SPECIES: Corylus americana
SPECIES: Corylus americana
AUTHORSHIP AND CITATION : Coladonato, Milo. 1993. Corylus americana. 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/plants/shrub/corame/all.html .
ABBREVIATION : CORAME SYNONYMS : NO-ENTRY SCS PLANT CODE : COAM COMMON NAMES : American hazelnut Americam hazel American filbert TAXONOMY : The currently accepted scientific name for American hazelnut is Corylus americana Walt. [17,31]. Two subspecific taxa based on morphological differences are found in southwestern Missouri and southeastern Kansas: C. a. var. indehiscens Palm. & Steyerm. and C. a. forma missouriensis (A. DC.) Fern. . LIFE FORM : Shrub FEDERAL LEGAL STATUS : No special status OTHER STATUS : NO-ENTRY
SPECIES: Corylus americana
DISTRIBUTION AND OCCURRENCE
GENERAL DISTRIBUTION : American hazelnut occurs from Maine west to Saskatchewan, south to eastern Oklahoma, east to Georgia, and north through New England [5,17,31]. ECOSYSTEMS : FRES10 White - red - jack pine FRES11 Spruce - fir FRES14 Oak - pine FRES15 Oak - hickory FRES17 Elm - ash - cottonwood FRES18 Maple - beech - birch FRES19 Aspen - birch STATES : AL AR GA IL IN IA KS KY LA ME MD MA MI MN MS MO NH NJ NY NC ND OH OK PA RI SC SD TN VT VA WV WI MB ON PQ SK BLM PHYSIOGRAPHIC REGIONS : 14 Great Plains KUCHLER PLANT ASSOCIATIONS : K081 Oak savanna K093 Great Lakes spruce - fir forest K095 Great Lakes pine forest K099 Maple - basswood forest K100 Oak - hickory forest K101 Elm - ash forest K103 Mixed mesophytic forest K104 Appalachian oak forest K106 Northern hardwoods K108 Northern hardwoods - spruce forest K100 Oak - hickory forest K111 Oak - hickory - pine forest K112 Southern mixed forest SAF COVER TYPES : 1 Jack pine 5 Balsam fir 12 Black spruce 13 Black spruce - tamarack 14 Northern pin oak 15 Red pine 16 Aspen 17 Pin cherry 18 Paper birch 20 White pine - northern red oak - red maple 21 Eastern white pine 22 White pine - hemlock 23 Eastern hemlock 24 Hemlock - yellow birch 25 Sugar maple - beech - yellow birch 26 Sugar maple - basswood 27 Sugar maple 30 Red spruce - yellow birch 31 Red spruce - sugar maple - beech 32 Red spruce 35 Paper birch - red spruce - balsam fir 39 Black ash - American elm - red maple 40 Post oak - blackjack oak 42 Bur oak 43 Bear oak 44 Chestnut oak 51 White pine - chestnut oak 52 White oak - black oak - northern red oak 53 White oak 55 Northern red oak 57 Yellow-poplar 58 Yellow-poplar - eastern hemlock 59 Yellow-poplar - white oak - northern red oak 60 Beech - sugar maple 62 Silver maple - American elm 76 Shortleaf pine - oak 78 Virginia pine - oak 108 Red maple 110 Black oak SRM (RANGELAND) COVER TYPES : NO-ENTRY HABITAT TYPES AND PLANT COMMUNITIES : American hazelnut is a dominant or codominant shrub in maple-basswood (Acer-Tilia) forests of Wisconsin and Minnesota . In Nebraska, American hazelnut is a dominant shrub in the ecotone of forest and prairie [1,33]. It is a dominant understory species in jack pine (Pinus banksiana), paper birch (Betula papyrifera), trembling aspen (Populus tremuloides), and northern pin oak (Quercus ellipsoidalis) communities of northern Wisconsin .
SPECIES: Corylus americana
IMPORTANCE TO LIVESTOCK AND WILDLIFE : The leaves, twigs, and catkins of American hazelnut are browsed by deer and moose [11,24]. The nuts are eaten by small mammals, northern bobwhite, ruffed grouse and other large birds, and deer [19.20]. Beaver eat the bark . PALATABILITY : NO-ENTRY NUTRITIONAL VALUE : American hazelnut has a fairly high protein and energy value. Percentage composition (dry weight) of the nuts is as follows : crude protein 25.81 crude fiber 2.10 available protein 23.25 calcium 0.28 phosphorus 0.39 COVER VALUE : NO-ENTRY VALUE FOR REHABILITATION OF DISTURBED SITES : NO-ENTRY OTHER USES AND VALUES : American hazelnut has been cultivated as an ornamental since 1798. It is also commercially cultivated for nut production. The sweet nuts may be eaten raw or ground and made into a cakelike bread . The nuts were used by Native Americans to flavor soups . OTHER MANAGEMENT CONSIDERATIONS : American hazelnut often competes with hardwoods and pines for light and moisture [25,27]. Because of shading and aggressive growth, it has long been recognized as a major deterrent to the successful regeneration of upland conifers . American and beaked hazelnut (C. cornuta) are responsible for much of the failure of red pine (Pinus resinosa) regeneration in Minnesota . American hazelnut can be controlled with herbicides [22,25].
SPECIES: Corylus americana
BOTANICAL AND ECOLOGICAL CHARACTERISTICS
GENERAL BOTANICAL CHARACTERISTICS : American hazelnut is a large, deciduous, rhizomatous shrub from 3 to 10 feet (1-3 m) tall [5,9]. It has a straight trunk with spreading, ascending branches, and can form dense thickets. The leaves are 3 to 5 inches (8-12 cm) long. The male catkins are 8 inches (20 cm) long, straight, slender, and regularly spaced along the upper stem. The female flowers are tiny, almost completely enclosed by bracts, and near the end of the twigs. The nuts are enclosed in two leafy bracts [20,28]. The roots are typically in the upper 6 inches (15 cm) of soil . Some of the smaller roots run vertically toward the surface and branch profusely into very fine laterals . RAUNKIAER LIFE FORM : Phanerophyte REGENERATION PROCESSES : American hazelnut reproduces both sexually and asexually. It begins producing seed after the first year, and produces good seed crops every 2 to 3 years. Seed dispersal is chiefly by mammals or birds . Vegetative Reproduction: The most important mode of reproduction of American hazelnut is from rhizomes . The large, woody rhizomes are 4 to 6 inches (10-15 cm) below the surface. Rhizomes give rise to new shoots 1 to 2 feet (30-60 cm) from the parent plant . SITE CHARACTERISTICS : American hazelnut occurs along streams, hedgerows, meadows, woodlands, roadsides, and forest margins. It grows best on rich, moist, well-drained soils [20,31,34] Common understory associates of American hazelnut include shagbark hickory (Carya ovata), raspberry (Rubus spp.), smooth sumac (Rhus glabra), chokecherry (Prunus virginiana), arrowwood (Viburnum rafinesquianum), eastern hophornbeam (Ostrya virginiana), and dogwood (Cornus spp.) [1,2,10]. SUCCESSIONAL STATUS : American hazelnut is shade tolerant . It can grow under a light intensity of 15 percent or less; even as low as 1 percent . It is a mid-seral species, and is usually absent in old-growth forest communities . SEASONAL DEVELOPMENT : The flowers of American hazelnut are formed in the summer and open the following spring, before the leaves emerge. By late summer or early fall, the fertilized flowers develop into fruits .
SPECIES: Corylus americana
FIRE ECOLOGY OR ADAPTATIONS : Low- to moderate-severity fires top-kill American hazelnut . It survives fire by sprouting from rhizomes [7,10]. The underground roots and rhizomes can survive low- to moderate-severity fires when the humus is moist. They are relatively shallow, however, and are vulnerable to fire when the humus is dry and combustible . POSTFIRE REGENERATION STRATEGY : Rhizomatous shrub, rhizome in soil Secondary colonizer - off-site seed 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".
SPECIES: Corylus americana
IMMEDIATE FIRE EFFECT ON PLANT : The aerial portions of American hazelnut are easily top-killed by spring and summer fires . PLANT RESPONSE TO FIRE : American hazelnut sprouts from rhizomes following fire . Annual burning can help control American hazelnut. On oak woodland sites in Minnesota, a series of annual fires reduced the American hazelnut frequency to 39 percent on burned plots compared to 65 percent on unburned plots. Although annual burning increased the density of hazelnut stems, stems on burned sites were shorter and smaller than stems on unburned sites, so total American hazelnut biomass was less on burned sites . See Fire Case Studies for more information on this study. A volume equation for determining biomass, growth response, and woody density for American hazelnut following fire has been developed . FIRE MANAGEMENT CONSIDERATIONS : In areas where fire has been excluded, a heavy density of American hazelnut has developed, suppressing desirable tree species and contributing to fuel buildup [10,21]. Repeated summer fires inhibit the ability of American hazelnut to sprout by exposing and damaging underground stems and roots and exhausting stored food reserves. Single fires may eliminate American hazelnut if humus is sufficiently dry to be completely consumed .
|Common name||Scientific name|
|American hazelnut||Corylus americana|
Axelrod, A. N.; Irving, F. D. 1978. Some effects of prescribed fire at Cedar
Creek Natural History Area. Journal of the Minnesota Academy of Science. 44(2):
Prescribed burning was conducted on the Cedar Creek Natural History Area in Anoka and Isanti counties, Minnesota.
The study sites are on Anoka sand plain upland soils, with fine sands in the Sartell and Zimmerman series. Topography is generally level .
PREFIRE PLANT COMMUNITY:
Cedar Creek Natural History Area contains bur oak-northern pin oak-quaking aspen (Quercus macrocarpa-Q. ellipsoidalis-Populus tremuloides) woodlands , marshlands, and old fields. The study sites were on the oak woodlands. American hazelnut clones dominated the understory, and there was an herbaceous ground layer. Based on the unburned control plots, prefire American hazelnut density was approximately 11 stems/milacre .
Study sites are classified in the following plant community and likely experienced the historic fire regime described below:
|Fire regime information on the vegetation community in which American hazelnut occurs in this study. Fire regime characteristics are taken from the LANDFIRE Rapid Assessment Vegetation Model . This vegetation model was developed by local experts using available literature, local data, and expert opinion as documented in the .pdf file linked from the Potential Natural Vegetation Group listed below.|
|Vegetation Community (Potential Natural Vegetation Group)||Fire severity*||Fire regime characteristics|
|Percent of fires||Mean interval
|Northern oak savanna||Replacement||4%||110||50||500|
|Surface or low||87%||5||1||20|
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.
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.
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 [36,37].
Fire prescription and behavior: Four fire treatment sites and an unburned control were selected for this study. Prescribed burning was conducted annually or on fire-and-rest cycles. A total of 19 prescribed fires were conducted on the 4 burn units. Seventeen of the fires were conducted in spring, with the earliest fire on 11 April 1969 and the latest on 16 May 1972. Surface fuels were oak litter and grasses (Poaceae). Fires on spring-burned sites were conducted before green-up, when surface fuels were mostly or completely cured. The majority of the prescribed fires were of moderate severity and fairly continuous; however, Site 3 experienced 2 low-severity, patchy summer fires before the moderate-severity April 1969 fire gave satisfactory fire continuity. April and May fires were ignited in the late afternoon, usually after 5:00 p.m., 3 to 10 days after measurable precipitation. Strip head fires were used.
|Stocking and treatment dates of prescribed-burn sites on Cedar Creek, MN|
|Site||Treatment||Area (acres)||1972 basal area (ft²)||Rx fire dates|
|Site 1||7 burns in 8 years||27||70||4 May 1965,
25 April 1966,
11 April 1967,
26 April 1968,
12 May 1969,
12 April 1971,
16 May 1972
|Site 2||8 burns in 8 years||25||42||4 May 1965,
13 April 1966,
5 May 1967,
26 April 1968,
12 May 1969,
4 May 1970,
3 May 1971,
25 April 1972
|Site 3||3 burns in 7 years||10||64||30 August 1966,
6 September 1967,
23 April 1969
|Site 4||1 burn in 5 years||27||61||14 May 1969|
|Site 5||unburned control||not provided||60||no recent fires|
Weather conditions on days of burning ranged as follows:
|Weather conditions and fire behavior for the Cedar Creek burns|
|Air temperature||Relative humidity||Windspeed||Rate of spread||Fuel consumption||Flame height*||Depth of flame front*|
|56-91 °F||26%-72%||1-20 mph||8-15 ft/min||917-6,500 lbs/acre||~2 in-3 ft||<1ft in grass fuels
~3 feet in thick oak litter
|*Flame height and flame front measures are for spring fires only. These measures were not provided for the summer fire on Site 3.|
Green-up had begun on some sites burned in late spring,, so herbaceous surface fuels were only partially cured. These late spring fires burned at lower severities, had slower rates of spread, and produced more smoke than the other spring fires.FIRE EFFECTS ON TARGET SPECIES:
|Overstory density and American hazelnut density, height, and biomass on study plots in the 4th postfire growing season. Data are means (SD).|
|Treatment||Oak overstory basal area (ft/acre)||American hazelnut basal area (stems/0.001 acre)||Stem height* (inches)||Stem biomass (g)|
|Site 1 (7 burns in 8 years)||70 (46)||19.2 (4.6)||16 (6.1)||16.3 (3.6)|
|Site 2 (8 burns in 8 years)||42 (68)||19.9 (8.4)||18 (6.1)||30.6 (16.4)|
|Site 3 (3 burns in 7 years)||64 (39)||8.0 (2.7)||34 (14)||117 (92.2)|
|Site 4 (1 burn in 5 years)||61 (51)||10.0 (6.2)||30 (9.4)||92.1 (49.4)|
|Site 5 (unburned control)||60 (44)||11.0 (4.6)||33 (14.2)||150.4 (85.3)|
|*For American hazelnut stem height, data are the means of the longest stem on each of 218 plots.|
Statistical analyses showed no significant differences (P=0.05 for all study measures) between either American hazelnut density or stem height on Sites 1 and 2, the annual burn treatments. Similarly, there were no significant differences in stem density or stem height between Sites 3 and 4, the treatments with rest years between fire treatments. Data for the 2 annual fire treatments were therefore pooled and compared to pooled data for the 2 fire-and-rest treatments. American hazelnut stocking was significantly denser on annually burned plots (Sites 1 and 2) compared to fire-and-rest plots (Sites 3 and 4), and American hazelnut stems were significantly taller on fire-and-rest plots (Sites 3 and 4) compared to annually burned plots. The authors attribute these differences to age variation in American hazelnut stems. Annually burned plots had only even-aged, 1-year-old stems. As time since fire increased on fire-and-rest plots, even-aged stems from the first postfire growing season were augmented with younger, shorter stems.
Both annual fire and fire-and-rest treatments initially reduced American
hazelnut stem density and height compared to the control; however, by fourth
growing season following 1 to 3 fires, there were no significant differences
between American hazelnut density, stem height, or biomass on fire-and-rest
plots compared to unburned plots. However, the series of annual fires
approximately doubled American hazelnut density and reduced mean stem height to
about one-half that of American hazelnut stems on unburned plots. Stems on
unburned plots were older and larger than stems on burned plots, so biomass of
unburned stems was approximately
4 times more than biomass of stems on annually burned plots.
FIRE MANAGEMENT IMPLICATIONS:
Fire management objective: The series of annual fires successfully controlled American hazelnut. Although density increased, the proportion of the understory occupied by American hazelnut was less due to reductions in height and biomass. Fire-and-rest treatments did not control American hazelnut.
Statistical analyses of the effects of the various fire treatments on the oak overstory were not provided. Based on overstory oak basal area, overstory stand structures were similar on fire-and-rest plots and control plots. The Site 1 annual burn plots had greater oak density than the fire-and-rest and control plots, while overstory density on the Site 2 annual burn plots was less than fire-and-rest and control plots. Further burning treatments on Cedar Creek and restoration fires on similar oak woodland/American hazelnut sites may help explain discrepancies in these study results.Fire control of American hazelnut: The authors recommend repeated burning on a regular schedule to restore and maintain oak savannas. Field observations by the authors suggested that grass and forb cover increased where American hazelnut height and biomass were reduced by annual burning. The effect of repeated fires on American hazelnut was temporary, however. In this study, American hazelnut regained most of its prefire biomass by the fourth postfire growing season on fire-and-rest sites. Axelrod and Irving  predict that if burning is conducted at less than 7-year intervals, American hazelnut will completely regain its prefire height and biomass. The results of this study suggest that a schedule of annual or nearly annual fires provides optimal American hazelnut control.
SPECIES: Corylus americana
REFERENCES : 1. Aikman, John M. 1926. Distribution and structure of the forests of eastern Nebraska. University Studies. 26(1-2): 1-75.  2. Alban, David H.; Perala, Donald A.; Schlaegel, Bryce E. 1978. Biomass and nutrient distribution in aspen, pine, and spruce stands on the same soil type in Minnesota. Canadian Journal of Forest Research. 8: 290-299.  3. Axelrod, A. N.; Irving, F. D. 1978. Effects of prescribed fire on American hazel at the Cedar Creek natural area in Minnesota. Restoration and Management Notes. 1(2): 14.  4. Bockheim, J. G.; Jepsen, E. A.; Heisey, D. M. 1991. Nutrient dynamics in decomposing leaf litter of 4 tree species on a sandy soil in northwestern Wisconsin. Canadian Journal of Forest Research. 21: 803-812.  5. Brinkman, Kenneth A. 1974. Corylus L. hazel, filbert. In: Schopmeyer, C. S., technical coordinator. Seeds of woody plants in the United States. Agric. Handb. 450. Washington, DC: U.S. Department of Agriculture, Forest Service: 343-345.  6. Buckman, Robert E. 1964. Effects of prescribed burning on hazel in Minnesota. Ecology. 45(3): 626-629.  7. Buckman, Robert E. 1965. Silvicultural use of prescribed burning in the Lake States. In: Proceedings--Society of American Foresters meeting; 1964 September 27 - October 1; Denver, CO. Washington, D.C.: Society of American Foresters: 38-40.  8. Buckman, Robert E. 1966. Estimation of cubic volume of shrubs (Corylus spp.). Ecology. 47(5): 858-860.  9. Chapman, William K.; Bessette, Alan E. 1990. Trees and shrubs of the Adirondacks. Utica, NY: North Country Books, Inc. 131 p.  10. Clark, James S. 1990. Twentieth-century climate change, fire suppression, and forest production and decomposition in northwestern Minnesota. Canadian Journal of Forestry Research. 20: 219-232.  11. Dalke, Paul D. 1941. The use and availability of the more common winter deer browse plants in the Missouri Ozarks. Transactions, 6th North American Wildlife Conference. 6: 155-160.  12. Eggler, Willis A. 1938. The maple-basswood forest type in Washburn County, Wisconsin. Ecology. 19(2): 243-263.  13. Eyre, F. H., ed. 1980. Forest cover types of the United States and Canada. Washington, DC: Society of American Foresters. 148 p.  14. Eyre, F. H.; Zehngraff, Paul. 1948. Red pine management in Minnesota. Circular No. 778. Washington, DC: U.S. Department of Agriculture. 70 p.  15. Garrison, George A.; Bjugstad, Ardell J.; Duncan, Don A.; [and others]. 1977. Vegetation and environmental features of forest and range ecosystems. Agric. Handb. 475. Washington, DC: U.S. Department of Agriculture, Forest Service. 68 p.  16. Gilmore, Melvin Randolph. 1919. Uses of plants by the Indians of the Missouri River region. 33rd Annual Report. Washington, DC: Bureau of American Ethnology. 154 p.  17. Gleason, Henry A.; Cronquist, Arthur. 1991. Manual of vascular plants of northeastern United States and adjacent Canada. 2nd ed. New York: New York Botanical Garden. 910 p.  18. Great Plains Flora Association. 1986. Flora of the Great Plains. Lawrence, KS: University Press of Kansas. 1392 p.  19. Gullion, G. W. 1970. Ruffed grouse investigations - influence of forest management practices on grouse populations. Upland Game Job No. 45. [St. Paul, MN]: Minnesota Department of Game and Fish. Game Research Quarterly Reports. 30(3): 104-105.  20. Hunter, Carl G. 1989. Trees, shrubs, and vines of Arkansas. Little Rock, AR: The Ozark Society Foundation. 207 p.  21. Paulsen, Harold A., Jr.; Miller, John C. 1968. Control of Parry rabbitbrush on mountain grasslands of western Colorado. Journal of Range Management. 21: 175-177.  22. Krefting, Laurits W. 1962. Use of silvicultural techniques for improving deer habitat in the Lake States. Journal of Forestry. 60(1): 40-42.  23. Kuchler, A. W. 1964. Manual to accompany the map of potential vegetation of the conterminous United States. Special Publication No. 36. New York: American Geographical Society. 77 p.  24. Pastor, J.; Dewey, B.; Naiman, R. J.; [and others]. 1993. Moose browsing and soil fertility in the boreal forests of Isle Royale National Park. Ecology. 74(2): 467-480.  25. Perala, Donald A. 1971. Controlling hazel, aspen suckers, and mountain maple with picloram. Res. Note NC-129. St. Paul, MN: U.S. Department of Agriculture, Forest Service, North Central Forest Experiment Station. 4 p.  26. Raunkiaer, C. 1934. The life forms of plants and statistical plant geography. Oxford: Clarendon Press. 632 p.  27. Shirley, Hardy L. 1932. Light intensity in relation to plant growth in a virgin Norway pine forest. Journal of Agricultural Research. 44: 227-244.  28. Stephens, H. A. 1973. Woody plants of the North Central Plains. Lawrence, KS: The University Press of Kansas. 530 p.  29. Stickney, Peter F. 1989. Seral origin of species originating in northern Rocky Mountain forests. Unpublished draft on file at: U.S. Department of Agriculture, Forest Service, Intermountain Research Station, Fire Sciences Laboratory, Missoula, MT; RWU 4403 files. 7 p.  30. U.S. Department of Agriculture, Soil Conservation Service. 1982. National list of scientific plant names. Vol. 1. List of plant names. SCS-TP-159. Washington, DC. 416 p.  31. Vines, Robert A. 1960. Trees, shrubs, and woody vines of the Southwest. Austin, TX: University of Texas Press. 1104 p.  32. Wainio, Walter W.; Forbes, E. B. 1941. The chemical composition of forest fruits and nuts from Pennsylvania. Journal of Agricultural Research. 62(10): 627-635.  33. Weaver, J. E. 1968. Prairie plants and their environment: A fifty-year study in the Midwest. Lincoln, NE: University of Nebraska Press. 276 p.  34. Weaver, J. E.; Kramer, Joseph. 1932. Root system of Quercus macrocarpa in relation to the invasion of prairie. Botanical Gazette. 94: 51-85.  35. Dijkstra, Feike A.; Wrage, Keith; Hobbie, Sarah E.; Reich, Peter B. 2006. Tree patches show greater N losses but maintain higher soil N availability than grassland patches in a frequently burned oak savanna. Ecosystems. 9(3): 441-452.  36. Hann, Wendel; Havlina, Doug; Shlisky, Ayn; [and others]. 2005. Interagency fire regime condition class guidebook. Version 1.2, [Online]. In: Interagency fire regime condition class website. U.S. Department of Agriculture, Forest Service; U.S. Department of the Interior; The Nature Conservancy; Systems for Environmental Management (Producer). Variously paginated [+ appendices]. Available: http://www.frcc.gov/docs/18.104.22.168/Complete_Guidebook_V1.2.pdf [2007, May 23].  37. LANDFIRE Rapid Assessment. 2005. Reference condition modeling manual (Version 2.1), [Online]. In: LANDFIRE. Cooperative Agreement 04-CA-11132543-189. Boulder, CO: The Nature Conservancy; U.S. Department of Agriculture, Forest Service; U.S. Department of the Interior (Producers). 72 p. Available: http://www.landfire.gov/downloadfile.php?file=RA_Modeling_Manual_v2_1.pdf [2007, May 24].  38. LANDFIRE Rapid Assessment. 2007. Rapid assessment reference condition models. In: LANDFIRE. U.S. Department of Agriculture, Forest Service, Rocky Mountain Research Station, Fire Sciences Lab; U.S. Geological Survey; The Nature Conservancy (Producers). Available: http://www.landfire.gov/models_EW.php