Heterogeneity in fire severity within early season and late season prescribed burns in a mixed-conifer forest

2006 ◽  
Vol 15 (1) ◽  
pp. 37 ◽  
Author(s):  
Eric E. Knapp ◽  
Jon E. Keeley
Keyword(s):  
Sierra Nevada ◽  
Prescribed Burning ◽  
Fire Severity ◽  
Basal Area ◽  
Conifer Forest ◽  
Fuel Loading ◽  
Early Season ◽  
Late Season ◽  
Fuel Loads ◽  
In Fire

Structural heterogeneity in forests of the Sierra Nevada was historically produced through variation in fire regimes and local environmental factors. The amount of heterogeneity that prescription burning can achieve might now be more limited owing to high fuel loads and increased fuel continuity. Topography, woody fuel loading, and vegetative composition were quantified in plots within replicated early and late season burn units. Two indices of fire severity were evaluated in the same plots after the burns. Scorch height ranged from 2.8 to 25.4 m in early season plots and 3.1 to 38.5 m in late season plots, whereas percentage of ground surface burned ranged from 24 to 96% in early season plots and from 47 to 100% in late season plots. Scorch height was greatest in areas with steeper slopes, higher basal area of live trees, high percentage of basal area composed of pine, and more small woody fuel. Percentage of area burned was greatest in areas with less bare ground and rock cover (more fuel continuity), steeper slopes, and units burned in the fall (lower fuel moisture). Thus topographic and biotic factors still contribute to the abundant heterogeneity in fire severity with prescribed burning, even under the current high fuel loading conditions. Burning areas with high fuel loads in early season when fuels are moister may lead to patterns of heterogeneity in fire effects that more closely approximate the expected patchiness of historical fires.

Role of burning season on initial understory vegetation response to prescribed fire in a mixed conifer forest

2007 ◽  
Vol 37 (1) ◽  
pp. 11-22 ◽  
Author(s):  
Eric E Knapp ◽  
Dylan W Schwilk ◽  
Jeffrey M Kane ◽  
Jon E Keeley
Keyword(s):  
Prescribed Burning ◽  
Understory Vegetation ◽  
Fire Intensity ◽  
Conifer Forest ◽  
Mixed Conifer ◽  
Fuel Loading ◽  
Significant Drop ◽  
Early Season ◽  
Late Season ◽  
Mixed Conifer Forest

Although the majority of fires in the western United States historically occurred during the late summer or early fall when fuels were dry and plants were dormant or nearly so, early-season prescribed burns are often ignited when fuels are still moist and plants are actively growing. The purpose of this study was to determine if burn season influences postfire vegetation recovery. Replicated early-season burn, late-season burn, and unburned control units were established in a mixed conifer forest, and understory vegetation was evaluated before and after treatment. Vegetation generally recovered rapidly after prescribed burning. However, late-season burns resulted in a temporary but significant drop in cover and a decline in species richness at the 1 m2 scale in the following year. For two of the several taxa that were negatively affected by burning, the reduction in frequency was greater after late-season than early-season burns. Early-season burns may have moderated the effect of fire by consuming less fuel and lessening the amount of soil heating. Our results suggest that, when burned under high fuel loading conditions, many plant species respond more strongly to differences in fire intensity and severity than to timing of the burn relative to stage of plant growth.

scholarly journals Opportunities for winter prescribed burning in mixed conifer plantations of the Sierra Nevada

Fire Ecology ◽  
2021 ◽  
Vol 17 (1) ◽  
Author(s):  
Robert A. York ◽  
Jacob Levine ◽  
Kane Russell ◽  
Joseph Restaino
Keyword(s):  
Sierra Nevada ◽  
Pinus Ponderosa ◽  
Prescribed Burning ◽  
Winter Season ◽  
Basal Area ◽  
Weather Conditions ◽  
Shrub Cover ◽  
Mixed Conifer ◽  
Planted Forests ◽  
Conifer Plantations

Abstract Background Young, planted forests are particularly vulnerable to wildfire. High severity effects in planted forests translate to the loss of previous reforestation investments and the loss of future ecosystem service gains. We conducted prescribed burns in three ~35-year-old mixed conifer plantations that had previously been masticated and thinned during February in order to demonstrate the effectiveness of winter burning, which is not common in the Sierra Nevada, California. Results On average, 59% of fine fuels were consumed and the fires reduced shrub cover by 94%. The average percent of crown volume that was damaged was 25%, with no mortality observed in overstory trees 1 year following the fires. A plot level analysis of the factors of fire effects did not find strong predictors of fuel consumption. Shrub cover was reduced dramatically, regardless of the specific structure that existed in plots. We found a positive relationship between crown damage and the two variables of Pinus ponderosa relative basal area and shrub cover. But these were not particularly strong predictors. An analysis of the weather conditions that have occurred at this site over the past 20 years indicated that there have consistently been opportunities to conduct winter burns. On average, 12 days per winter were feasible for burning using our criteria. Windows of time are short, typically 1 or 2 days, and may occur at any time during the winter season. Conclusions This study demonstrates that winter burning can be an important piece of broader strategies to reduce wildfire severity in the Sierra Nevada. Preparing forest structures so that they can be more feasible to burn and also preparing burn programs so that they can be nimble enough to burn opportunistically during short windows are key strategies. Both small landowners and large agencies may be able to explore winter burning opportunities to reduce wildfire severity.

Implementation constraints limit benefits of restoration treatments in mixed-conifer forests

2019 ◽  
Vol 28 (7) ◽  
pp. 495 ◽  
Author(s):  
Jamie M. Lydersen ◽  
Brandon M. Collins ◽  
Carolyn T. Hunsaker
Keyword(s):  
Sierra Nevada ◽  
Forest Structure ◽  
Forest Restoration ◽  
Tree Mortality ◽  
Canopy Cover ◽  
Basal Area ◽  
Severe Drought ◽  
Conifer Forest ◽  
Mixed Conifer ◽  
Trade Offs

Forest restoration treatments seek to increase resilience to wildfire and a changing climate while avoiding negative impacts to the ecosystem. The extent and intensity of treatments are often constrained by operational considerations and concerns over uncertainty in the trade-offs of addressing different management goals. The recent (2012–15) extreme drought in California, USA, resulted in widespread tree mortality, particularly in the southern Sierra Nevada, and provided an opportunity to assess the effects of restoration treatments on forest resilience to drought. We assessed changes in mixed-conifer forest structure following thinning and understorey burning at the Kings River Experimental Watersheds in the southern Sierra Nevada, and how treatments, topography and forest structure related to tree mortality in the recent drought. Treatments had negligible effect on basal area, tree density and canopy cover. Following the recent drought, average basal area mortality within the watersheds ranged from 5 to 26% across riparian areas and 12 to 44% across upland areas, with a range of 0 to 95% across all plots. Tree mortality was not significantly influenced by restoration treatments or topography. Our results suggest that the constraints common to many restoration treatments may limit their ability to mitigate the impacts of severe drought.

Tree mortality from fire and bark beetles following early and late season prescribed fires in a Sierra Nevada mixed-conifer forest

2006 ◽  
Vol 232 (1-3) ◽  
pp. 36-45 ◽  
Author(s):  
Dylan W. Schwilk ◽  
Eric E. Knapp ◽  
Scott M. Ferrenberg ◽  
Jon E. Keeley ◽  
Anthony C. Caprio
Keyword(s):  
Sierra Nevada ◽  
Bark Beetles ◽  
Tree Mortality ◽  
Prescribed Fires ◽  
Conifer Forest ◽  
Mixed Conifer ◽  
Late Season ◽  
Mixed Conifer Forest

Relating fuel loads to overstorey structure and composition in a fire-excluded Sierra Nevada mixed conifer forest

2015 ◽  
Vol 24 (4) ◽  
pp. 484 ◽  
Author(s):  
Jamie M. Lydersen ◽  
Brandon M. Collins ◽  
Eric E. Knapp ◽  
Gary B. Roller ◽  
Scott Stephens
Keyword(s):  
Sierra Nevada ◽  
Predictive Models ◽  
Vegetation Type ◽  
Fuel Load ◽  
Small Scale ◽  
Conifer Forest ◽  
Fire Behaviour ◽  
Mixed Conifer ◽  
Fuel Loads ◽  
Mixed Conifer Forest

Although knowledge of surface fuel loads is critical for evaluating potential fire behaviour and effects, their inherent variability makes these difficult to quantify. Several studies relate fuel loads to vegetation type, topography and spectral imaging, but little work has been done examining relationships between forest overstorey variables and surface fuel characteristics on a small scale (<0.05 ha). Within-stand differences in structure and composition would be expected to influence fuel bed characteristics, and thus affect fire behaviour and effects. We used intensive tree and fuel measurements in a fire-excluded Sierra Nevada mixed conifer forest to assess relationships and build predictive models for loads of duff, litter and four size classes of downed woody fuels to overstorey structure and composition. Overstorey variables explained a significant but somewhat small percentage of variation in fuel load, with marginal R2 values for predictive models ranging from 0.16 to 0.29. Canopy cover was a relatively important predictor for all fuel components, although relationships varied with tree species. White fir abundance had a positive relationship with total fine woody fuel load. Greater pine abundance was associated with lower load of fine woody fuels and greater load of litter. Duff load was positively associated with total basal area and negatively associated with oak abundance. Knowledge of relationships contributing to within-stand variation in fuel loads can increase our understanding of fuel accumulation and improve our ability to anticipate fine-scale variability in fire behaviour and effects in heterogeneous mixed species stands.

Managing burned landscapes: evaluating future management strategies for resilient forests under a warming climate

2014 ◽  
Vol 23 (7) ◽  
pp. 915 ◽  
Author(s):  
K. L. Shive ◽  
P. Z. Fulé ◽  
C. H. Sieg ◽  
B. A. Strom ◽  
M. E. Hunter
Keyword(s):  
Climate Change ◽  
Ponderosa Pine ◽  
Prescribed Burning ◽  
Fire Severity ◽  
Management Strategies ◽  
Basal Area ◽  
Forest Growth ◽  
Climate Change Effects ◽  
Ponderosa Pine Forests ◽  
And Shifts

Climate change effects on forested ecosystems worldwide include increases in drought-related mortality, changes to disturbance regimes and shifts in species distributions. Such climate-induced changes will alter the outcomes of current management strategies, complicating the selection of appropriate strategies to promote forest resilience. We modelled forest growth in ponderosa pine forests that burned in Arizona’s 2002 Rodeo–Chediski Fire using the Forest Vegetation Simulator Climate Extension, where initial stand structures were defined by pre-fire treatment and fire severity. Under extreme climate change, existing forests persisted for several decades, but shifted towards pinyon–juniper woodlands by 2104. Under milder scenarios, pine persisted with reduced growth. Prescribed burning at 10- and 20-year intervals resulted in basal areas within the historical range of variability (HRV) in low-severity sites that were initially dominated by smaller diameter trees; but in sites initially dominated by larger trees, the range was consistently exceeded. For high-severity sites, prescribed fire was too frequent to reach the HRV’s minimum basal area. Alternatively, for all stands under milder scenarios, uneven-aged management resulted in basal areas within the HRV because of its inherent flexibility to manipulate forest structures. These results emphasise the importance of flexible approaches to management in a changing climate.

Fuel treatments reduce the severity of wildfire effects in dry mixed conifer forest, Washington, USA

2010 ◽  
Vol 40 (8) ◽  
pp. 1615-1626 ◽  
Author(s):  
Susan J. Prichard ◽  
David L. Peterson ◽  
Kyle Jacobson
Keyword(s):  
Prescribed Burning ◽  
Fire Severity ◽  
Large Diameter ◽  
Severity Index ◽  
Prescribed Burn ◽  
Conifer Forest ◽  
Fuel Treatments ◽  
Quantitative Evidence ◽  
Control Units ◽  
And Control

To address hazardous fuel accumulations, many fuel treatments are being implemented in dry forests, but there have been few opportunities to evaluate treatment efficacy in wildfires. We documented the effectiveness of thinning and prescribed burning in the 2006 Tripod Complex fires. Recent fuel treatments burned in the wildfires and offered an opportunity to evaluate if two treatments (thin only and thin and prescribed burn) mitigated fire severity. Fire severity was markedly different between the two treatments. Over 57% of trees survived in thin and prescribed burn (thinRx) units versus 19% in thin only (thin) and 14% in control units. Considering only large-diameter trees (>20 cm diameter at breast height), 73% survived in thinRx units versus 36% and 29% in thin and control units, respectively. Logistic regression modeling demonstrates significant reductions in the log-odds probability of tree death under both treatments with a much greater reduction in thinRx units. Other severity measures, including percent crown scorch and burn severity index, are significantly lower in thinRx units than in thin and control units. This study provides strong quantitative evidence that thinning alone does not reduce wildfire severity but that thinning followed by prescribed burning is effective at mitigating wildfire severity in dry western forests.

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