Low Burn Severity Research Articles

What drives European beech (Fagus sylvatica L.) mortality after forest fires of varying severity?

Predicting the timing and amount of tree mortality after a forest fire is of paramount importance for post-fire management decisions, such as salvage logging or reforestation. Such knowledge is particularly needed in mountainous regions where forest stands often serve as protection against natural hazards (e.g., snow avalanches, rockfalls, landslides). In this paper, we focus on the drivers and timing of mortality in fire-injured beech trees (Fagus sylvatica L.) in mountain regions. We studied beech forests in the southwestern European Alps, which burned between 1970 and 2012. The results show that beech trees, which lack fire-resistance traits, experience increased mortality within the first two decades post-fire with a timing and amount strongly related to the burn severity. Beech mortality is fast and ubiquitous in high severity sites, whereas small- (DBH <12cm) and intermediate-diameter (DBH 12–36cm) trees face a higher risk to die in moderate-severity sites. Large-diameter trees mostly survive, representing a crucial ecological legacy for beech regeneration. Mortality remains low and at a level similar to unburnt beech forests for low burn severity sites. Beech trees diameter, the presence of fungal infestation and elevation are the most significant drivers of mortality. The risk of beech to die increases toward higher elevation and is higher for small-diameter than for large-diameter trees. In case of secondary fungi infestation beech faces generally a higher risk to die. Interestingly, fungi that initiate post-fire tree mortality differ from fungi occurring after mechanical injury. From a management point of view, the insights about the controls of post-fire mortality provided by this study should help in planning post-fire silvicultural measures in montane beech forests.

Estimating mercury emissions resulting from wildfire in forests of the Western United States

Understanding the emissions of mercury (Hg) from wildfires is important for quantifying the global atmospheric Hg sources. Emissions of Hg from soils resulting from wildfires in the Western United States was estimated for the 2000 to 2013 period, and the potential emission of Hg from forest soils was assessed as a function of forest type and soil-heating. Wildfire released an annual average of 3100±1900kg-Hgy−1 for the years spanning 2000–2013 in the 11 states within the study area. This estimate is nearly 5-fold lower than previous estimates for the study region. Lower emission estimates are attributed to an inclusion of fire severity within burn perimeters. Within reported wildfire perimeters, the average distribution of low, moderate, and high severity burns was 52, 29, and 19% of the total area, respectively. Review of literature data suggests that that low severity burning does not result in soil heating, moderate severity fire results in shallow soil heating, and high severity fire results in relatively deep soil heating (<5cm). Using this approach, emission factors for high severity burns ranged from 58 to 640μg-Hgkg-fuel−1. In contrast, low severity burns have emission factors that are estimated to be only 18–34μg-Hgkg-fuel−1. In this estimate, wildfire is predicted to release 1–30gHgha−1 from Western United States forest soils while above ground fuels are projected to contribute an additional 0.9 to 7.8gHgha−1. Land cover types with low biomass (desert scrub) are projected to release less than 1gHgha−1. Following soil sources, fuel source contributions to total Hg emissions generally followed the order of duff>wood>foliage>litter>branches.

Fire severity mediates seedling recruitment patterns in slender mulga (Acacia aptaneura), a fire-sensitive Australian desert shrub with heat-stimulated germination

Members of the widespread arid Australian mulga (Acacia aneura) complex are fire-sensitive shrubs or small trees that can resprout epicormically following low-severity burning, but are readily killed by high-severity fire. The seeds of many species of mulga are stimulated to germinate by heat during burning, although post-fire regeneration rates are unpredictable. Here, we investigated whether variability in post-fire mulga recruitment relates to the relationship between fire severity and soil heating during fire, which may kill, leave unaffected, or stimulate the germination of buried seeds. This hypothesis was examined in central Australia on slender mulga (A. aptaneura), by experimentally investigating (a) seedling recruitment rates under different fire severity classes, (b) the germination and lethal temperature thresholds of seeds, (c) soil temperatures during fires of different severity classes and (d) the emergence depths of seedlings beneath high- and low-severity burnt plants. We found that post-fire recruitment was significantly lower beneath low-severity burnt and unburnt plants than high-severity burnt plants. This result was explained by the finding that maximum germinability of mulga seeds occurs after heating to between 80 and 100 °C, and that these temperatures are not achieved in unburnt patches or low-severity burns at depths where the majority of the seed bank is known to occur. Despite the increased regeneration observed after high-severity fire, post-fire recruitment was highly variable between sites, independent of fire severity. This indicates that while heat-stimulated germination may confer on mulga a risk-spreading strategy to a range of fire severities, post-burn recruitment may not always offset high adult death rates following high-severity fire.

Remote sensing approach to detect post-fire vegetation regrowth in Siberian boreal larch forest

Remote sensing with time series data offers considerable potential in the trajectory of post forest fire dynamics beyond the current monitoring of structural attributes that are displayed in the post-fire area. Many studies have addressed this topic by using time series remote sensing indices; however, this approach has sometimes been demonstrated as an unrealistic and biased representation of the post-fire forest patterns due to the saturation issues of vegetation indices. These saturation issues then lead to an underestimation of the forest successional stages and an overestimation of the forest recovery rate. This paper aims to develop a framework for trajectory of the post-fire forest patterns in the Siberian boreal larch forest (Larix sibirica) with the synergistic use of different remote sensing based vegetation-cover indicators derived from the Landsat time series and the WorldView-2 images. A time-series of the forest recovery index (FRI) and fractional vegetation cover (FVC) has been analyzed to estimate the rates of forest regeneration and vegetation recovery across different burn severity levels in the Siberian larch forest. The results showed that the FRI method can be used to observe the regrowth of the larch forest from the tenth year after the fire overlapping with the period of significant increase in the sapling stem volume. The post-fire larch forest canopy can fully recover to the pre-fire condition with respect to the magnitude of the FRI values after 30–47 years where the highest regeneration rate was observed in the moderate burn severity areas followed by the low and high burn severity. On the other hand, the FVC method was positively correlated with burn severity and more sensitive for evaluating the early stages of the forest succession in which the FVC dramatically increases after 5–6 years after the fire. The significant growth of FVC was accentuated by the maximum emergence of the sapling density as well as the rapid growth of herbaceous plants, grasses, shrubs, and shade-intolerant trees immediately after the fire, which could not be evaluated using the FRI. Both time series of the FRI and the FVC are valuable tools for determining the dominant stages of the post-fire larch forest succession in order to understand the relationships between fire disturbance and natural cycles of the boreal larch forest.

Carbon loss during the early decomposition stages of tree stumps in a post-wildfire Spanish black pine forest

Post-fire carbon released by the decomposition process of tree stumps in a Spanish black pine (Pinus nigra Arn. ssp. salzmannii) forest of the Cuenca Mountain range (Spain) was assessed during the first three years after felling fire-killed trees. Carbon loss was estimated at high- and low-burn severity sites by two different ways: (1) via wood mass loss (indirect method); and (2) via in situ CO2 efflux measurements (Rstump, direct method). By the indirect method, different aboveground wood decomposition parameters were estimated, i.e. decay rate (ka) and half life period (t0,5). By the direct method, multiple regression models related stump diameter and temperature to instantaneous Rstump. The results indicate that C loss depended on post-fire environmental conditions and woody substrate quality (i.e. stump size). Both methods showed similar C release patterns, with higher values obtained by the direct method for all study sites and tree stump sizes, likely because a portion of the CO2 originating in the belowground part of stump was diffused through the decomposed aboveground part. Using the defined Rstump models for ecosystem upscaling, the annual C loss of the study sites ranged from 0.08±0.01 to 1.33±0.06MgCha−1year−1. Thereby, stumps could be considered hot spots of CO2 production during their early stages of decomposition, which particularly at post-fire managed areas, with large numbers are left to decompose, can represent a significant and poorly studied part of the total ecosystem respiration.

Vegetation Response to Burn Severity, Native Grass Seeding, and Salvage Logging

AbstractAs the size and extent of wildfires has increased in recent decades, so has the cost and extent of post-fire management, including seeding and salvage logging. However, we know little about how burn severity, salvage logging, and post-fire seeding interact to influence vegetation recovery long-term. We sampled understory plant species richness, diversity, and canopy cover one to six years post fire (2006 to 2009, and 2011) on 72 permanent plots selected in a stratified random sample to define post-fire vegetation response to burn severity, post-fire seeding with native grasses, and salvage logging on the 2005 School Fire in eastern Washington. Understory vegetation responded rapidly post fire due, in part, to ample low intensity rainfall events in the first post-fire growing season. Vegetation was more diverse with greater plant species richness and diversity (Shannon-Wiener index) in low and moderate burn severity plots in 2006 (species richness 18; diversity 2.3) compared to high burn severity plots (species richness 10; diversity 1.8), with species richness on the high severity plots reaching 19 in the sixth post-fire year, similar to the initial values on the low and moderate burn severity plots. Plants that commonly resprout from rhizomes, bulbs, and other surviving belowground sources were abundant post fire, while those establishing from off-site seed sources, including non-native species, were present but not abundant. Plots seeded with native grass post fire and not salvage logged had the highest canopy cover of graminoid species: more than 30 % six years after the fire (in 2011), with low forb (15 %) and shrub (1 %) canopy cover and species richness. For comparison, high severity plots that were not seeded and not salvage logged had 3 % graminoid cover, 14 % forb cover, and 26 % shrub cover. Plots that had been salvage logged from one to three years after the fire produced less canopy cover of shrubs and forbs, but three times more canopy cover of graminoids on the high burn severity plots by 2011. High severity plots that were salvage logged and not seeded with native grasses had the lowest species richness, diversity, and cover. Very few non-native species were found, regardless of salvage logging and seeding. Rapid post-fire growth dominated by native plants of high diversity suggests that this forest’s vegetation and soils are highly resilient to disturbance. Overall, burn severity and post-fire seeding with native grasses were more influential than salvage logging on understory plant abundance one to six years after fire.

Impact of thermal shock on forest soils affected by fires of different severity and recurrence

Thermal treatments in the laboratory were conducted using &lt;/span&gt;&lt;span style="font-size: small;"&gt;unburned and burned samples of two soils affected by low- or high severity fires&lt;/span&gt;&lt;span style="font-size: small;"&gt; in order to study their impact on forests ecosystems with different fire regimes (severity, recurrence). Soils samples were heated in a furnace for 15 minutes at &lt;/span&gt;&lt;span style="font-size: small;"&gt;50 ºC, 75 ºC, 100 ºC, 125 ºC, 150 ºC, 175 ºC, 200 ºC and 300 ºC to simulate different fire intensities; the process was repeated after a 1 month incubation of the burned, rewetted samples in order to simulate fire recurrence. The soil temperature was measured with thermocouples at the surface and 1 cm depth. The maximum temperature reached (Tmax) and the amount of heat supplied to the samples (degree-hour, DH) were calculated from the temperature-time curves. &lt;/span&gt;&lt;span style="font-size: small;"&gt;A total of 128 temperature-time curves (4 soil field samples x 8 heating temperatures x 2 depths x 2 successive heat treatments) were analyzed and the estimation of several soil physical and chemical properties (color, moisture content, pH, total C, total N, soluble C) was carried out in the different soil treatments. H&lt;/span&gt;&lt;span style="font-size: small;"&gt;igh-severity burning provoked significant changes on these physical and chemical properties, whereas slight modifications or even no changes were due to low-severity burning or soil heating under laboratory conditions. The thermal properties exhibited a higher sensitivity for the detection of the fire regime impact than the physical and chemical properties. The results showed that the &lt;/span&gt;&lt;span style="font-size: small;"&gt;temperature-time curves and derived parameters (slope, Tmax, DH) can be successfully used to quantify the impact of thermal shocks at low and high temperatures and to evaluate the effect of fire/heating recurrence on forests ecosystems.

Burn severity alters peatland moss water availability: implications for post‐fire recovery

AbstractWildfire is the largest disturbance affecting northern peatlands; however, little is known about how burn severity (organic soil depth of burn) alters post‐fire hydrological conditions that control the recovery of keystone peatland mosses (i.e. Sphagnum). For this reason, we assessed the impact of burn severity on moss water availability by measuring soil tension (Ψ) and surface volumetric moisture content (θ) in burned and unburned portions of a peatland complex 2 years after fire. We found that both high and low burn severity decreased post‐fire water availability by altering peat hydrophysical properties (moisture retention and water repellency). Locations covered by Sphagnum fuscum prior to fire exhibited a decreasing post‐fire water availability with an increasing burn severity. In contrast, the lowest water availability (Ψ &gt; 400 cm, θ &lt; 0·02) was observed in feather mosses that underwent low burn severity (residual branches identifiable). Deep burning (&gt;0·20 m) in peatland margins and burn depths &gt;0·05 m in the middle of the peatland exhibited the highest water availability (Ψ &lt; 60 cm). Locations with low surface θ and high Ψ, notably feather mosses undergoing low burn severity, exhibited minimal moss recolonization. Such areas dominate post‐fire surface cover (~40%) within late successional (mature) peatlands or peatlands located in dry hydrological settings. We argue that such environments are under‐represented in conceptual models of post‐fire recovery. A new conceptual model is proposed in which (1) deep burning is counterbalanced by rapid recolonization and (2) pre‐fire species interact with burn severity to produce substantial lags in post‐fire moss recovery. Copyright © 2015 John Wiley &amp; Sons, Ltd.

Mapping burn severity in a disease-impacted forest landscape using Landsat and MASTER imagery

Global environmental change has increased forest vulnerability to the occurrence of interacting disturbances, including wildfires and invasive diseases. Mapping post-fire burn severity in a disease-affected forest often faces challenges because burned and infested trees may exhibit a high similarity in spectral reflectance. In this study, we combined (pre- and post-fire) Landsat imagery and (post-fire) high-spectral resolution airborne MASTER data [MODIS (moderate resolution imaging spectroradiometer)/ASTER (advanced spaceborne thermal emission and reflection radiometer)] to map burn severity in a California coastal forest environment, where a non-native forest disease sudden oak death (SOD) was causing substantial tree mortality. Results showed that the use of Landsat plus MASTER bundle performed better than using the individual sensors in most of the evaluated forest strata from ground to canopy layers (i.e., substrate, shrubs, intermediate-sized trees, dominant trees and average), with the best model performance achieved at the dominant tree layer. The mid to thermal infrared spectral bands (3.0–12.5μm) from MASTER were found to augment Landsat’s visible to shortwave infrared bands in burn severity assessment. We also found that infested and uninfested forests similarly experienced moderate to high degrees of burns where CBI (composite burn index) values were higher than 1. However, differences occurred in the regions with low burn severity (CBI values lower than 1), where uninfested stands revealed a much lower burn effect than that in infested stands, possibly due to their higher resilience to small fire disturbances as a result of higher leaf water content.

Validation of the German version of the Burn Specific Health Scale-Brief (BSHS-B)

BackgroundThe Burn Specific Health Scale-Brief (BSHS-B) is recognized as a valid self-rating scale to evaluate quality of life after burn. AimTo validate the translated German version of the BSHS-B. MethodOne hundred and forty one burn survivors (65.2% men) with a mean age of 49.62 years (SD=15.16) and a mean duration after burn of 45.01 months (SD=26.18) answered the BSHS-B. Factor structure was tested by using confirmatory factor analysis, reliability (internal consistency) of the scales was determined by means of Cronbach's α. Construct validity was explored through correlations between the BSHS-B and the Short-Form 8 Health Survey (SF-8). In addition, the know-groups technique was used to determine to which degree the BSHS-B discriminates between patients with low and high burn severity based on the abbreviated burn severity index (ABSI). The Hospital Anxiety and Depression Scale (HADS) was used to examine criterion validity. ResultsThe nine BSHS-B subscales showed good internal consistency. A second-order confirmatory factor analysis revealed the following main components: (1) Affect and Relationship, (2) Function and (3) Skin Involvement. The second-order factors were positively correlated with the SF-8 and negatively correlated with symptoms of anxiety and depression. Patients with low ABSI scored higher on all three BSHS-B domains than those with high ABSI. ConclusionsThe results indicate good psychometric properties of the German BSHS-B. Further studies are needed to investigate the utility of the questionnaire in clinical routine practice, evaluation of burn management programs, and burn-specific research.

The effects of burn entry and burn severity on ponderosa pine and mixed conifer forests in Grand Canyon National Park

Over a century of fire exclusion in frequent-fire ponderosa pine and dry mixed conifer forests has resulted in increased tree densities, heavy surface fuel accumulations and an increase in late successional, fire-intolerant trees. Grand Canyon National Park uses prescribed fires and wildfires to reduce fire hazard and restore ecosystem processes. Research is needed to determine post-fire vegetation response thus enabling future forest succession predictions. Our study focussed on the effects of burn entry and burn severity on species composition and regeneration in two forest types: ponderosa pine with white fir encroachment and dry mixed conifer. We found no difference in tree composition and structure in a single, low-severity burn compared with unburned areas in the white fir encroachment forest type. We found no white fir seedlings or saplings in a second-entry, low-severity burn in the white fir encroachment forest type. Second-entry burns were effective in reducing white fir densities in the white fir encroachment forest type. There was significant aspen regeneration following high-severity fire in the dry mixed conifer forest type. This research suggests that repeated entries and an increase in burn severity may be necessary for prescribed fire or wildfire to be effective in meeting management objectives.

Clearcutting and high severity wildfire have comparable effects on growth of direct-seeded interior Douglas-fir

The degree to which harvesting can achieve comparable beneficial effects to wildfire on seedling establishment is a key factor in understanding regeneration dynamics in dry interior forest ecosystems. We compared the capacity of harvesting versus wildfire to support establishment of directly-seeded interior Douglas-fir over a three-year period in the interior Douglas-fir biogeoclimatic zone of British Columbia. The mixed-severity McLure Fire of August 2003 affected over 26,000 hectares in the central British Columbia, Canada. Within the fire-affected area, we assessed growth performance in five disturbance types: High Severity Burn, Low Severity Burn, Clearcut, Screefed Clearcut, and Undisturbed Forest. Seedlings in the High Severity Burn had the significantly greater shoot biomass and root biomass than those in the Low Severity Burn and Undisturbed Forest in the first year. Additionally, seedlings in the High Severity Burn had significantly higher foliar N and P content than those in both clearcut treatments in year one. Foliar nitrogen concentrations remained above critical deficiency levels (1.4%) in both clearcut treatments and the High Severity Burn treatment in all three years. Overall, seedling growth performance in Screefed Clearcut was the most comparable with High Severity Burn treatment, indicating the potential for harvesting with site preparation to produce comparable effects to wildfire on aspects of seedling establishment, particularly growth and nutrition.

Legacy effects of fire size and severity on forest regeneration, recruitment, and wildlife activity in aspen forests

Human activities and climate change are increasing the size and severity of wildfires globally, creating a need for research that links changes in fire regimes with community-level responses. The objective of this study was to understand how variability in fire regimes influences forest regeneration and recruitment patterns and wildlife activity at large temporal and spatial scales. Across 25 fires in five National Forests (Uinta-Wasatch-Cache NF, Ashley NF, Fishlake NF, Dixie NF, and Manti-La Sal NF) in the state of Utah, we examined aspen regeneration and recruitment levels, and wildlife and livestock fecal group counts along belt transects that spanned gradients of fire size and severity. Forest cover change was assessed by comparing pre-fire and post-fire satellite images. The fires dated from 1992 to 2002 and were at least 10years old when this study was conducted. Fire size and severity were positively related to aspen regeneration (density of saplings) and recruitment (saplings>2m in height). There was a significant fire size and severity interaction effect on aspen regeneration, such that the positive influence of fire size increased with greater fire severity (R2=0.40, P<0.001). Change in the extent of aspen cover was not correlated with fire size. Deer and cattle became more dispersed with increasing fire size and severity, but elk activity showed no difference. Deer preferred low severity burn patches in smaller fires, but appeared to avoid low severity patches as fires became larger. Our results suggest that fire size and severity are important ecological filters that can interact to affect forest development and the distribution and abundance of large herbivores. Effective management of forest systems in response to altered fire regimes will require an understanding of the legacy effects of fire size and severity at the landscape scale.

Susceptibility of burned black spruce (Picea mariana) forests to non-native plant invasions in interior Alaska

As climate rapidly warms at high-latitudes, the boreal forest faces the simultaneous threats of increasing invasive plant abundances and increasing area burned by wildfire. Highly flammable and widespread black spruce (Picea mariana) forest represents a boreal habitat that may be increasingly susceptible to non-native plant invasion. This study assess the role of burn severity, site moisture and time elapsed since burning in determining the invisibility of black spruce forests. We conducted field surveys for presence of non-native plants at 99 burned black spruce forest sites burned in 2004 in three regions of interior Alaska that spanned a gradient of burn severities and site moisture levels, and a chronosequence of sites in a single region that had burned in 1987, 1994, and 1999. We also conducted a greenhouse experiment where we grew invasive plants in vegetation and soil cores taken from a subset of these sites. In both our field survey and the greenhouse experiment, regional differences in soils and vegetation between burn complexes outweighed local burn severity or site moisture in determining the invasibility of burned black spruce sites. In the greenhouse experiments using cores from the 2004 burns, we found that the invasive focal species grew better in cores with soil and vegetation properties characteristic of low severity burns. Invasive plant growth in the greenhouse was greater in cores from the chronosequence burns with higher soil water holding capacity or lower native vascular biomass. We concluded that there are differences in susceptibility to non-native plant invasions between different regions of boreal Alaska based on native species regeneration. Re-establishment of native ground cover vegetation, including rapidly colonizing bryophytes, appear to offer burned areas a level of resistance to invasive plant establishment.

Geographic Analysis of Burn Severity for the 2013 California Rim Fire

Analysis of Landsat imagery was applied to classify burn severity within the 2013 Rim Fire area using the relative difference normalized burn ratio (RdNBR). Results showed 53,220 ha in the High Burn Severity (HBS) class and another 34,214 ha in the Moderate Burn Severity (MBS) class. Within Yosemite National Park, 12,084 ha were detected by RdNBR analysis in the HBS class and another 11,089 ha in the MBS class. The most typical ecosystem habitat detected within the HBS class was Ponderosa pine—Mixed Conifer forest, between the elevations of 1000 and 2000 meters or on slopes between 5 and 30 percent. Most of the HBS areas were located in areas where high levels of pre-fire fuels were quantified by 2013 Landsat vegetation index (NDVI) values between 500 and 800. The Low Burn Severity (LBS) class covered a higher fraction of areas where the duration since last fire (YSF) was less than 25 years, compared to the HBS class, which covered a higher fraction of areas where the YSF was greater than 60 years.

Polarimetric Properties of Burned Forest Areas at C- and L-Band

Fully polarimetric C- and L-band synthetic aperture radar (SAR) data have been investigated to determine the relationship between polarimetric target decomposition components and forest burn severity over two sites located in a Mediterranean environment. The dependence of the polarimetric decomposition metrics on SAR acquisition geometry and environmental conditions was also analyzed at C-band. Multiple linear regression models with interactions (i.e., the incidence angle was included as a predictor variable and its interaction with the radar metrics was accounted for as a multiplicative effect) were used to quantify burn severity retrieval accuracy. According to our experiment, we found that for steep SAR acquisition geometries C-band polarimetric components related to surface scattering mechanisms had increased sensitivity to burn severity levels, while for datasets acquired with more grazing geometries the polarimetric components related to volume scattering and dihedral scattering mechanisms were more correlated with burn severity levels. At L-band only volume and dihedral scattering related decomposition components provided significant relationships with burn severity levels. Relatively low burn severity estimation errors (less than 20% of burn severity range) were obtained for all datasets, with L-band data presenting the highest sensitivity to fire effects. Using a single regression model provided sufficient accuracy for burn severity estimation when taking into account the local incidence angle. The use of fully polarimetric data improved the estimation accuracy of forest burn severity with respect to backscatter intensities by a small margin for our study sites. However, since backscatter intensity metrics already provide high retrieval accuracies, whatever improvement was bound to be low.

Post-fire tree recruitment of a boreal larch forest in Northeast China

Boreal larch forests in eastern Siberia contain about half of the carbon accumulated in Eurasian forest communities, and fire is an important disturbance in this area, contributing to changes in forest composition and breaking the original succession trajectory. Assessing burn severity and environmental controls on post-fire larch recruitment is critical for understanding long-term effects of fire disturbance on forest succession in this region. A mega-fire that burned 8700ha in the year 2000 in the Great Xing’ an Mountains provided an opportunity to study the effects of mixed-severity fire disturbance in larch forests. We sampled tree recruitment in 83 burned sites to address the question of how burn severity and site environment interact to influence the species composition and density of post-fire tree recruitment, and hence the successional trajectory of forest. We explored the hypothesis that the larch forest was more likely to replace itself rapidly (“self-replacement succession”) in areas of low-severity burn, but was more likely to be replaced by an early-seral community of broadleaf trees (“relay succession”) in areas of high-severity burn. Our analysis showed that post-fire conifer and broadleaf recruit densities were both negatively related to burn severity and understory cover. Environmental conditions (e.g. elevation, slope, aspect) had weaker influences than burn severity on post-fire tree densities, but played a stronger role in determining the relative proportion of conifer recruits. Broadleaf trees recruited abundantly in low-severity burns in upland areas, even though they were absent from most of the pre-fire sites. In contrast, coniferous trees recruited more abundantly in low-severity burns in valley bottom areas. The comparison of pre- and post-fire tree composition in the burned patches indicated that self-replacement succession was likely to occur in valley bottom areas that burned with low severity. Burned upland areas are more likely to experience an alternative, broadleaf-dominated trajectory of relay succession. The increase in the severity and frequency of fires due to climate warming may prompt shifts from a larch dominated forest to an increasingly birch dominated landscape, substantially altering landscape dynamics and ecosystem services.

Pre-wildfire management treatments interact with fire severity to have lasting effects on post-wildfire vegetation response

Land managers are routinely applying fuel reduction treatments to mitigate the risk of severe, stand-replacing fire in ponderosa pine communities of the southwestern US. When these treatments are burned by wildfire they generally reduce fire severity, but less is known about how they influence post-wildfire vegetation recovery, as compared to pre-fire untreated areas. We re-measured existing plots on the 2002 Rodeo–Chediski Fire 8years after the wildfire to track plant community and exotic species response, as well as patterns of pine regeneration. We compared areas that experienced high- and low-severity burning, and also examined how pre-fire treatment (cutting in an uneven-aged harvesting system with prescribed fire) modified vegetation response. We detected persistent differences between low- and high-severity areas for nearly all variables measured. In high-severity areas overall understory plant cover was 40.6%, nearly three times that observed in low-severity areas; shrub cover was 18.4%, four and a half times greater than that observed in low-severity areas. We also detected significantly higher exotic forb cover in high-severity areas, although overall exotic response was generally quite low (<2%). Although this represents a slight decrease in exotic cover since the initial 2004/2005 measurements, the frequency of several exotic species did increase through time (particularly Tragopogon dubius and Verbascum thapsus). Pre-fire treatment resulted in significantly higher pine regeneration frequency in treated versus untreated areas. Within low severity areas, mean pine regeneration frequency was 0.17 in pre-fire untreated areas versus 0.06 in areas that were not treated before the fire. Within high severity burned areas, mean pine regeneration frequency was 0.67 in pre-fire treated areas, but was only 0.19 in pre-fire untreated areas. This treatment effect in high-severity areas may be linked to reduction in the overall patch size of high burn severity in pre-fire treated areas, which resulted in a more heterogeneous mixture of low and moderate severity burning in the neighborhood. This pattern decreased distance to seed source, which likely facilitated the more frequent pine regeneration observed. In addition to the well-documented benefits of fuel reduction treatments in reducing subsequent fire severity, these data suggest that even where treated areas do burn severely the size of severely burned patches is limited in extent, which is likely to have important ramifications for future reforestation and retention of foundation species.

Ectomycorrhizal fungal community assembly on regenerating Douglas-fir after wildfire and clearcut harvesting

Wildfire severity in forests is projected to increase with warming and drying conditions associated with climate change. Our objective was to determine the impact of wildfire and clearcutting severity on the ectomycorrhizal fungal (EMF) community of Douglas-fir seedlings in the dry forests of interior British Columbia, Canada. We located our study within and surrounding the area of the McLure fire (August 2003). We hypothesized that disturbance would affect EMF community assembly due to reductions in fungal inoculum. Five treatments representing a range of disturbance severities were compared: high severity burn, low severity burn, screefed clearcut (manual removal of forest floor), clearcut, and undisturbed forest. EMF communities in the undisturbed forest were more complex than those in all disturbance treatments. However, aspects of community assembly varied with disturbance type, where the burn treatments had the simplest communities. After 4 months, regenerating seedlings in the burn treatments had the lowest colonization, but seedlings in all treatments were fully colonized within 1 year. EMF communities were similar among the four disturbance types, largely due to dominance of Wilcoxina throughout the study period. However, forest floor retention influenced community assembly as the EMF in the clearcut treatment, where forest floor was retained, had levels of diversity and richness comparable to the undisturbed forest. Overall, the results suggest that increasing forest floor disturbance can alter EMF community assembly in the first year of regeneration. A correlation between poorly colonized seedlings and seedling productivity also suggests a role for productivity in influencing community assembly.

Assessing Double Counting of Carbon Emissions Between Forest Land-Cover Change and Forest Wildfires: A Case Study in the United States, 1992–2006

The relative contributions of double counting of carbon emissions between forest-to-nonforest cover change (FNCC) and forest wildfires are an unknown in estimating net forest carbon exchanges at large scales. This study employed land-cover change maps and forest fire data in the four representative states (Arkansas, California, Minnesota, and Washington) of the US for the period from 1992 to 2006 to evaluate forest carbon double counting effects based on land-cover change map, forest fire data, and USDA Forest Service Forest Inventory and Analysis data. The analyses were conducted at the county level and tallied to state level. Although the effects were small in the two eastern states because of small burned areas and low burn severity, substantial effects were found in the two western states. Carbon double counting was about 10 TgC (teragram 10 12 ) in California and 6 TgC in Washington for the period 1992‐2006 (at rates of 0.7 and 0.4 TgC per year), or 21.9 and 7.6% relative to total forest carbon emissions through FNCC in the two states, respectively. The effects were 0.2 and 0.1% in Arkansas and Minnesota, respectively. Variation in double counting effects within the states was also much higher in the western states compared with the eastern states. Our results suggested a general pattern that rates and amounts of double counting in forest carbon emissions between FNCC and fires were more evident and substantially different on a west‐east dimension than that on a north‐south dimension across the conterminous US during the study period.