Uncertainty in managing forested landscapes arises from many sources, including complexities inherent in forest ecosystems
and their disturbance processes. However, gaining knowledge about forested ecosystems at the landscape level is often impeded
by limitations in collecting comprehensive, representative, as well as accurate data sets. Historical reference data sets
about past disturbances are also mostly lacking. In the case of ground fires, however, records of past fires can be obtained
by analyzing fire scars using dendrochronology. While the temporal series of disturbance can be determined, there is still
uncertainty about the spatial limits of individual forest surface fires. Here, we investigate how a patch-based method (fuzzy
set membership) and a boundary-based uncertainty method (boundary membership) can help determine the spatial uncertainty related
to forest fire events and their boundary locations. We compare these methods using fire scar data from ponderosa pine (Pinus ponderosa) and Douglas-fir (Pseudotsuga menziesii) sampled at 33 1-ha plots in a 1500-ha study area within the Stein River watershed (British Columbia). Patch-based fire maps,
using multiple constraints, were derived for years 1785–1937. We compared the resulting total fire event maps with the boundary-based
method, finding that depending on values chosen for the patch-based method, negative correlation was present (though very
modest: r = − 0.1, p ≤ 0.05) between some maps. However, significant positive correlation between maps (though again modest: r = 0.22, p ≤ 0.05) was found under the least constrained patch-based methods, suggesting that fire patches are counted more than once
in riparian zones. Our results suggest that these two methods provide complementary information about historical fire size
and spatial limits. Quantifying spatial uncertainty about fire size and fire boundary location using a boundary membership
method can contribute to not only understanding past fire regimes but also to providing better estimates of area burned. 相似文献
Parameters of fire regimes, including fire frequency, spatial extent of burned areas, fire severity, and season of fire occurrence, influence vegetation patterns over multiple scales. In this study, centuries-long patterns of fire events in a montane ponderosa pine – Douglas-fir forest landscape surrounding Cheesman Lake in central Colorado were reconstructed from fire-scarred trees and inferences from forest stand ages. We crossdated 153 fire-scarred trees from an approximately 4000 ha study area that recorded 77 total fire years from 1197 to the present. Spatial extent of burned areas during fire years varied from the scale of single trees or small clusters of trees to fires that burned across the entire landscape. Intervals between fire years varied from 1 to 29 years across the entire landscape to 3 to 58 years in one stand, to over 100 years in other stands. Large portions of the landscape did not record any fire for a 128 year-long period from 1723 to 1851. Fire severity varied from low-intensity surface fires to large-scale, stand-destroying fires, especially during the 1851 fire year but also possibly during other years. Fires occurred throughout tree growing seasons and both before and after growing seasons. These results suggest that the fire regime has varied considerably across the study area during the past several centuries. Since fires influence plant establishment and mortality on the landscape, these results further suggest that vegetation patterns changed at multiple scales during this period. The fire history from Cheesman Lake documents a greater range in fire behavior in ponderosa pine forests than generally has been found in previous studies. 相似文献
Climate and land-use change have led to disturbance regimes in many ecosystems without a historical analog, leading to uncertainty about how species adapted to past conditions will respond to novel post-disturbance landscapes.
Objectives
We examined habitat selection by spotted owls in a post-fire landscape. We tested whether selection or avoidance of severely burned areas could be explained by patch size or configuration, and whether variation in selection among individuals could be explained by differences in habitat availability.
Methods
We applied mixed-effects models to GPS data from 20 spotted owls in the Sierra Nevada, California, USA, with individual owls occupying home ranges spanning a broad range of post-fire conditions after the 2014 King Fire.
Results
Individual spotted owls whose home ranges experienced less severe fire (<?5% of home range severely burned) tended to select severely burned forest, but owls avoided severely burned forest when more of their home range was affected (~ 5–40%). Owls also tended to select severe fire patches that were smaller in size and more complex in shape, and rarely traveled?>?100-m into severe fire patches. Spotted owls avoided areas that had experienced post-fire salvage logging but the interpretation of this effect was nuanced. Owls also avoided areas that were classified as open and/or young forest prior to the fire.
Conclusions
Our results support the hypothesis that spotted owls are adapted to historical fire regimes characterized by small severe fire patches in this region. Shifts in disturbance regimes that produce novel landscape patterns characterized by large, homogeneous patches of high-severity fire may negatively affect this species.
In the southwestern U.S., wildland fire frequency and area burned have steadily increased in recent decades, a pattern attributable
to multiple ignition sources. To examine contributing landscape factors and patterns related to the occurrence of large (⩾20 ha
in extent) fires in the forested region of northern Arizona, we assembled a database of lightning- and human-caused fires
for the period 1 April to 30 September, 1986–2000. At the landscape scale, we used a weights-of-evidence approach to model
and map the probability of occurrence based on all fire types (n = 203), and lightning-caused fires alone (n = 136). In total, large fires burned 101,571 ha on our study area. Fires due to lightning were more frequent and extensive
than those caused by humans, although human-caused fires burned large areas during the period of our analysis. For all fires,
probability of occurrence was greatest in areas of high topographic roughness and lower road density. Ponderosa pine (Pinus ponderosa)-dominated forest vegetation and mean annual precipitation were less important predictors. Our modeling results indicate
that seasonal large fire events are a consequence of non-random patterns of occurrence, and that patterns generated by these
events may affect the regional fire regime more extensively than previously thought. Identifying the factors that influence
large fires will improve our ability to target resource protection efforts and manage fire risk at the landscape scale. 相似文献
Lack of quantitative observations of extent, frequency, and severity of large historical fires constrains awareness of departure of contemporary conditions from those that demonstrated resistance and resilience to frequent fire and recurring drought.
Objectives
Compare historical and contemporary fire and forest conditions for a dry forest landscape with few barriers to fire spread.
Methods
Quantify differences in (1) historical (1700–1918) and contemporary (1985–2015) fire extent, fire rotation, and stand-replacing fire and (2) historical (1914–1924) and contemporary (2012) forest structure and composition. Data include 85,750-ha tree-ring reconstruction of fire frequency and extent; >?375,000-ha timber inventory following >?78,900-ha fires in 1918; and remotely-sensed maps of contemporary fire effects and forest conditions.
Results
Historically, fires?>?20,000 ha occurred every 9.5 years; fire rotation was 14.9 years; seven fires?>?40,469 ha occurred during extreme drought (PDSI <?? 4.0); and stand-replacing fire occurred primarily in lodgepole (Pinus contorta var. murrayana). In contemporary fires, only 5% of the ecoregion burned in 30 years, and stand-replacing fire occurred primarily in ponderosa (Pinus ponderosa) and mixed-conifer. Historically, density of conifers?>?15 cm dbh exceeded 120 trees/ha on?<?5% of the area compared to 95% currently.
Conclusions
Frequent, large, low-severity fires historically maintained open-canopy ponderosa and mixed-conifer forests in which large fire- and drought-tolerant trees were prevalent. Stand-replacing patches in ponderosa and mixed-conifer were rare, even in fires >?40,469 ha (minimum size of contemporary “megafires”) during extreme drought. In this frequent-fire landscape, mixed-severity fire historically influenced lodgepole and adjacent forests. Lack of large, frequent, low-severity fires degrades contemporary forest ecosystems.
Assessing the long-term dynamics of mountain landscapes that are influenced by large-scale natural and anthropogenic disturbances
and a changing climate is a complex subject. In this study, a landscape-level ecological model was modified to this end. We
describe the structure and evaluation of the fire sub-model of the new landscape model LandClim, which was designed to simulate climate–fire–vegetation dynamics. We applied the model to an extended elevational gradient
in the Colorado Front Range to test its ability to simulate vegetation composition and the strongly varying fire regime along
the gradient. The simulated sequence of forest types along the gradient corresponded to the one observed, and the location
of ecotones lay within the range of observed values. The model captured the range of observed fire rotations and reproduced
realistic fire size distributions. Although the results are subject to considerable uncertainty, we conclude that LandClim can be used to explore the relative differences of fire regimes between strongly different climatic conditions. 相似文献
The structure of landscapes subject to patch-forming catastrophic disturbances, or disturbance landscapes, is controlled by the characteristics of the disturbance regime, including the distribution of disturbance sizes and intervals, and the rotation time. The primary landscape structure in disturbance landscapes is the structure of the mosaic of disturbance patches, which can be described by indices such as patch size and shape.The purpose of this research was to use a geographical information system-based spatial model (DISPATCH) to simulate the effects of the initial density of patches on the rate of response to alteration of a disturbance regime, the effects of global warming and cooling, and the effects of fragmentation and restoration, on the structure of a generalized temperate-zone forested disturbance landscape over a period of 400 yr.The simulations suggest that landscapes require 1/2 to 2 rotations of a new disturbance regime to adjust to that regime regardless of the size and interval distributions. Thus alterations that shorten rotations, as would be the case if global warming increases fire sizes and decreases fire intervals, produce a more rapid response than do alterations that lengthen rotations, such as cooling and fire suppression. Landscape with long rotations may be in perpetual disequilibrium with their disturbance regimes due to a mismatch between their adjustment rate and the rate of climatic change. Landscapes with similar rotation times may have different structures, because size and interval distributions independently affect landscape structure. The response of disturbance landscapes to changing disturbance regimes is governed by both the number and size of patch births. 相似文献
In fire-excluded forests across western North America, recent intense wildfire seasons starkly contrast with fire regimes of the past. The last 100 years mark a transition between pre-colonial and modern era fire regimes, providing crucial context for understanding future wildfire behavior.
Objectives
Using the greatest time depth of digitized fire events in Canada, we identify distinct phases of wildfire regimes from 1919 to 2019 by evaluating changes in mapped fire perimeters (>?20-ha) across the East Kootenay region (including the southern Rocky Mountain Trench), British Columbia.
Methods
We detect transitions in annual number of fires, burned area, and fire size; explore the role of lightning- and human-caused fires in driving these transitions; and quantify departures from historical fire frequency at the regional level.
Results
Relative to historical fire frequency, fire exclusion has created a significant fire deficit in active fire regimes, with a minimum of 1–10 fires missed across 46.4-percent of the landscape. Fire was active from 1919 to 1939 with frequent and large fire events, but the regime was already altered by a century of colonization. Fire activity decreased in 1940, coinciding with effective fire suppression influenced by a mild climatic period. In 2003, the combined effects of fire exclusion and accelerated climate change fueled a shift in fire regimes of various forest types, with increases in area burned and mean fire size driven by lightning.
Conclusions
The extent of fire regime disruption warrants significant management and policy attention to alter the current trajectory and facilitate better co-existence with wildfire throughout this century.
Short- and long-term patterns of net ecosystem carbon balance (NECB) for small, relatively uniform forest stands have been
examined in detail, but the same is not true for landscapes, especially those with heterogeneous disturbance histories. In
this paper, we explore the effect of two contrasting types of disturbances (i.e., fire and tree harvest) on landscape level
NECB by using an ecosystem process model that explicitly accounts for changes in carbon (C) stores as a function of disturbance
regimes. The latter were defined by the average disturbance interval, the regularity of the disturbance interval (i.e., random,
based on a Poisson frequency distribution, or regular), the amount of C removed by the disturbance (i.e., severity), and the
relative abundance of stands in the landscape with unique disturbance histories. We used the model to create over 300 hypothetical
landscapes, each with a different disturbance regime, by simulating up to 200 unique stand histories and averaging their total
C stores. Mean NECB and its year-to-year variability was computed by calculating the difference in mean total C stores from
one year to the next. Results indicated that landscape C stores were higher for random than for regular disturbance intervals,
and increased as the mean disturbance interval increased and as the disturbance severity decreased. For example, C storage
was reduced by 58% when the fire interval was shortened from 250 years to 100 years. Average landscape NECB was not significantly
different than zero for any of the simulated landscapes. Year-to-year variability in landscape NECB, however, was related
to the landscape disturbance regime; increasing with disturbance severity and frequency, and higher for random versus regular
disturbance intervals. We conclude that landscape C stores of forest systems can be predicted using the concept of disturbance
regimes, a result that may be a useful for adjusting estimates of C storage to broad scales that are solely based on physiological
processes. 相似文献
The complexity inherent in variable, or mixed-severity fire regimes makes quantitative characterization of important fire
regime attributes (e.g., proportion of landscape burned at different severities, size and distribution of stand-replacing
patches) difficult. As a result, there is ambiguity associated with the term ‘mixed-severity’. We address this ambiguity through
spatial analysis of two recent wildland fires in upper elevation mixed-conifer forests that occurred in an area with over
30 years of relatively freely-burning natural fires. We take advantage of robust estimates of fire severity and detailed spatial
datasets to investigate patterns and controls on stand-replacing patches within these fires. Stand-replacing patches made
up 15% of the total burned area between the two fires, which consisted of many small patches (<4 ha) and few large patches
(>60 ha). Smaller stand-replacing patches were generally associated with shrub-dominated (Arctostaphylos spp. and Ceanothus spp.) and pine-dominated vegetation types, while larger stand-replacing patches tended to occur in more shade-tolerant, fir-dominated
types. Additionally, in shrub-dominated types stand-replacing patches were often constrained to the underlying patch of vegetation,
which for the shrub type were smaller across the two fire areas than vegetation patches for all other dominant vegetation
types. For white and red fir forest types we found little evidence of vegetation patch constraint on the extent of stand-replacing
patches. The patch dynamics we identified can be used to inform management strategies for landscapes in similar forest types. 相似文献
The mechanistic, spatially-explicit fire succession model, Fire-BGC (a Fire BioGeoChemical succession model) was used to investigate long-term trends in landscape pattern under historical and future fire regimes and present and future climate regimes for two 46000 ha landscapes in Glacier National Park, Montana, USA. Fire-BGC has two spatial and temporal resolutions in the simulation architecture where ecological processes that act at a landscape level, such as fire, are simulated annually from information contained in spatial data layers, while stand-level processes such as photosynthesis, transpiration, and decomposition are simulated both daily and annually. Fire is spread across the landscape using the FARSITE fire growth model and subsequent fire effects are simulated at the stand-level. Fire-BGC was used to simulate changes in landscape pattern over 250 years under four scenarios: (1) complete fire exclusion under current climate, (2) historical wildfire occurrence and current climate, (3) complete fire exclusion under a possible future climate, (4) future wildfire occurrence and future climate. Simulated maps of dominant tree species, aboveground standing crop, leaf area index, and net primary productivity (NPP) were contrasted across scenarios using the metrics of patch density, edge density, evenness, contagion, and interspersion. Simulation results indicate that fire influences landscape pattern metrics more that climate alone by creating more diverse, fragmented, and disconnected landscapes. Fires were more frequent, larger, and more intense under a future climate regime. Landscape metrics showed different trends for the process-based NPP map when compared to the cover type map. It may be important to augment landscape analyses with process-based layers as well as structural and compositional layers. 相似文献
Fire regime characteristics of high-elevation forests on the North Rim of the Grand Canyon, Arizona, were reconstructed from fire scar analysis, remote sensing, tree age, and forest structure measurements, a first attempt at detailed reconstruction of the transition from surface to stand-replacing fire patterns in the Southwest. Tree densities and fire-/non-fire-initiated groups were highly mixed over the landscape, so distinct fire-created stands could not be delineated from satellite imagery or the oldest available aerial photos. Surface fires were common from 1700 to 1879 in the 4,400 ha site, especially on S and W aspects. Fire dates frequently coincided with fire dates measured at study sites at lower elevation, suggesting that pre-1880 fire sizes may have been very large. Large fires, those scarring 25% or more of the sample trees, were relatively infrequent, averaging 31 years between burns. Four of the five major regional fire years occurred in the 1700s, followed by a 94-year gap until 1879. Fires typically occurred in significantly dry years (Palmer Drought Stress Index), with severe drought in major regional fire years. Currently the forest is predominantly spruce-fir, mixed conifer, and aspen. In contrast, dendroecological reconstruction of past forest structure showed that the forest in 1880 was very open, corresponding closely with historical (1910) accounts of severe fires leaving partially denuded landscapes. Age structure and species composition were used to classify sampling points into fire-initiated and non-fire-initiated groups. Tree groups on nearly 60% of the plots were fire-initiated; the oldest such groups appeared to have originated after severe fires in 1782 or 1785. In 1880, all fire-initiated groups were less than 100 years old and nearly 25% of the groups were less than 20 years old. Non-fire-initiated groups were significantly older (oldest 262 years in 1880), dominated by ponderosa pine, Douglas-fir, or white fir, and occurred preferentially on S and W slopes. The mixed-severity fire regime, transitioning from lower-elevation surface fires to mixed surface and stand-replacing fire at higher elevations, appeared not to have been stable over the temporal and spatial scales of this study. Information about historical fire regime and forest structure is valuable for managers but the information is probably less specific and stable for high-elevation forests than for low-elevation ponderosa pine forests.This revised version was published online in May 2005 with corrections to the Cover Date. 相似文献
Fires and insect outbreaks are important agents of forest landscape change, but the classification and distribution of these combined processes remain unstudied aspects of forest disturbance regimes.
Objectives
We sought to map areas of land characterized by homogenous fire regime (HFR) attributes and by distinctive combinations of fire, bark beetles and defoliating insect outbreaks, and how their distribution might change should current climatic trends continue.
Methods
We used a 41-year history of mapped fires and forest insect outbreaks to classify HFRs and combined fire and insect disturbance regimes (HDRs). Spatially constrained cluster analysis of 2524 20-km grid cells used mean annual area burned, ignition Julian date, fire size and fire frequency to delineate HFR zones. Mean annual areas burned, affected by bark beetles, and affected by defoliators were used to delineate HDR zones. Random forests classification used climate associations of HDRs to project likely changes in their distribution.
Results
Eighteen HFR zones accounted for 30% of variance, compared to 27 HDR zones accounting for 59% of variance. Fire regime designation had low predictive power in explaining 23 homogenous insect outbreak regimes or the 27 HDRs. Climate change projections indicate a northward migration of current HDR zones. Conditions suitable for defoliator outbreaks are projected to increase, resulting in a projected increase in the total rate of forest disturbance.
Conclusions
When describing forest disturbance regimes, it is important to consider the combined and possibly interacting agents of tree mortality, which can result in emergent properties not predictable from any single agent.
The present study assesses the spatial distribution of selected land cover classes at two years (1975 and 2000) in a Mediterranean urban area (Athens, Greece) to test the hypothesis that land cover changes determine an increase in the sensitivity of landscape to forest fires on a regional scale. While urban and agricultural areas increased, although with different rates of growth, forests and semi-natural areas decreased in the study area. These changes are reflected in a significant increase of vegetation sensitivity to forest fires measured by the forest fire risk (FR) index developed in the framework of MEDALUS project. The cover classes which contributed the most to the increase of the FR index were crop mosaic, mixed agricultural-natural areas and discontinuous, low-density settlements. Results of the present study indicate that the transformation of the fringe landscape towards low-quality agricultural and pasture areas and fragmented forest patches is potentially detrimental for environmental quality and the ecological fragility of land. 相似文献
The relations between disturbance regime and landscape patterns have been developed from a theoretical perspective, but few studies have tested these relations when forces promoting opposing heterogeneity patterns are simultaneously operating on a landscape. This work provides quantitative evidence of these relations in areas dominated by human activity, showing that landscape heterogeneity decreases disturbance spread. In turn, disturbance introduces a source of landscape heterogeneity, but it is not enough to counterbalance the homogeneity trend due to agricultural abandonment. Land cover changes and wildfire occurrence (fires larger than 0.3 km2) have been monitored in the Tivissa municipality (208.4 km2) (Catalonia, NE Spain) from 1956 to 1993. Land cover maps were obtained from 1956, 1978 and 1993 and they were overlaid with fire occurrence maps obtained for the 1975–1995 period from 60 m resolution remote sensing images, which allow the identification of burned areas by sudden drops in Normalized Difference Vegetation Index (NDVI). Changes in landscape patterns in relation to fire regime have been analyzed considering several parameters: patch density, mean patch size, mean distance to the nearest neighbour of the same category, edge density, and the Shannon diversity index. In the 1956–1993 period there is a trend to increasing landscape homogenization due to the expansion of shrublands linked to a decrease in forest surface, and to the abandonment of agricultural lands. This trend, however, is not constant along all the period. Fires are more likely to occur in woody, homogenous areas, increasing landscape heterogeneity, as observed in the 1978–1993 period. This increase in heterogeneity does not counterbalance the general trend to landscape homogenization as a consequence of agricultural abandonment and the coalescence of natural vegetation patches.This revised version was published online in May 2005 with corrections to the Cover Date. 相似文献
The historical range of variability (HRV) has been suggested as a coarse filter approach to maintain ecosystem sustainability
and resiliency. The historical range of variability in forest age structure for the central eastern Cascade Range in Washington
State, USA was developed from historical fire return intervals and the manner in which fire acted as both cyclic and stochastic
processes. The proportions of seven forest structural stages calculated through these processes were applied to the area of
each forest series within the central eastern Cascades landscape. Early successional forest stages were more common in high
elevation forest than low elevation forest. The historical proportion of old growth and late successional forest varied from
38 to 63 percent of the forested landscape. These process-based estimates are consistent with those developed from forest
structural information. HRV is a valuable planning tool for ecosystem conservation purposes, but must be applied to real landscapes
with consideration of both temporal and spatial scale.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
In the interior Northwest, debate over restoring mixed-conifer forests after a century of fire exclusion is hampered by poor understanding of the pattern and causes of spatial variation in historical fire regimes.
Objectives
To identify the roles of topography, landscape structure, and forest type in driving spatial variation in historical fire regimes in mixed-conifer forests of central Oregon.
Methods
We used tree rings to reconstruct multicentury fire and forest histories at 105 plots over 10,393 ha. We classified fire regimes into four types and assessed whether they varied with topography, the location of fuel-limited pumice basins that inhibit fire spread, and an updated classification of forest type.
Results
We identified four fire-regime types and six forest types. Although surface fires were frequent and often extensive, severe fires were rare in all four types. Fire regimes varied with some aspects of topography (elevation), but not others (slope or aspect) and with the distribution of pumice basins. Fire regimes did not strictly co-vary with mixed-conifer forest types.
Conclusions
Our work reveals the persistent influence of landscape structure on spatial variation in historical fire regimes and can help inform discussions about appropriate restoration of fire-excluded forests in the interior Northwest. Where the goal is to restore historical fire regimes at landscape scales, managers may want to consider the influence of topoedaphic and vegetation patch types that could affect fire spread and ignition frequency.
Landscape Ecology - We undertook reconstructions of historical ponderosa pine forest structure and fire regimes across an entire landscape to expand understanding of spatial variability in forest... 相似文献
It is reasonable to assume that there is a relationship between the spatial distribution of forest fuels and fire hazards.
Therefore, if fire risk is to be included into numerical forest planning, the spatial distribution of risky and non-risky
forest stands should be taken into account. The present study combines a stand-level fire risk model and landscape level optimization
to solve forest planning problems in which the fire risk plays an important role. The key point of the method was to calculate
forest level fire resistance metrics from stand level indices and use these metrics as objective variables in numerical optimization.
This study shows that maximizing different landscape metrics produces very different landscape configurations with respect
to the spatial arrangement of resistant and risky stands. The landscapes obtained by maximizing different metrics were tested
with a fire spread simulator. These tests suggested that the mean fire resistance of the landscape, which is a non-spatial
metric, is the most important factor affecting the burned area. However, spatial landscape metrics that decrease the continuity
of fire resistance in the landscape can significantly improve the fire resistance of the landscape when used as additional
objective variables. 相似文献
