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Wildlife, Animals, and Plants |
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FIRE EFFECTS
IMMEDIATE FIRE EFFECT ON PLANT:Fire kills mature medusahead plants. Immature plants may be only top-killed by early-season fire, and regenerate by tillering [72,76]. Fire also destroys many viable medusahead seeds, but sufficient numbers remain uninjured that reduction in plant density is usually temporary [70,90].
DISCUSSION AND QUALIFICATION OF FIRE EFFECT:No entry
PLANT RESPONSE TO FIRE:Medusahead increases under frequent fires at the expense of native species and sometimes, cheatgrass. It promotes further frequent fire by increasing fuel loads [26,70]. Accumulated medusahead litter enables stand-replacement fires to occur in ecosystems such as low sagebrush sites that, under "pristine" conditions, may have been fire-resistant [10,107,110,111]. Wildfires in medusahead-infested areas usually minimally damage soil surfaces and soil erosion is limited, but enough medusahead seed survives to produce thinned, vigorous stand of multiculmed medusahead plants the following year. Within a few years, stand densities approach prefire levels [50]. In cheatgrass and medusahead wildfires, accumulation of litter and the rapidity at which the litter combusts lead to soil heating of such short duration that nitrate levels may increase. Wildfire-induced increases in soil nitrate in cheatgrass and medusahead-dominated areas are undesirable: Medusahead is nitrophilic and readily germinates in seedbeds with high nitrate levels. Near Alturas, California, a wind-driven wildfire rapidly spread across a medusahead-dominated area. The litter did not completely ash and there were still viable medusahead fruits in the lightly charred litter. Bioassays of the burned soil found over 6.2x106 germinable seeds of medusahead per acre (unpublished data; R. R. Blank, USDA/ARS, Reno, NV) [9]. Fire eliminates some medusahead seed and removes medusahead litter. It also places the remaining seed in contact with mineral soil where it can germinate and subsequently be destroyed by future treatments such as tillage and herbicide use [99]. Contact with aqueous slurries of heated soil significantly (p<0.05) reduced the rate and success of emergence of medusahead seedlings compared with a control [11].
DISCUSSION AND QUALIFICATION OF PLANT RESPONSE:Attempts have been made to destroy medusahead by prescribed burning in soft-dough stage to destroy the seed crop. Medusahead stands in the milk or early dough stage (late May or early June) are cured enough that they can carry a "light" fire that burns through the slender culms and arrests seed development [40]. However, a "substantial" number of seeds are not killed by fire [48]. Burning followed by seeding of perennial grasses may suppress medusahead [16]. If postfire revegetation efforts of medusahead-infested areas are not timely, erosion will expose the clay subsoil that the species frequently inhabits [10]. A controlled burn in early June on a ranch in the Redwood Valley, California, almost completely eliminated medusahead, and the area was still "relatively" free of medusahead 2 years later [40]. Another California study found that medusahead cover was significantly reduced (p=0.03) by 74% with prescribed burning in ungrazed prairie. Coverage was greatest with either summer grazing or no grazing and fire exclusion (p=0.013) [67].
FIRE MANAGEMENT CONSIDERATIONS:Wildfires facilitate replacement of native grasses with these annual grasses [36,73]. However, burning may be an effective means of reducing dominance if plants are burned early enough in the season to scorch culms and seeds, preventing seed maturation [29]. Compared to chemical or cultivation treatments, burning provides a relatively economical, although highly variable, means of controlling medusahead [76]. The heat of the fire should be concentrated to burn as many seeds in the head as possible. This can be achieved by having the fire move slowly so as to obtain complete fuel consumption. Slow, "hot" fires kill the greatest number of seeds, and this can be achieved by burning downhill or into the wind [69,71,76]. Because midday burns are frequently accompanied by variable winds that make control of the fire difficult, late afternoon burns are often recommended. Early-season burns, conducted before medusahead seeds have ripened, are effective if associated plants have dried enough to provide fuel for a fire [69]. Burning medusahead during the soft dough stage is effective because the high moisture content in the seed increases the effects of burning [71]. Dense patches of green medusahead will often remain unburned unless previously sprayed with oil. Some recommend later-season burns, after medusahead seeds have ripened but before they drop. Seeds of most herbaceous species will have dropped by then, and will be less susceptible to fire damage [69]. An effective management strategy in central Oregon is burning medusahead in late spring or early summer before the seeds have dropped off the plant, and following the next spring with an herbicide treatment of glyphosate after remaining seeds have germinated. However, this herbicide treatment is not recommended when reseeding is required since it is a broad-spectrum non-specific treatment [72]. It is recommended that reburning not occur more than once every 2 to 3 years if an adequate stand of forage plants is to be established [69]. A California study found medusahead burned well at relative humidity of 40 to 50% and temperature 60 to 70 degrees Fahrenheit (16-21 oC); however, a temperature of 90 degrees Fahrenheit (32 oC) and relative humidity of 30% was considered too severe [40]. In another test, best burning conditions for consuming medusahead were experienced around noon with air temperature of 99 degrees Fahrenheit (37 oC), relative humidity 23%, and wind speed of 11 mph (17 km/hr). Other California studies suggest that relative humidity of about 40% is not optimal for igniting dry grass [40,71]. Fire's effectiveness in reducing stands of medusahead on rangeland depends on burning conditions, including time of day and season of burn. Fire can be an effective tool in removing old medusahead litter, reducing density of medusahead stands, reducing the medusahead seed bank, and minimizing damage to desirable associated species. The following are conditions present during burns of medusahead-infested rangeland at the R. E. Shellhammer Ranch in Solano County, California 1959 [71].
Slow, hot fires are most desirable for reducing medusahead. In this study, the most effective control of medusahead was obtained by late afternoon fires that burned slowly (into a mild wind), ignited when seed was in the soft-dough stage [71]. Small roadside burns in southeastern Los Angeles ponderosa pine woodlands often become dominated by medusahead and cheatgrass. These communities often accumulate fuel contributing to repeated and increasingly larger fires. These cycles can be interrupted by immediate seeding in the burned areas with perennials. However, if the annuals are established, competition must be reduced before desirable perennial herbs, shrubs, and/or trees can establish. On sites marginal for conifers, a combination of all 3 is often desirable [21].
Related categories for SPECIES: Taeniatherum caput-medusae | Medusahead |
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