The interaction of fire, fuels, and climate across Rocky Mountain forests

Understanding the relative influence of fuels and climate on wildfires across the Rocky Mountains is necessary to predict how fires may respond to a changing climate and to define effective fuel management approaches to controlling wildfire in this increasingly populated region. The idea that decades of fire suppression have promoted unnatural fuel accumulation and subsequent unprecedentedly large, severe wildfires across western forests has been developed primarily from studies of dry ponderosa pine forests. However, this model is being applied uncritically across Rocky Mountain forests (e.g., in the Healthy Forests Restoration Act).We synthesize current research and summarize lessons learned from recent large wildfires (the Yellowstone, Rodeo-Chediski, and Hayman fires), which represent case studies of the potential effectiveness of fuel reduction across a range of major forest types. A “one size fits all” approach to reducing wildfire hazards in the Rocky Mountain region is unlikely to be effective and may produce collateral damage in some places.Keywords: Fire ecology, Climate, Rocky Mountain forests, Forest health, Forest managementKeywords: Fire ecology, Climate, Rocky Mountain forests, Forest health, Forest managemen

The interaction of fire, fuels, and climate across Rocky Mountain forests

Understanding the relative influence of fuels and climate on wildfires across the Rocky Mountains is necessary to predict how fires may respond to a changing climate and to define effective fuel management approaches to controlling wildfire in this increasingly populated region. The idea that decades of fire suppression have promoted unnatural fuel accumulation and subsequent unprecedentedly large, severe wildfires across western forests has been developed primarily from studies of dry ponderosa pine forests. However, this model is being applied uncritically across Rocky Mountain forests (e.g., in the Healthy Forests Restoration Act). We synthesize current research and summarize lessons learned from recent large wildfires (the Yellowstone, Rodeo-Chediski, and Hayman fires), which represent case studies of the potential effectiveness of fuel reduction across a range of major forest types. A “one size fits all” approach to reducing wildfire hazards in the Rocky Mountain region is unlikely to be effective and may produce collateral damage in some places.Keywords: climate, forest health, Rocky Mountain forests, forest management, fire ecolog

Fire and Landscape Diversity in Subalpine Forests of Yellowstone National Park

Fire history was determined by fire scar analysis in a subalpine watershed in Yellowstone National Park, Wyoming, USA. Evidence was found for 15 fires since 1600, of which 7 were manor fires that burned \u3e 4 ha, destroyed the existing forest, and initiated secondary succession. Most of the upland forest area was burned by large, destructive fires in the middle and late 1700\u27s. Fires since then have been small and have occurred at long intervals. Fire frequency in this area is partly controlled by changes in the fuel complex during succession. Fuels capable of supporting a crown fire usually do not develop until a stand is 300-400 yr old, and ignitions prior to that time usually extinguish naturally before covering more than a few hectares. Thereafter a destructive crown fires is likely whenever lightning ignites small fuels during warm, dry, windy weather. On the extensive subalpine plateaus of Yellowstone National Park there appears to be a natural fire cycle of 300-400 yr in which large areas burn during a short period., followed by a long, relatively fire-free period during which a highly flammable fuel complex again develops. The study area appears to be about midway between major fire events in this cycle. This, rather than human fire suppression, apparently is the major reason for the small number and size of fires in the area during the last 180 yr. On the basis of the fire history data, the sequence of vegetation mosaics during the last 200 yr was reconstructed for the watershed. Indices of landscape diversity were computed for each reconstruction, treating forest types and successional stages as taxa and incorporating components of richness, evenness, and patchiness. Landscape diversity was highest in the early 1800\u27s following the large fires in the 1700\u27s, then declined in the late 1800\u27s during a 70—yr period when no major fires occurred and the landscape was dominated by even—aged forests developing on the areas burned in the 1700\u27s. Landscape diversity has increased somewhat during the last half—century as a result of two small fires and the effects of the mountain pine beetle. These landscape reconstructions for the last 200 yr suggest that the Yellowstone subalpine ecosystem is a nonsteady—state system characterized by long—term, cyclic changes in landscape composition and diversity. Such cyclic patterns may significantly influence wildlife habitat, streamflow, nutrient cycling, and other ecological processes and characteristics within the Park, and they may be an important consideration in judging whether recent ecological changes are natural or man induced. The landscape reconstructions were also made using a simulation model based on hypothetical fire management policies of total fire exclusion and selective fire control (permitting only small fires to burn). These hypothetical management policies generally reduced the richness and patchiness of the landscape compared to the natural fire regime, but they increased the evenness and reduced the magnitude of periodic fluctuations in overall landscape diversity. At times, overall landscape diversity may actually be higher with a fire control policy than with a natural fire regime. At other times, fire significantly increases landscape diversity, as would be expected

Natural disturbance by tree falls in old-growth mixed mesophytic forest: Lilley Cornett Woods, Kentucky

Natural disturbance by tree-falls has been monitored since 1973 on a 104-ha tract of old-growth mixed mesophytic forest at Lilley Cornett Woods in southeastern Kentucky. During this time, 77 gaps have been recorded. Mean gap size is 374 m2, median size is 2307 m2, and the range of gaps observed to date is from 74 m to 1235 m2. Gap formation varies greatly by season and year. The largest number of treefalls usually occurs in the summer from June through August. Tree-fall appears unrelated to regional weather patterns, but may be strongly influenced by local windstorms of high velocity and brief duration° Sudden death of American beech (Fagus .grandifolia) by overthrow or stem breakage is the most frequent cause of gaps, Although beech is also the most frequent tree with large boles in the forest, a greater proportion of gaps are formed than would be predicted from its density, probably because of its high incidence of hollow stems, and shallow root systems. More gaps are formed by large trees breaking off above # the ground than by overturning. Slope positions and form do not appear to strongly influence tree-fall frequency. Seven estimates of canopy turnover time are given, based on two different methods, The disturbance regime of scattered gaps formed in an uneven-aged forest suggests that the Woods provides an example of the shifting mosaic steady-state model of forest development. Whether or not the Woods is an area that provides all developmental stages of this model depends on definition of forest composition, continued long-term monitoring, and refinement of estimates of canopy turnover time. Our best estimate of canopy turnover time is 269 years, but this figure still represents a general estimate because different methods of calculation give different results

Aspen\u27s Ecological Role in the West

Aspen exhibits a variety of ecological roles. In southern Colorado, the 1880 landscape mosaic contained a range of stand ages, of which half were \u3e70 years old and half were younger. Pure aspen stands in southern Colorado are widespread and may result from previous short fire intervals that eliminated local conifer seed sources. Aspen regeneration in northern Yellowstone Park is controlled by ungulate browsing pressure and fire, so it has been limited since 1920. However, an episode of aspen seedling establishment occurred after the 1988 fires. We urgently need additional detailed, local case studies of aspen ecology to inform management decisions

Age structure of aspen forests on the Uncompahgre Plateau, Colorado

Aspen forests are one of the most dynamic forest types in western North America, responding to chronic factors of competition for resources, as well as episodes of intense herbivory, drought, and fires. The interactions of these driving factors lead to varying age structures of aspen across landscapes and through time. We characterized the age structure of aspen trees on the Uncompahgre Plateau in western Colorado, USA, to inform collaborative efforts of landscape-scale forest restoration. Over 1000 cores from 51 locations showed few aspen older than 140 years (\u3c0.5% for aspen numbers, \u3c2.5% of aspen basal area). Heavy recruitment in the late 1800s (following the last major fires) led to cohorts from 100 to 140 years of age that account for 15% of current aspen numbers and 40% of current aspen basal area. Perhaps the most important character of the current age structure is a relatively low number of aspen younger than 50 years; normal rates of tree survivorship in coming decades will lead to a substantial decline in aspen on the Plateau as these cohorts progress into older age classes. Patterns of aspen ages on the Uncompahgre Plateau differ substantially from those on the Kaibab Plateau and in Rocky Mountain National Park, owing the varying importance in space and time of driving factors. Landscape-scale increases in aspen regeneration (from major events such as fire) would be necessary to moderate the long-term decline in aspen on the Uncompahgre Plateau

Interaction of Fire, Fuels, and Climate Across Rocky Mountain Forests

Understanding the relative influence of fuels and climate on wildfires across the Rocky Mountains is necessary to predict how fires may respond to a changing climate and to define effective fuel management approaches to controlling wildfire in this increasingly populated region. The idea that decades of fire suppression have promoted unnatural fuel accumulation and subsequent unprecedentedly large, severe wildfires across western forests has been developed primarily from studies of dry ponderosa pine forests. However, this model is being applied uncritically across Rocky Mountain forests (e.g., in the Healthy Forests Restoration Act). We synthesize current research and summarize lessons learned from recent large wildfires (the Yellowstone Rodeo-Chedisk, and Hayman fires), which represent case studies of the potential effectiveness of fuel reduction across a range of major forest types. A one size fits all approach to reducing wildfire hazards in the Rocky Mountain region is unlikely to be effective and may produce collateral damage in some places