed during wet years. Once established, Arizona cottontop can be quite long lived. Some plants live for more than 15 years, even when grazed [8]. In less favorable sites, reseeding efforts may not succeed. In the Sonoran and Chihuahuan deserts extreme drought, overgrazing, sheet and gully erosion, and plowing caused extreme deterioration of rangeland. Native species, including Arizona cottontop, failed to persist after reseeding efforts, and were replaced with introduced grasses, forbs, and shrubs [10]. The accumulated heat needed for Arizona cottontop seeds to germinate is on the low end for warm-season range grasses tested, and Arizona cottontop is therefore one of the easier species to establish. It is a good choice for native grass reseeding provided that the moisture requirement for seedling establishment is met [22]. OTHER USES AND VALUES : NO-ENTRY OTHER MANAGEMENT CONSIDERATIONS : Arizona cottontop tolerates relatively heavy grazing over long periods. Dormant-season grazing averaging over 65 percent use for periods up to 15 years had no apparent effect on longevity, changes in basal area, or changes in plant height [8]. In studies of productivity, cottontop succeeded about as well in dry as in wet years [28,30]. Arizona cottontop will thrive under most management strategies, provided that the intensity of grazing is held to a reasonable level [8]. Grazing, particularly at the beginning of the growing season, actually increases the sprouting and growth of axillary shoots, leading to increased productivity [9]. However, because it is highly palatable throughout the year, it is frequently overgrazed [20]. Two management practices are recommended to maintain optimum Arizona cottontop productivity [8]: 1. If Arizona cottontop is dominant, utilization should be based on 50 percent use of cottontop. If it is not the dominant grass, its use should average a little less than 60 percent. 2. Defer or reduce grazing by about 50 percent during the growing season, 2 years out of 3. This will lessen the grazing impact on Arizona cottontop, but still provide the stimulus for axillary sprouting. Under moderate grazing in Arizona, Arizona cottontop was somewhat more dense under a year-long grazing schedule than under a rotation system, but the difference was slight. These results were attributed to initial plant densities near the maximum, and to moderate grazing. On range that was initially in poor condition, rotation grazing improved cottontop productivity [28]. Consistent heavy grazing during the summer growing season adversely affects vigor and productivity of Arizona cottontop [8]. An established stand of Arizona cottontop competes strongly with velvet mesquite seedlings (Prosopis velutina) and deters the spread of velvet mesquite into grasslands. However, in a mature stand of velvet mesquite there can be great reduction of cottontop production. On many sites, removal of velvet mesquite releases Arizona cottontop, with subsequent large increases in cottontop production [8]. In Texas, when honey mesquite (P. glandulosa var. glandulosa) was removed Arizona cottontop increased most when the mesquite was cut at ground level and the stump was painted with herbicide. Arizona cottontop remained consistently above the control in its abundance with aerial spraying of honey mesquite. However, it decreased or was completely replaced when grubbing and chaining of honey mesquite induced a lower seral stage due to soil disturbance [5,21]. Rootplowing produces a highly disturbed seedbed, which reduces cottontop density and increases competition from weeds [32]. In desert soils with very poor nutrient status, Arizona cottontop can be much more productive under mesquite (Prosopis spp). However, under these conditions cattle will preferentially graze Arizona cottontop beneath the mesquite, which can result in scanty vegetational cover on these sites. A manager might then conclude that mesquite is inhibiting Arizona cottontop growth and should be eliminated, when the opposite may be true [35]. Therefore, soil nutrient status should be assessed before mesquite removal, and also before reseeding efforts. Deficiencies may need to be corrected with commercial fertilizers [25]. Removal of the crown cover of redberry juniper (Juniperus pinchoti) which had been killed by herbicide resulted in an increase in Arizona cottontop on the site. However, cottontop was only found beneath the dead junipers, and not between them [16]. In the Chihuahuan and Sonoran deserts a series of studies showed that substantial increases in native forage production, including Arizona cottontop, can be obtained if [10]: 1. Plant competition from shrubs and forbs is reduced (by mechanical means or with herbicides) 2. Dead standing litter remains in place after treatment 3. Grazing is excluded or reduced.


SPECIES: Digitaria californica
GENERAL BOTANICAL CHARACTERISTICS : Arizona cottontop is a native, perennial, long-lived, warm-season bunchgrass [8]. It has slender, erect stems which are from 12 to 40 inches (30-100 cm) tall. The leaves are normally 3 to 5 inches (8-13 cm) long, but may be up to 10 inches (25 cm) in length. They are 0.125 to 0.25 inches (2-6 mm) broad [14,20]. The inflorescence is a narrow, densely flowered panicle, usually 3 to 4.75 inches (8-12 cm) long [14]. Spikelets are normally borne in pairs on the rachis. The cottony seedhead is covered with long silky hairs [24], and the seeds are about 0.07 inches (1.7 mm) long. Arizona cottontop's root system is finely divided and branched. It is concentrated mostly in the upper 8 inches (20 cm) of soil, but in coarse-textured soils it extend down to about 40 inches (100 cm) [8]. RAUNKIAER LIFE FORM : Hemicryptophyte REGENERATION PROCESSES : Arizona cottontop reproduces from seed, and can be either self-pollinated or outcrossed. Over half of the florets of an Arizona cottontop plant are self-pollinated. The self-pollinated ovaries can mature to viable seed even if lack of soil moisture prevents the panicle from emerging from the sheath [8]. Seeds drop from the branches at maturity [20]. In a seed longevity test, Arizona cottontop seeds kept under uncontrolled conditions maintained over 80 percent germination for 3 years, with declining germination of about 6 percent per year for the next 14 years, to less than 10 percent [8]. In another study of seed in uncontrolled storage, Arizona cottontop showed 25 percent germination after 25 years [36]. Arizona cottontop reproduces vegetatively from basal buds, which sprout primarily in the spring, producing the year's crop of basal culms, most of which mature the following summer [8]. SITE CHARACTERISTICS : Arizona cottontop is found on plains and hillsides on open, well-drained sites [14,17]. Some of the diverse areas in which it occurs include mesas and rocky hills in Arizona [24], deep hardland range sites in Texas [5], and broad alluvial plains, fans, and river bottoms in the Chihuahuan and Sonoran deserts [10]. Arizona cottontop grows on a wide variety of soils, including clayey loam, sandy loam, and loose gravelly soils, as well as limestone ledges and porphyritic hills. However, it is more abundant and productive on clay, sand, or sandy-loam subsoils than on shallow, stony, or cobbly soils [8]. In the low-fertility soils of some desert sites, Arizona cottontop thrives under mesquite shrubs, where the nitrogen, sulfur, and phosphorus availability is much higher. Cottontop shows evidence of chlorosis and low fertility on some open desert sites [35]. Arizona cottontop has been recorded at the following elevations [4,5,10,14,17,27,29,40]: Area Elevation (feet) Elevation (m) Arizona 1,000-6,000 305-1,830 Chihuahuan and Sonoran deserts 0-6,050 0-1,859 Colorado 5,500-5,800 1,675-1,770 Mexico 3,940-5,250 1,200-1,600 New Mexico 4,300 1,310 Texas 1,260-3,200 384-975 Within its geographical range, Arizona cottontop grows in a wide variety of precipitation regimes, from areas of spring and summer maxima separated by dry periods in Arizona, to high-summer, low-winter types in Texas [8]. In much of its range, precipitation arrives during two periods: with winter frontal systems during November to March and with summer convection storms from June to September. However, across the region annual precipitation and time of occurrence is extremely variable, and extended drought is common. SUCCESSIONAL STATUS : Facultative Seral Species Arizona cottontop is listed as an important member of the semidesert grassland climax vegetation [8]. It is also a climax species in the shortgrass community in Texas [2], and is listed as a dominant in the mixed-prairie association in north-central Texas [5]. It is a climax decreaser, becoming less abundant where rangelands are overgrazed [11,30]. On some sites it becomes the dominant species when protected from grazing, greatly surpassing other grasses in abundance [8]. Arizona cottontop is usually found interspersed with other grasses [20], but in some wetter sites can form almost pure stands [8]. SEASONAL DEVELOPMENT : Arizona cottontop is dormant during dry periods, but utilizes both winter and summer precipitation. However, most herbage is produced during the summer growing season [8]. It responds quickly to spring and summer rains, making rapid growth [20], and also responds with rapid growth following winter rains [15]. Essentially all basal culms produced in any given year sprout during the spring growing period; summer growth on most basal culms is a continuation of growth on shoots that sprouted in spring [8]. Shoots are produced throughout the growing season. Inflorescences begin emerging 2 to 3 weeks after growth starts in the summer, and the topmost spikelets begin to fall within 5 to 8 days of full emergence. All seeds on a panicle have usually fallen within 7 to 8 days of first shatter. New panicles are produced as late in the fall as soil moisture is available [8]. Plants can set seed from July to November when conditions are favorable [14]. Germinable seed is therefore present whenever conditions are favorable for germination and establishment. Because Arizona cottontop has low-level apical dominance and a large reservoir of buds at culm nodes, numerous axillary shoots develop over the growing season. Removing the growing point at the beginning of the summer growing season stimulates the sprouting and growth of axillary shoots [8].


SPECIES: Digitaria californica
FIRE ECOLOGY OR ADAPTATIONS : Arizona cottontop is particularly tolerant of fire because the growing points are just at or below the ground line [33]. FIRE REGIMES : Find fire regime information for the plant communities in which this species may occur by entering the species name in the FEIS home page under "Find Fire Regimes". POSTFIRE REGENERATION STRATEGY : Tussock graminoid


SPECIES: Digitaria californica
IMMEDIATE FIRE EFFECT ON PLANT : Arizona cottontop is intermediate among semidesert grasses in its susceptibility to damage from fire [7]. If a wet summer follows a fire, cottontop will probably recover completely during the first growing season. If the fire is followed by a dry summer, complete recovery will probably require two summers [6,8]. DISCUSSION AND QUALIFICATION OF FIRE EFFECT : NO-ENTRY PLANT RESPONSE TO FIRE : Arizona cottontop survived a late March fire in light to moderate fuels (1,000-4,000 pounds [454-1,816 kg] per acre of fine fuel) to provide forage during a period of less than normal precipitation from May through August in western Texas [18]. After a range fire in western Texas, Arizona cottontop increased production for one to three growing seasons after fire [37]. Also in western Texas, Arizona cottontop was harmed by fire during dry years, but not during years when fire was followed by favorable moisture [7]. In Texas, hot fires with 3,037 pounds fuel per acre [3,417 kg/ha] on herbicide treated mixed brush released Arizona cottontop [39]. On an unburned site in southern Texas, low value forage species predominated; perennial bunchgrasses were scattered and of low vigor. By 3 to 5 years after a prescribed fire program, the site was dominated by Arizona cottontop and other perennial bunchgrasses [33]. Wright [41] states that in shortgrass prairie with less than 13 to 15 inches (330-380 mm) of annual precipitation, grasses do not benefit from burning, except when shrubs or litter have stagnated grass growth. In the mixed-grass prairie of the Southern Great Plains, Arizona cottontop was tolerant of fire, showing increased yield 1 year after fire when moisture was adequate. Seed production was very prolific in this species after being burned [40]. DISCUSSION AND QUALIFICATION OF PLANT RESPONSE : NO-ENTRY FIRE MANAGEMENT CONSIDERATIONS : In places where fire suppression has allowed invasion of original semidesert grassland by woody plants, burning can reduce heavy brush cover and suppress invasion. A maintenance fire should be a dormant-season, relatively cool fire initiated under high relative humidity and low wind speed. A reclamation fire should be hot, with low relative humidity and relatively high wind speed to move fire across fine fuels and into woody crowns. A first burn may not be uniform, but with the release of Arizona cottontop and other grass species, fine fuel will increase, and the second or third burn will be more uniform [33]. In southern Texas brushlands, mechanical roller chopping of brush without fire led to increased production of forbs and sedges. With burning after chopping, production shifted to predominantly perennial grasses, including Arizona cottontop [33]. In western Texas, winter-spring precipitation was the key to successful response of Arizona cottontop to fire. Species that accumulated the most litter, including Arizona cottontop, benefited the most [40].

References for species: Digitaria californica

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