• FIRE ECOLOGY OR ADAPTATIONS
• POSTFIRE REGENERATION STRATEGY

FIRE ECOLOGY OR ADAPTATIONS:

Fire regimes: The expansion of exotic annual grasses such as medusahead has substantially increased frequency of fire in the western United States [65]. Medusahead has a fine structure and its herbage dries completely; therefore, its standing dead biomass is extremely flammable. The hazard of wildfire is further increased by considerable litter [39]. Medusahead litter decomposes more slowly than that of most plants [99], therefore making stands of this annual grass a fire hazard [77]. Slow decomposition is a result of its high silica content [71,95]: total ash content of medusahead contains 72 to 89% silica [95]. The long-lasting litter formed by medusahead is easily ignited and burns readily [72]. Invasion can initiate a cycle where a non-native grass colonizes an area and provides the fine fuel necessary for the initiation and propagation of fire. Fires then increase in frequency, area, and possibly severity. Following these grass-fueled fires, non-native grasses recover more rapidly than native species and cause a further increase in fire [26]. Frequent fires destroy the shrub component of the plant community, and potentially part of the bunchgrass community, without destroying "significant" amounts of medusahead seed [72].

The non-native grasses cheatgrass and medusahead have invaded the low sagebrush communities on the volcanic tablelands of northeastern California and northwestern Nevada. When precipitation is adequate, the interspaces between sagebrush plants are completely covered by these invasive grasses. The fine fuels of these plants, and the accumulation of litter of highly siliceous medusahead, create conditions in which fire is easily carried. Negative effects of wildfires in this region include erosion of the thin, coarse-textured, eolian veneer soils [10]. For example, the herbaceous vegetation of a ponderosa pine/Sandberg bluegrass in Modoc County, California, included many other native herbaceous species. After a wildfire, medusahead excluded almost all other understory species [21].

Historically, the Snake River Plains of Idaho was vegetated with shrub-bunchgrass communities. The primary disturbance was patchy stand-replacement fire, occurring every few decades. Fire usually occurred where sagebrush or other shrubs had grown dense, since bunchgrasses did not often provide adequate continuous fuels. With invasion of exotic annuals and increase such as medusahead, historical patterns of postfire succession were altered. Fire-free intervals have been reduced, and shrub-bunchgrass lands are being converted to annual grassland. According to Peters and Bunting [81], "the landscape has become more homogenous, species diversity has decreased, and burns are larger and more continuous."

The range of fire intervals reported for some species that dominate communities in which medusahead occurs are listed below. To learn more about the fire regimes in those communities refer to the FEIS summary for the dominant species, under "Fire Ecology or Adaptations."

POSTFIRE REGENERATION STRATEGY [94]:

Related categories for SPECIES: Taeniatherum caput-medusae | Medusahead