Stand-replacing Fire Research Articles

Spatial Controls of Pre?Euro-American Wind and Fire Disturbance in Northern Wisconsin (USA) Forest Landscapes

We elucidate spatial controls of wind and fire disturbance across northern Wisconsin (USA), where climatic and topographic gradients are not strong, using data from the original US Public Land Survey (PLS) notes. These records contain information on the location and extent of heavy windthrows and stand-replacing fires prior to Euro-American settlement. The spatial patterns of windthrow and fire were spatially clustered at all scales in this historical environment, with stronger associations at local than regional scales. Logistic regression shows environmental variables to have a strong influence on this pattern. In the case of heavy windthrow, environmental drivers of disturbance pattern are fairly consistent across the region. The effects of climate and vegetation are predominant at all scales, but effects are often indirect, with strong interactions between them. Interactions between these two drivers and soil characteristics are also sometimes present. In contrast, models of stand-replacing fire show simple and direct control within and across fire-prone landscapes of historical northern Wisconsin, with climate and physiography as the main factors explaining the distribution of fire disturbance. This simple and direct control is lost at the regional scale, where climate, physiographic, soil, and vegetation variables, along with interactions between them, are significant factors. Contrary to other regions, the topographic effects are generally not important in predicting either wind or fire disturbance. Our work suggests that, in landscapes that lack strong environmental patterning, climate maintains its role as a primary driver of these natural disturbances, but topography is replaced by interactions and feedbacks with other forms of environmental heterogeneity.

Understanding a flammable planet – climate, fire and global vegetation patterns

Understanding a flammable planet – climate, fire and global vegetation patterns

Associations between Forest Fire and Mexican Spotted Owls

Abstract In 1993, the US Fish and Wildlife Service listed the Mexican spotted owl (Strix occidentalis lucida) as threatened, in part because of the rising threat to its habitat from stand-replacing wildfires. In 1997, we surveyed 33 owl sites that, in the previous four years, had burned at various levels ranging from light controlled burns to stand-replacing fires. We compared owl occupancy and reproduction in these burned sites to 31 unburned owl sites with similar habitat and topography. Although unburned sites showed higher proportions of both occupancy and reproduction, the negative relationship observed between recent fire occurrence and owl occupancy rank was statistically weak (Test for Marginal Homogeneity, P = 0.110). Owls tended not to be present where pure pine stands (Pinus spp.) comprised a large proportion (38–85%) of burned sites, but no other factors relating to habitat or fire severity had a significant, biologically interpretable influence on occupancy rank. We suspect that relatively low-intensity ground fires, including most prescribed fires, probably have little or no short-term impact on Mexican spotted owl presence or reproduction, but we have no data on long-term effects of fire. We recommend proactive fuels-management treatments in areas not currently occupied by owls as a means of reducing fire risk in areas occupied by owls. Within areas occupied by owls, judicious treatments may be appropriate after case-by-case evaluations of potential benefits and risks within those sites. FOR. SCI. 50(6):765–772.

Fire-induced erosion and millennial-scale climate change in northern ponderosa pine forests

Western US ponderosa pine forests have recently suffered extensive stand-replacing fires followed by hillslope erosion and sedimentation. These fires are usually attributed to increased stand density as a result of fire suppression, grazing and other land use, and are often considered uncharacteristic or unprecedented. Tree-ring records from the past 500 years indicate that before Euro-American settlement, frequent, low-severity fires maintained open stands. However, the pre-settlement period between about ad 1500 and ad 1900 was also generally colder than present, raising the possibility that rapid twentieth-century warming promoted recent catastrophic fires. Here we date fire-related sediment deposits in alluvial fans in central Idaho to reconstruct Holocene fire history in xeric ponderosa pine forests and examine links to climate. We find that colder periods experienced frequent low-severity fires, probably fuelled by increased understory growth. Warmer periods experienced severe droughts, stand-replacing fires and large debris-flow events that comprise a large component of long-term erosion and coincide with similar events in sub-alpine forests of Yellowstone National Park. Our results suggest that given the powerful influence of climate, restoration of processes typical of pre-settlement times may be difficult in a warmer future that promotes severe fires.

Spatial heterogeneity of lodgepole pine sapling densities following the 1988 fires in Yellowstone National Park, Wyoming, USA

Large disturbances create spatial heterogeneity in vegetation re-establishment, and documenting such variability is critical for understanding and predicting succession. We quantified the spatial heterogeneity of lodgepole pine sapling densities 10 years after the 1988 fires in Yellowstone National Park using color infrared orthophotographs. Densities were classified across the landscape at an accuracy of 70.9%, and landscape metrics were used to characterize their spatial variability. Densities ranged from 0 to > 500 000 saplings/ha, but >60% of the burned area was represented by densities <5000 stems/ha. The burned area consisted of small patches averaging 1.5 ha in area at a mean patch density of 68 patches/100 ha. Densities occurred in nearly equal proportions across the landscape (Shannon's evenness = 0.85) but were well dispersed (contagion index ≈ 20%), suggesting that densities varied in a complex, fine-grained mosaic across the landscape, with high-density patches occurring within a matrix of larger, lower density patches. High-density patches were similar in area to severe surface fires, suggesting that burn severity is an important explanatory variable for spatial variation in sapling density. Large, stand-replacing fires may result in heterogeneous forest landscapes rather than homogenous forests of uniform structure, which may have important consequences for postfire ecological processes.

Assessing Fire Risk in the Wildland-Urban Interface

Abstract Identifying areas of the wildland-urban interface (WUI) that are prone to severe wildfire is an important step in prioritizing fire prevention and preparedness projects. Our objective is to determine at a regional scale the relative risk of severe wildfire in WUI areas and the numbers of people and houses in high-risk areas. For a study area in northern lower Michigan, we first develop a spatial database of WUI areas (both intermix and interface) using housing data from the 2000 US Census and 1994 vegetation data from the Gap Analysis Project of the Michigan Department of Natural Resources. Then, we develop a spatial database of historic (pre-1900) fire regimes and current (1994) fuels to identify areas with high risk of stand-replacing fires. High-risk areas historically supported jack pine (P. banksiana Lamb.) and mixed pine forests with stand-replacing fire rotations less than 100 years and currently support upland conifer and hardwood forests. Analysis of the databases shows that 26% of the study area is WUI. About 25% of the WUI has relatively high fire risk. Over 88% of the WUI with high fire risk has low housing density (<1 house per 2 ha) and is classified as intermix where fuels and structures intermingle. The predominance of high-risk intermix areas with low-density housing has implications for planning effective fuel treatments and evacuation plans.

A KEYSTONE SELECTIVE AGENT? PINE SQUIRRELS AND THE FREQUENCY OF SEROTINY IN LODGEPOLE PINE

Serotiny is a key life history trait in fire-prone habitats that is favored in plants that experience stand-replacing fires within their average life span. Although variation in fire frequency has been the focus of most studies attempting to understand variation in serotiny among populations and species of plants, other factors can select against serotiny. One agent in particular that can select against serotiny is an efficient pre-dispersal seed predator that eats a large fraction of the seeds held in the canopy. To test whether selection by such a predator selects against serotiny, we compared levels of serotiny in fire-adapted Rocky Mountain lodgepole pine (Pinus contorta ssp. latifolia) in five ranges lacking its dominant pre-dispersal seed predator, the pine squirrel (Tamiasciurus hudsonicus) to 344 stands with pine squirrels. Where pine squirrels were absent, the frequency of serotiny was consistently near 100%, whereas where squirrels were present, the frequency was variable, rarely approached the high levels found in areas without squirrels, and averaged much less than 50%. This indicates that squirrels select against serotiny and that, in the absence of squirrels, the frequency of serotiny would probably be uniformly higher throughout much of the Rocky Mountains. Because serotiny levels also influence the density of seedlings following a fire, squirrels, by selecting strongly against serotiny, have the potential to alter the early stages and perhaps the course of succession and various community attributes.

Historical and recent fire regimes in Piñon–Juniper woodlands on Mesa Verde, Colorado, USA

The fire history of Piñon–Juniper ( Pinus edulis– Juniperus osteosperma) woodlands in much of the southwestern United States is poorly understood, and as a result, fire management decisions are being made without a rigorous ecological underpinning. We investigated the historic fire regimes in Piñon–Juniper woodlands on the Mesa Verde cuesta utilizing stand and age structures. All Piñon trees in eight stands were aged and stand age was extrapolated to the surrounding landscapes using digital imagery, creating a time-since-fire map of the 1995 landscape. Six sampled stands were over 400 years, while two were between 200 and 300 years. Stand-replacing fire with a rotation of 400 years or longer characterized this Piñon–Juniper landscape before 1995; low-severity surface fires apparently have never been an important component of the fire regime in Mesa Verde. Superposed epoch analysis revealed that large fires occur following significantly low precipitation in May or in the winter (October–March) preceding a summer fire season. Since the mid-1990’s, a severe drought has characterized climate in this region, but the recent drought is similar to previous drought periods since 1950. A combination of canopy fuel build-up during two wet decades before 1995 and the current drought conditions has resulted in unprecedented fire activity (six large wildfires between 1996 and 2003) when compared with the reference period 1700–1900. We may be witnessing a unique period in the ecological history of the southwest, a period when vegetation patterns are being altered over extensive areas within a very short time. If the current drought continues, we ultimately may lose much of the old-growth Piñon–Juniper woodland in the southwest. We emphasize however, that these changes are not due to fire suppression or other direct human intervention but rather result from natural ecological responses to climatic variability. Therefore, our data provide no ecological justification for aggressive management activities such as mechanical fuel reduction or prescribed burning, except in the immediate vicinity of vulnerable cultural resources.

Hydrologic controls on the survival of Water Howellia ( Howellia aquatilis) and implications of land management

Water Howellia ( Howellia aquatilis) is a rare and endangered wetland plant listed as a threatened species under the Federal Endangered Species Act. 70% of the world population is found in the 1.7×10 5 ha Swan Valley, Montana, USA in wetlands of usually less than 1-ha. Survival of this aquatic species requires emergence during mid-summer, the drying out of occupied portions of the wetlands, a slight refilling of the wetlands in fall, and wetland re-establishment in the spring. This project was designed to establish the water source and seasonal controls on stage variation. Research approaches included water budgets derived from extensive micro-basin field measurements, including evaluation of ground water-surface water interaction, and standard geochemical analyses. Potential impacts to the wetland water balance from timber harvesting or stand replacement fires were evaluated using the WRNSHYD ® model. Results from two field seasons indicate that ground water inflow and plant transpiration control wetland stage. Snow survey recharge estimates, horizontal and vertical hydraulic gradient observations, seepage meter flux rates, wetland and ground water quality and the ground water inflow component of the water balance support the hypothesis that seasonal changes in the wetland are driven by a localized ground water flow system. Modeling predicts an increase in micro-basin water yield due to decreased plant transpirational water loss when watershed trees are removed by harvesting or a stand replacing fire. The duration of a potential increase in water yield is unknown.

Life histories of Mediterranean pines

The life history of Spanish pines and their relation to fire as the main disturbance factor in their ecosystems was analysed. The primary ecological attributes studied were the canopy seed bank (onset of cone production, percentage and persistence of serotinous cones), seed and cone morphology, sprouting and bark thickness. Four ecological groups were separated using multivariate cluster analysis and their life-history characteristics are discussed. Serotiny and early flowering in Pinus halepensis and P. pinaster reflect their evader strategy in relation to fire as this character is advantageous to survive frequent crown fires and to attain successful post-fire recruitment. Late flowering and absence of serotinous cones in P. nigra, P. sylvestris and P. uncinata indicate that their natural forest did not evolve under frequent crown fires. P. canariensis and P. pinea appeared in two single groups because of their sprouting capability and their seed size respectively. Intraspecific variation in P. pinaster was also analysed using the same criteria and high variability was found in its life history traits. A group of P. pinaster populations showed high levels of serotiny and thin bark as a possible adaptation to frequent stand-replacing crown fires. In contrast, a group of non- or weakly-serotinous populations seems to have evolved under a low-intensity fire regime where the best fitness corresponds to thick-barked individuals capable of surviving ground fires. Intermediate strategies were also evident in this species and were discussed in relation to the effect of different fire regimes caused by the understorey vegetation.

Landscape Heterogeneity and Disturbance Interactions in a Subalpine Watershed in Northern Colorado, USA

Three major disturbances affect subalpine forests in the Rocky Mountains: blowdown, insect outbreaks, and fire. These disturbances may influence one another temporally and spatially, creating a mosaic of disturbance patches. In 1997, a severe windstorm blew down trees on over 10,000 ha of subalpine forest in northern Colorado. Did previous disturbances influence the spatial pattern of blowdown in a representative part of the blowdown in the Middle Fork Elk River watershed? Dendrochronological evidence and a geographic information system were used to reconstruct the disturbance history, and the relationship between disturbance history (i.e., patch age) and the 1997 blowdown was examined. The fire regime varies temporally and spatially, with an area-weighted mean fire interval/fire rotation of 108 to 195 years. Stand-replacing fires appear to have had the most impact on the fire regime, but evidence of non-stand-replacing fires was also found. South-facing, lower-elevation slopes were the settings most likely to burn. Low-severity spruce-beetle disturbance was found in the mid-1700s and mid- to late 1800s, possibly related to regional outbreaks. Sheep-grazing and fire suppression may have influenced tree-regeneration and fire-frequency patterns. Each disturbance event occurred with varying severity across the landscape, influenced, in part, by the patterns of severity of previous disturbances. Patch age contributed to the pattern of the 1997 blowdown, but the relationship is complicated. The vegetation mosaic influenced spatial patterns of blowdown, resulting in new complexity and maintaining landscape heterogeneity.

Splitting in Fire-Killed Trees in the Boreal Forest of Alberta

Abstract Tree boles in the boreal forests of Alberta, Canada will split once killed by a stand-replacing crown fire. A total of 1,485 fire-killed trees were sampled, 1 yr after burning, in 23 plots in 14 widely separated stands within a 370,000 ha fire. Sampling occurred in the Upper and Lower Foothills natural subregions. The frequency of splitting varied by species but averaged 41% for all species. The order in the frequency of splitting was balsam fir, black spruce, white spruce and lodgepole pine. The type of splitting (straight, spiral, or multiple) varied by species, as did the position of the split on the tree bole. Aspect or solar angle was not statistically related to the type or occurrence of splitting.

THE INFLUENCE OF FIRE INTERVAL AND SEROTINY ON POSTFIRE LODGEPOLE PINE DENSITY IN YELLOWSTONE NATIONAL PARK

The time interval between stand-replacing fires can influence patterns of initial postfire succession if the abundance of postfire propagules varies with prefire stand age. We examined the effect of fire interval on initial postfire lodgepole pine (Pinus contorta var. latifolia Engelm.) density in Yellowstone National Park (YNP) following the 1988 fires. We asked whether postfire propagule abundance, measured as prefire percent serotiny, varied with fire interval and could explain patterns in postfire succession. The response of lodgepole pine density to variation in fire interval was explained by spatial and temporal variation in prefire serotiny. At low elevations, postfire lodgepole pine recruitment correlated strongly with prefire percent serotiny, which varied nonlinearly with prefire stand age. As a result, postfire lodgepole pine densities varied nonlinearly with fire interval. In contrast, at high elevations serotiny was low, varied little with stand age and did not influence postfire lodgepole pine densities, although, fire interval was still a significant predictor of postfire densities. At high elevations, fire interval varied nonlinearly with postfire lodgepole densities, presumably due to the temporal variation in propagule abundance from open cones in adjacent unburned stands. Temporal variation in stand-level serotiny at low elevations was best explained by age of individual trees. Logistic regression indicated that trees expected to be serotinous had a low probability of exhibiting serotiny at a young age, with increasing probability as trees matured up to 140 yr. This increase in serotiny with tree age likely accounts for the initial increase in stand-level percent serotiny with stand age at low elevations. The spatial variation in serotiny was correlated with variation in historical fire regimes. Fire interval models derived from lower elevations in YNP indicate that fire occurred historically at 135–185-yr intervals, whereas at higher elevations fires occurred at 280–310-yr intervals. The spatial patterns of serotiny appear to have been influenced by variability in historical fire regimes across the Yellowstone landscape, which has conditioned contemporary successional responses to disturbance.

Comment on "Aging discrepancies of white spruce affect the interpretation of static age structure in boreal mixedwoods"

There have been a recent series of papers that have documented underestimation of the age of boreal forest conifers. DesRochers and Gagnon (1997) demonstrated that excavation, serial sectioning to locate the root collar, and detailed dendrochronological analysis of aboveand below-ground sections (cross-dating) of the lower stem of black spruce (Picea mariana (Mill.) BSP) is necessary for exact age estimates. This has been further demonstrated on balsam fir (Abies balsamea (L.) Mill.) by Parent et al. (2000, 2002) and Parent and Morin (2002), and for a variety of boreal mixedwood species by Gutsell and Johnson (2002). Peters et al. (2002) have demonstrated the same difficulties in aging white spruce (Picea glauca (Moench) Voss). We have two objectives in writing this comment on the Peters et al. (2002) paper: (1) To clarify and discuss the issue of the timing of white spruce recruitment in boreal forests. We are concerned that Peters et al. (2002) will lead readers to believe that recruitment of white spruce in boreal mixedwood forests occurs only for a short period immediately after disturbance. (2) We also wish to discuss the place of very accurate but expensive techniques versus less accurate and inexpensive techniques in stand dynamics research. Peters et al. (2002) report the age structure and aging error for white spruce from nine 7-year-old and three older boreal mixedwood stands. They found a 2.4-year mean underestimate of time of establishment in a 20-year-old stand and a 6.4-year underestimate in two 38-year-old stands if tree sections were cut at ground level and rings counted, compared with ages determined by excavation to the root collar and careful cross-dating. Their conclusions were that “previous assumptions that age of white spruce can be accurately determined by ring counts at ground level (Youngblood 1995; Lieffers et al. 1996; Galipeau et al. 1997) are not valid in mixedwood stands in Alberta”, and “the mean number of missing rings found for trees in 38-year-old stands (6.4) nearly accounts for the regeneration lags and extended regeneration duration typically observed in non-cross-dated older stands (Youngblood 1995; Lieffers et al. 1996)”, and “aging errors have led to inaccurate depiction of regeneration patterns during early mixedwood stand development”. We are concerned that readers of Peters et al. (2002) will conclude that recruitment of spruce occurs almost exclusively in a short period after disturbance and that previous studies indicating that recruitment is sometimes delayed or extended were in error. From our reading of these three older papers cited in Peters et al. (2002), we believe that the authors would still have come to the same conclusions that they state in their papers even if they had aged their stands by excavation and cross-dating (assuming similar errors in aging). These papers’ general conclusions were that white spruce recruitment often begins immediately or shortly after disturbance, but in some stands or conditions the recruitment is delayed or extended over a long time period. The data from 46to 86-year-old Alberta stands in Lieffers et al. (1996) show two of nine stands with at least a 20-year delay before spruce recruitment began, and all sites with continuing spruce recruitment for 15–65 years. Youngblood (1995) found white spruce recruitment periods extending for more than 100 years based on ground-level age, although he did not sample all the spruce in his stands. Galipeau et al. (1997) found an initial 20-year white spruce recruitment pulse was followed by a second pulse beginning 40 years after fire in their 70-year-old stand. Even if the ground-level aging error increases with stand age, as Peters et al. (2002) suggest, the magnitude of the errors they found is certainly not large enough to eliminate these recruitment lags and prolonged recruitment periods. Peters et al. (2002) reported data on only three older stands with a narrow range of conditions; in all of their stands the stand-replacing fire was synchronous with a mast year, and there were ample mature spruce seed trees at time of disturbance. In boreal mixedwoods, however, there is considerable spatial and temporal variation in the availability of a seed source, substrates for seed germination, and in the light resource available for seedling growth and survival (Lieffers and Stadt 1994; Wright et al. 1998; Canham et al. 1999). Thus, the older stands studied by Peters et al. (2002) represented a small fraction of the conditions for white

Spatial patterns of cone serotiny in Pinus banksiana in relation to fire disturbance

Fire disturbance effects on tree species distribution and landscape pattern have been widely studied. However, the effects of differences among fire regimes on the spatial pattern of genetic variability within a tree species have received less attention. The objectives of this study were to examine (a) whether the marked gradient in serotiny in Pinus banksiana along its southern range limit is related to differences in fire regimes and (b) at what scale serotiny varies most strongly in P. banksiana in the US Midwest. P. banksiana in the 450,000 ha Pine Barrens area in northwestern Wisconsin, USA showed a marked broad scale pattern in serotiny. The percentage of serotinous trees was highest in the northeast (mean 83%, S.D. 13.5) and lowest in the southwest (mean 9%, S.D. 3.7). Historic fire regimes were inferred from pre-European settlement (mid-1800s) vegetation data. Serotiny was highest in pine forests that exhibited stand-replacing fires, and lowest in savannas where more frequent but less intense ground fires occurred. The data presented in this study suggest possible spatial control of genetic variability within a tree species by an ecological process (disturbance) at the landscape-scale.

Applying Logistic Regression to Determine Regeneration Risk to Stand Replacement Fire on the Kootenai National Forest, Montana

Abstract In 1994, fire managers on the Kootenai National Forest observed that wildfires had produced regeneration loss in some stands but not in others. They questioned what site characteristics and management activities were related to this loss. To address this question and to establish guidelines to “triage” stands and prioritize management efforts, we applied a logistic regression model to data from a set of regeneration stands (n = 135) located on the Libby, Rexford, and Three Rivers Ranger Districts. The occurrence of a stand replacement fire was modeled as a logistic function of Aspect, Habitat Type, Fuel Treatment, and logarithm of trees/ac (log_TPA), with R2 = 0.523 (P < 0.05). Odds ratios derived from logistic regression identified the descriptor characterizing regeneration stands “most at risk” for a stand replacement fire and provided a means to triage stands. Southwest and south aspects had the highest odds ratios (22 and 9) and largest coefficients of variation (3.07 and 2.22) for the Aspect variable. Western hemlock/queencup beadlilly (Tsuga heterophylla/Clintonia uniflora) and western red-cedar/queencup beadlilly (Thuja plicata/Clintonia uniflora), with respective odds ratios of 30 and 17, had the largest coefficients of variation (3.40 and 2.83) for the Habitat Type variable. For the Fuel Treatment variable, the “no fuel treatment” category had the highest odds ratio (11) and coefficient of variation (2.38). Stands with stand replacement fire had a mean log_TPA significantly lower than that of non-stand replacement fire stands (P < 0.001). Competition from understory vegetation may explain these findings. Bracken fern (Pteridium aquilinum), commonly found in cedar-hemlock stands and on southerly aspects, may outcompete tree seedlings and provide a fine-fuel hazard. West. J. Appl. For. 18(3):155–162.

Effects of litter addition on ectomycorrhizal associates of a lodgepole pine (Pinus contorta) stand in Yellowstone National Park.

Increasing soil nutrients through litter manipulation, pollution, or fertilization can adversely affect ectomycorrhizal (EM) communities by inhibiting fungal growth. In this study, we used molecular genetic methods to determine the effects of litter addition on the EM community of a Pinus contorta stand in Yellowstone National Park that regenerated after a stand-replacing fire. Two controls were used; in unmodified control plots nothing was added to the soil, and in perlite plots perlite, a chemically neutral substance, was added to maintain soil moisture and temperature at levels similar to those under litter. We found that (i) species richness did not change significantly following perlite addition (2.6 +/- 0.3 species/core in control plots, compared with 2.3 +/- 0.3 species/core in perlite plots) but decreased significantly (P < 0.05) following litter addition (1.8 +/- 0.3 species/core); (ii) EM infection was not affected by the addition of perlite but increased significantly (P < 0.001) in response to litter addition, and the increase occurred only in the upper soil layer, directly adjacent to the added litter; and (iii) Suillus granulatus, Wilcoxina mikolae, and agaricoid DD were the dominant organisms in controls, but the levels of W. mikolae and agaricoid DD decreased significantly in response to both perlite and litter addition. The relative levels of S. granulatus and a fourth fungus, Cortinariaceae species 2, increased significantly (P < 0.01 and P < 0.05, respectively) following litter addition. Thus, litter addition resulted in some negative effects that may be attributable to moisture-temperature relationships rather than to the increased nutrients associated with litter. Some species respond positively to litter addition, indicating that there are differences in their physiologies. Hence, changes in the EM community induced by litter accumulation also may affect ecosystem function.

Climatic controls on fire-induced sediment pulses in Yellowstone National Park and central Idaho: a long-term perspective

Fire management addressing postfire erosion and aquatic ecosystems tends to focus on short-term effects persisting up to about a decade after fire. A longer perspective is important in understanding natural variability in postfire erosion and sedimentation, the role of these processes in structuring habitat, and future expectations in light of a warming climate and environmental change. In cool high-elevation forests of northern Yellowstone National Park, stand ages indicate infrequent large stand-replacing fires. In warmer low-elevation forests of the Payette River region of Idaho, fire-scarred tree-rings record frequent low-severity fires before 1900; stand-replacing fires and resulting debris flows in recent decades are usually attributed to 20th-century fire suppression, grazing, and other land uses. In both areas, however, tree-ring records extend back only about 500 years. We use 14 C -dated geologic records to examine spatial and temporal patterns of fire-induced sedimentation and its relation to climate over the last 10 000 years. We review sedimentation processes in modern postfire events, which vary in magnitude and impact on stream systems depending on burn severity, basin geomorphology, and the timing and characteristics of postfire storms. Modern deposits also provide analogs for identification of fire-related deposits in alluvial fans. In Yellowstone, episodes of fire-induced sedimentation occurred at intervals of about 300–450 years during the last 3500 years, indicating a regime of infrequent high-severity fires. Millennial-scale variations in the fire-sedimentation record appear to relate to hemispheric-scale climatic change. Fire-related sedimentation is rare in Yellowstone during cooler episodes (e.g., the Little Ice Age ∼1200–1900 a.d.), probably because effectively wetter conditions prevented most fires from spreading. During some of the same cool periods, the Payette region experienced light surface fires and frequent, small pulses of fire-induced sediment. Between 900 and 1200 a.d., however, large fire-related debris flows occurred in both study areas, coincident with the Medieval Warm Period. During that time, drought may have limited grass growth in xeric Payette-region forests, restricting surface fire spread and allowing understory shrubs and trees to create ladder fuels. Although fire suppression and land-use effects are clearly involved in recent catastrophic fires in the Payette region, a warming climate and severe drought are probable contributors to major stand-replacing fires and postfire sedimentation, both past and present. Restoration and maintenance of conditions prior to European settlement may be unrealistic because of the potent influence of climate, and the incidence of severe fires will likely increase in both areas with future warming.

Processes and rates of sediment and wood accumulation in headwater streams of the Oregon Coast Range, USA

AbstractChannels that have been scoured to bedrock by debris flows provide unique opportunities to calculate the rate of sediment and wood accumulation in low‐order streams, to understand the temporal succession of channel morphology following disturbance, and to make inferences about processes associated with input and transport of sediment. Dendrochronology was used to estimate the time since the previous debris flow and the time since the last stand‐replacement fire in unlogged basins in the central Coast Range of Oregon. Debris flow activity increased 42 per cent above the background rate in the decades immediately following the last wildfire. Changes in wood and sediment storage were quantified for 13 streams that ranged from 4 to 144 years since the previous debris flow. The volume of wood and sediment in the channel, and the length of channel with exposed bedrock, were strongly correlated with the time since the previous debris flow. Wood increased the storage capacity of the channel and trapped the majority of the sediment in these steep headwater streams. In the absence of wood, channels that have been scoured to bedrock by a debris flow may lack the capacity to store sediment and could persist in a bedrock state for an extended period of time. With an adequate supply of wood, low‐order channels have the potential of storing large volumes of sediment in the interval between debris flows and can function as one of the dominant storage reservoirs for sediment in mountainous terrain. Copyright © 2003 John Wiley &amp; Sons, Ltd.

Re-introducing fire at the urban/wild-land interface: planning for success

The application of fire in the southern United States continues to increase in complexity due to urban sprawl, air quality issues and regulatory constraints. Many sites suffer from unnaturally high fuel accumulations dueto decades of fire exclusion. The loss of habitat to urbanization and successional changes resulting from the absence of fire increases the importance of restoring and maintaining those remaining acres. The wild-land/urban interface case study we discuss herein includes several fire-adapted plant communities ranging in required fire regime from frequent low-intensity fires to infrequent high-intensity stand replacement fires. This area has experienced extended fire-free periods and includes tightly packed homes in subdivisions developed with no consideration of the potential fOr wild-land fire. Additional smoke-sensitive areas include schools and heavily travelled highways. Such worst-case scenarios exponentially increase the challenges/risks facing fire managers. This case study thus illustrates many of the complex societal issues and technical challenges facing fire managers when planning and conducting restoration burns in the wild-land/urban interface. In fact, it reinforces the notion that, when burning in the wild-land/urban interface, executing the burn often requires less effort than the planning, co-operation and co-ordination necessary prior to ignition.