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Severe Fires (severe + fire)
Selected AbstractsBelow-ground ectomycorrhizal community structure in a recently burned bishop pine forestJOURNAL OF ECOLOGY, Issue 6 2000P. Grogan Summary 1,The effects of wildfire ash on ectomycorrhizal (EM) associations were investigated by sampling bishop pine (Pinus muricata, D. Don) seedlings from control and ash-removed plots 1.5 years after a severe fire in a northern Californian P. muricata forest. The below-ground community composition of EM at the site was characterized using molecular techniques (PCR-RFLP and nucleotide sequencing). 2,A total of 30 fungal taxa were observed, many of which differed in their distribution between treatment and control seedlings. However, most of the taxa that were distinctive to either treatment or control seedlings occurred only once across the site, precluding statistical detection of potential ash effects on EM community composition. There were no significant effects of ash removal on plot-level mycorrhizal community richness or diversity, and there were no distinct treatment-related clusters in a principal components analysis. 3,Analysis of the combined data indicated that numbers of fungal taxa per seedling, numbers of successive root depth increments colonized by the same taxon, and distances to neighbouring seedlings colonized by the same taxon, were randomly distributed across the site for the majority of mycorrhizal fungi. These distributional patterns suggest that the post-fire mycorrhizal community structure on P. muricata arose primarily from successful colonization by randomly distributed point-source fungal inocula within the upper mineral soil layer of the forest floor. 4,By comparison with pre-fire studies from similar P. muricata sites nearby, our data indicate that severe wildfire disturbance resulted in marked changes in mycorrhizal community composition, and a sharp increase in the relative biomass of ascomycetous fungi. [source] Developing a post-fire flood chronology and recurrence probability from alluvial stratigraphy in the Buffalo Creek watershed, Colorado, USA,HYDROLOGICAL PROCESSES, Issue 15 2001John G. Elliott Abstract Stratigraphic and geomorphic evidence indicate floods that occur soon after forest fires have been intermittent but common events in many mountainous areas during the past several thousand years. The magnitude and recurrence of these post-fire flood events reflects the joint probability between the recurrence of fires and the recurrence of subsequent rainfall events of varying magnitude and intensity. Following the May 1996 Buffalo Creek, Colorado, forest fire, precipitation amounts and intensities that generated very little surface runoff outside of the burned area resulted in severe hillslope erosion, floods, and streambed sediment entrainment in the rugged, severely burned, 48 km2 area. These floods added sediment to many existing alluvial fans, while simultaneously incising other fans and alluvial deposits. Incision of older fans revealed multiple sequences of fluvially transported sandy gravel that grade upward into charcoal-rich, loamy horizons. We interpret these sequences to represent periods of high sediment transport and aggradation during floods, followed by intervals of quiescence and relative stability in the watershed until a subsequent fire occurred. An alluvial sequence near the mouth of a tributary draining a 0·82 km2 area indicated several previous post-fire flood cycles in the watershed. Dendrochronologic and radiocarbon ages of material in this deposit span approximately 2900 years, and define three aggradational periods. The three general aggradational periods are separated by intervals of approximately nine to ten centuries and reflect a ,millennium-scale' geomorphic response to a closely timed sequence of events: severe and intense, watershed-scale, stand-replacing fires and subsequent rainstorms and flooding. Millennium-scale aggradational units at the study site may have resulted from a scenario in which the initial runoff from the burned watershed transported and deposited large volumes of sediment on downstream alluvial surfaces and tributary fans. Subsequent storm runoff may have produced localized incision and channelization, preventing additional vertical aggradation on the sampled alluvial deposit for several centuries. Two of the millennium-scale aggradational periods at the study site consist of multiple gravel and loam sequences with similar radiocarbon ages. These closely dated sequences may reflect a ,multidecade-scale' geomorphic response to more frequent, but aerially limited and less severe fires, followed by rainstorms of relatively common recurrence. Published in 2001 John Wiley & Sons, Ltd. [source] Ecological effects of changes in fire regimes in Pinus ponderosa ecosystems in the Colorado Front RangeJOURNAL OF VEGETATION SCIENCE, Issue 6 2006Rosemary L. Sherriff Abstract Question: What is the relative importance of low- and high-severity fires in shaping forest structure across the range of Pinus ponderosa in northern Colorado? Location: Colorado Front Range, USA. Methods: To assess severities of historic fires, 24 sites were sampled across an elevation range of 1800 to 2800 m for fire scars, tree establishment dates, tree mortality, and changes in tree-ring growth. Results: Below 1950 m, the high number of fire scars, scarcity of large post-fire cohorts, and lack of synchronous tree mortality or growth releases, indicate that historic fires were of low severity. In contrast, above 2200 m, fire severity was greater but frequency of widespread fires was substantially less. At 18 sites above 1950 m, 34 to 80% of the live trees date from establishment associated with the last moderate- to high-severity fire. In these 18 sites, only 2 to 52% of the living trees pre-date these fires suggesting that fire severities prior to any effects of fire suppression were sufficient to kill many trees. Conclusions: These findings for the P. ponderosa zone above ca. 2200 m (i.e. most of the zone) contradict the widespread perception that fire exclusion, at least at the stand scale of tens to hundreds of hectares, has resulted in unnaturally high stand densities or in an atypical abundance of shade-tolerant species. At relatively mesic sites (e.g. higher elevation, north-facing), the historic fire regime consisted of a variable-severity regime, but forest structure was shaped primarily by severe fires rather than by surface fires. [source] Three centuries of fire in montane pine-oak stands on a temperate forest landscapeAPPLIED VEGETATION SCIENCE, Issue 1 2010Serena R. Aldrich Abstract Question: What was the role of fire in montane pine-oak (Pinus-Quercus) stands under changing human land uses on a temperate forest landscape in eastern North America? Location: Mill Mountain in the central Appalachian Mountains, Virginia, US. Methods: A dendroecological reconstruction of fire history was generated for four stands dominated by xerophytic pine and oak species. The fire chronology began under presettlement conditions following aboriginal depopulation. Subsequent land uses included European settlement, iron mining, logging, and US Forest Service acquisition and fire protection. Results: Fires occurred approximately every 5 years until 1930 without any evidence of a temporal trend in fire frequency. Burning ceased after 1930. Area-wide fires affecting multiple pine stands were common, occurring at intervals of approximately 16 years. Most living pines became established during the late 1800s and early 1900s. Dead pines indicated that an older cohort established ca. 1730. Most hardwoods were established between the 1920s and 1940s. Conclusions: Except for fire protection, changes in land use had no discernible influence on fire frequency. Lightning ignitions and/or large fire extent may have been important for maintaining frequent burning in the 1700s, while fuel recovery may have constrained fire frequency during later periods. The disturbance regime appears to be characterized by frequent surface fires and occasional severe fires, insect outbreaks or other disturbances followed by pine recruitment episodes. Industrial disturbances appear to have had little influence on the pine stands. The greatest impact of industrial society is fire exclusion, which permitted hardwood establishment. [source] | ||||||||||