Strong Legacy Effects of Prior Burn Severity on Forest Resilience to a High-Severity Fire

Research Highlights: The effects of fire on birds in the most northern parts of the boreal forest are understudied. We found distinct differences in bird communities with increasing fire severity in two vegetation types with naturally different burn severity. The highest severity burns tended to have communities dominated by generalist species, regardless of the original vegetation type. Background and Objectives: Wildfire is the primary natural disturbance in the boreal ecosystems of northwestern Canada. Increased wildfire frequency, extent, and severity are expected with climate change in this region. In particular, the proportion of burns that are high severity and the area of peatlands burned are increasing, and how this influences birds is poorly understood. Materials and Methods: We quantified the effects of burn severity (low, moderate, and high severity) in uplands and peatlands on occupancy, density, richness, community composition, and functional diversity using point counts (n = 1158) from the first two years post-fire for two large fires in the Northwest Territories, Canada. Results: Burn severity had a significant effect on the occupancy and density of 86% of our focal species (n = 20). Responses to burn severity depended on vegetation type for four of the 18 species using occupancy and seven of the 18 using density, but were typically in a similar direction. Species richness and functional diversity were lower in areas of high severity burns than unburned areas and low severity burns in peatlands. Richness was not related to severity in uplands, but functional diversity was. Peatlands had higher species richness than uplands in all burn severities, but as burn severity increased the upland and peatland communities became more similar. Conclusions: Our results suggest that high severity burns in both vegetation types support five generalist species and two fire specialists that may benefit from alterations in vegetation structure as a result of climate induced changes to fire regimes. However, eight species avoided burns, particularly birds preferring peatlands, and are likely to be more susceptible to fire-driven changes to their habitat caused by climate change. Understanding the long-term risks to these species from climate change requires additional efforts that link fire to bird populations.

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Efficacy of eastern Australian rainforests and topography as fire refugia under anthropogenic climate change

10.21203/rs.3.rs-295560/v1 ◽

2021 ◽

Author(s):

Myles Jay Bennell ◽

Philip Le C. Stewart ◽

Patrick T. Moss

Keyword(s):

Climate Change ◽

Ecosystem Services ◽

Fire Frequency ◽

Climate Feedback ◽

Burn Severity ◽

Future Research ◽

Feedback Systems ◽

High Severity ◽

Eastern Australia ◽

Vegetation Expansion

Abstract Background: The 2019-20 Australian bushfire season was the most environmentally detrimental bushfire season on record. The extreme heat and drought exposed normally fire-resistant communities to uncharacteristically dry fuel loads and abnormally high severity burning. In eastern Australia this included mesic rainforest environments (including the World Heritage listed Gondwana Rainforests of Australia), which are often highly sensitive to fire, contain high biodiversity values, are critical habitat for threatened species, embody distinct endemism, provide valuable ecosystem services and are critical for terrestrial carbon storage. East coast rainforests are also highly fragmented, with less than half of pre-European levels remaining. Increases in fire frequency and intensity associated with climate change may threaten these already fragmented rainforest environments. This study considers the efficacy of rainforest refugia under a heightened bushfire climate, via spatial analysis of burn extent, burn severity and topographic characteristics for rainforests during the 2019-20 bushfire season within the Eastern Australian Temperate and Subtropical Forests Conservation Management Zone.Results: Burn severity, vegetation and elevation datasets were merged and analysed across mid-eastern Australia. A significant portion of rainforest was fire affected across the study area (~17%), with ~5% burnt to a high or very high severity. Elevation, topographic position (i.e. valleys), slope and aspect all contributed to maintaining rainforest fire refugia. The study resulted in a mapping product that can be utilised by researchers and protected area managers to locate and assess burnt rainforest in mid-eastern Australia.Conclusions: This study enables the identification of rainforest fire refugia and threatened rainforest communities for future research and conservation efforts in eastern Australia. The results also demonstrate the potential of climate change to enact widespread rainforest declines, with potentially dire consequences for biodiversity and ecosystem services. This event and recurrent fire events may enact positive climate feedback systems by enabling pyrophytic vegetation expansion and converting rainforest carbon pools into a carbon source.

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Multidecadal trends in area burned with high severity in the Selway-Bitterroot Wilderness Area 1880–2012

International Journal of Wildland Fire ◽

10.1071/wf17023 ◽

2017 ◽

Vol 26 (11) ◽

pp. 930 ◽

Cited By ~ 12

Author(s):

Penelope Morgan ◽

Andrew T. Hudak ◽

Ashley Wells ◽

Sean A. Parks ◽

L. Scott Baggett ◽

...

Keyword(s):

Fire Management ◽

Early Period ◽

Burn Severity ◽

Area Burned ◽

High Severity ◽

Wilderness Area ◽

Severity Class ◽

Recent Trends ◽

Term Data

Multidecadal trends in areas burned with high severity shape ecological effects of fires, but most assessments are limited to ~30 years of satellite data. We analysed the proportion of area burned with high severity, the annual area burned with high severity, the probability areas burned with high severity and also the area reburned (all severities and high burn severity only) over 133 years across 346265ha within the Selway-Bitterroot Wilderness (SBW) Area in Idaho, United States. We used burn severity class inferred from digitised aerial photography (1880–2000) and satellite imagery (1973–2012). Over this long record, the proportion burned with high severity did not increase, despite extensive area burned in recent decades. Much greater area burned with high severity during the Early (1880–1934) and Late (1975–2012) periods than during the Middle period (1935–1974), paralleling trends in area burned. Little area reburned with high severity, and fires in the Early period limited the extent of fires burning decades later in the Late period. Our results suggest that long-term data across large areas provides useful context on recent trends, and that projections for the extent and severity of future fires must consider prior fires and fire management.

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Assessing Legacy Effects of Wildfires on the Crown Structure of Fire-Tolerant Eucalypt Trees Using Airborne Lidar Data

10.20944/preprints201910.0145.v1 ◽

2019 ◽

Author(s):

Yogendra K. Karna ◽

Trent D. Penman ◽

Cristina Aponte ◽

Lauren T. Bennett

Keyword(s):

Airborne Lidar ◽

Lidar Data ◽

Legacy Effects ◽

Individual Tree ◽

Tree Crowns ◽

High Severity ◽

Eucalypt Forest ◽

Crown Width ◽

In Fire ◽

Airborne Lidar Data

Fire-tolerant eucalypt forests of south eastern Australia are assumed to fully recover from even the most intense fires but surprisingly very few studies have quantitatively assessed that recovery. Accurate assessment of horizontal and vertical attributes of tree crowns after fire is essential to understand the fire’s legacy effects on tree growth and on forest structure. In this study, we quantitatively assessed individual tree crowns 8.5 years after a 2009 wildfire that burnt extensive areas of eucalypt forest in temperate Australia. We used airborne lidar data validated with field measurements to estimate multiple metrics that quantified the cover, density, and vertical distribution of individual-tree crowns in 51 plots of 0.05 ha in fire-tolerant eucalypt forest across four wildfire severity types (unburnt, low, moderate, high). Significant differences in the field-assessed mean height of fire scarring as a proportion of tree height, and in the proportions of trees with epicormic (stem) resprouts were consistent with the gradation in fire severity. Linear mixed-effects models indicated persistent effects of both moderate- and high-severity wildfire on tree crown architecture. Trees at high-severity sites had significantly less crown projection area and live crown width as a proportion of total crown width than those at unburnt and low-severity sites. Significant differences in lidar-based metrics (crown cover, evenness, leaf area density profiles) indicated that tree crowns at moderate- and high-severity sites were comparatively narrow and more evenly distributed down the tree stem. These conical-shaped crowns contrasted sharply with the rounded crowns of trees at unburnt and low-severity sites, and likely influenced both tree productivity and the accuracy of biomass allometric equations for nearly a decade after the fire. Our data provide a clear example of the utility of airborne lidar data for quantifying the impacts of disturbances at the scale of individual trees. Quantified effects of contrasting fire severities on the structure of resprouter tree crowns provide a strong basis for interpreting post-fire patterns in forest canopies and vegetation profiles in lidar and other remotely-sensed data at larger scales.

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Uso de herramientas de teledetección para el análisis de la severidad y estimación de gases de efecto invernadero (GEI) en incendios forestales de gran magnitud. Estudio de caso incendio La Rufina, VI Región del L. G. B. O’Higgins, Chile

Revista de Teledetección ◽

10.4995/raet.2017.8987 ◽

2017 ◽

pp. 59 ◽

Cited By ~ 1

Author(s):

P. Vidal ◽

A. De Santis ◽

W. Pérez ◽

P. Honeyman

Keyword(s):

Combustion Efficiency ◽

Burn Severity ◽

Tree Plantations ◽

Native Forest ◽

High Severity ◽

Landsat 7 ◽

Landsat 5 Tm ◽

Normalized Burn Ratio ◽

Different Levels ◽

Over Time

<p>Wildfires destroy thousands of hectares of vegetation every year in Chile, a phenomenon that has steadily increased over time, both in terms of the number of fires and the area affected. Since 1985 until 2016 have occurred 1,476 wildfires severe in intensity (> 200 ha), that burned a total of about 1,243,407 ha of vegetation, and an average of 40,000 ha affected per year. Depending on the type and intensity of the fire, there are different levels of severity with which the fire affects the vegetation, a variation that is crucial for the estimation GEI in the event. The purpose of this research was to analyze the burn severity of Rufina wildfires occurred in 1999, in the VI Region of L. G. B. O’Higgins in Chile, south of the capital Santiago, using Landsat 5 TM and Landsat 7 ETM+ imagery, including in the analysis the estimated greenhouse gases emitted in relation to with the vegetation and burn severity. Burn severity was estimated through the Normalized Burn Ratio (dNBR) and GEI with the equation proposed by IPCC in 2006, which was adjusted with the combustion efficiency coefficients proposed by De Santis et al. (2010). The results show that around 16,783 ha were affected by fires of different severity and the native forest and tree plantations were affected by high severity. The ton of GEI for each level of burn severity and type of vegetation was estimated, being carbon dioxide (CO<sub>2 </sub>) the main GEI emitted to the atmosphere in the fire. The highest emissions occurred in the areas of grasslands and scrublands, with high severity, with values ranging between 186 and 170 t/ha respectively</p>

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Burn Severity Effects on Sediment and Nutrient Exports from Southeastern Forests Using Simulated Rainfall

Forest Science ◽

10.1093/forsci/fxaa029 ◽

2020 ◽

Vol 66 (6) ◽

pp. 678-686 ◽

Cited By ~ 1

Author(s):

Kipling Klimas ◽

Patrick Hiesl ◽

Donald Hagan ◽

Dara Park

Keyword(s):

Sediment Yield ◽

Suspended Solids ◽

Total Suspended Solids ◽

Burn Severity ◽

Nutrient Concentrations ◽

Simulated Rainfall ◽

Forest Types ◽

Important Indicator ◽

Nutrient Response ◽

High Severity

Abstract Burn severity, commonly assessed as the amount of fuel consumed during fire, is an indicator of postfire sediment yield and erosion. This study examined the effect of burn severity on sediment and nutrient response in three different fire-adapted forest types of the Southeast. Soil and litter samples were experimentally burned to achieve increasing levels of fuel consumption. Simulated rainfall was applied to burned litter samples collected from pine, hardwood, and mixed hardwood-pine forests in the Clemson Experimental Forest. Runoff and leachate samples were collected and analyzed for sediment yield (kilograms per hectare) and total suspended solids (grams per liter); both runoff and leachate samples were analyzed for ammonium (NH4–), nitrate (NO3–), and orthophosphate (PO43–). Sediment yield and total suspended solids increased at only the highest burn severity treatment in all three forest types, with pine litter samples yielding significantly greater sediment in surface runoff than both mixed and hardwood samples. Burn treatment did not readily affect soluble nutrient concentrations in either runoff or leachate, but the data suggest that high-severity burning increases the availability of PO43– bound to sediment. This study suggests that high-severity burn patches function as sediment sources, but overall sediment and nutrient response to burning was minimal. Study Implications This study suggests that low-to-moderate burn severity, in terms of litter removal, is not an important indicator of sediment and nutrient exports from southeastern forests; precipitation in the immediate aftermath of fire (<48 hours) is not an effective transport mechanism for biologically available macronutrients; and that even at the highest burn severity treatment, sediment yield was relatively low.

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Corrigendum to: Altered mixed-severity fire regime has homogenised montane forests of Jasper National Park

International Journal of Wildland Fire ◽

10.1071/wf15048_co ◽

2016 ◽

Vol 25 (8) ◽

pp. 909

Author(s):

Raphaël D. Chavardès ◽

Lori D. Daniels

Keyword(s):

National Park ◽

Fire History ◽

Fire Regime ◽

Fire Suppression ◽

Montane Forests ◽

Jasper National Park ◽

High Severity ◽

Forest Resilience ◽

Canopy Trees ◽

Hybrid Spruce

Fire suppression has altered the historical mixed-severity fire regime and homogenised forest structures in Jasper National Park, Canada. We used dendrochronology to reconstruct fire history and assess forest dynamics at 29 sites in the montane forests. Based on fire scars and even-aged post-fire cohorts, we determined 18 sites had mixed-severity fire histories through time, and 11 sites had evidence of high-severity fires only – yielding a mixed-severity fire regime for the study area. Lodgepole pine, hybrid spruce and Douglas-fir established simultaneously after low- and high-severity fires. Regardless of fire history, forest canopies were mixed in composition and subcanopies were strongly dominated by shade-tolerant hybrid spruce. Despite their size, subcanopy trees were similar in age to the canopy trees. Current stand composition and age structures largely reflect the effects of high-severity fires that burned ~110 years ago at 18 of 29 sites. In the absence of fires after 1905, forests have matured simultaneously, homogenising the landscape and resulting in forest structures that are more conducive to high-severity fire than are fires of a range of severities. Proactive fire management is justified to restore fire as a vital ecological process and promote forest resilience by countering the effects of a century of fire suppression.

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Predictive modelling of burn probability and burn severity in a desert spring ecosystem

International Journal of Wildland Fire ◽

10.1071/wf11172 ◽

2012 ◽

Vol 21 (8) ◽

pp. 1014 ◽

Cited By ~ 4

Author(s):

Stephanie O. Sunderman ◽

Peter J. Weisberg

Keyword(s):

Fire Ecology ◽

Bayesian Model Averaging ◽

Riparian Forest ◽

Model Averaging ◽

Predictive Modelling ◽

Fire Regimes ◽

Burn Severity ◽

High Severity ◽

Burn Probability ◽

Desert Spring

Little is known about the fire ecology of desert springs, despite their importance for biodiversity and for provision of ecosystem services. Desert spring ecosystems are characterised by high and continuous fuel loads compared with surrounding uplands, suggesting that fire may play a significant ecological role. For the Ash Meadows spring complex in the south-western USA, we used ecological-niche factor analysis and a Bayesian model averaging regression technique to characterise the environmental conditions associated with spatially explicit burn probability and burn severity over a 24-year period. Burn probability and burn severity were both more strongly associated with fuel availability than with proximity to anthropogenic ignition sources; however, areas with more homogeneous vegetation cover were positively associated with high-severity burns but were negatively associated with burn probability. Burn probability was greater near areas of high anthropogenic influence, whereas areas further from anthropogenic alteration were more likely to experience high-severity fire. Riparian forest and emergent wetland vegetation were most likely to burn although they were among the rarest vegetation types. Human activities may strongly influence fire regimes in desert spring wetlands through groundwater pumping and introductions of exotic plants that alter fuelbed heterogeneity and shift the balance among woody and herbaceous vegetation.

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Influence of topography and forest structure on patterns of mixed severity fire in ponderosa pine forests of the South Dakota Black Hills, USA

International Journal of Wildland Fire ◽

10.1071/wf05096 ◽

2006 ◽

Vol 15 (4) ◽

pp. 557 ◽

Cited By ~ 66

Author(s):

Leigh B. Lentile ◽

Frederick W. Smith ◽

Wayne D. Shepperd

Keyword(s):

South Dakota ◽

Ponderosa Pine ◽

Stand Structure ◽

Stand Density ◽

Fire Effects ◽

Black Hills ◽

Burn Severity ◽

High Severity ◽

Density Index ◽

Stand Density Index

We examined the influence of topography and stand structure on fire effects within the perimeter of the ~34 000 ha Jasper fire of 2000 in ponderosa pine (Pinus ponderosa Laws.) forests of the South Dakota Black Hills, USA. We used a remotely sensed and field-verified map of post-fire burn severity (accuracy 69%, kappa statistic 0.54), the Digital Elevation Model, and vegetation databases maintained by the Black Hills National Forest to empirically test relationships at 500 randomly located points in each of three severity classes. Burn severity was defined as the relative degree of post-fire change based on fire effects on soil, forest floor, and vegetation. This fire burned rapidly, yet created a patchy mosaic of effects (25, 48, and 27% low, moderate, and high severity). Stands burned by low and moderate severity fire had fewer trees (stand density index <470 with fewer than 230 trees >13 cm diameter at breast height ha–1) and were found on less steep sites (slope < 18%). Denser stands (stand density index >470) with larger trees (average stand diameter >24 cm) or many small trees were more likely to burn with high severity effects. Our results suggest that managers should consider topography and stand structure together when making strategic decisions about which stands to thin or otherwise manage to reduce the severity with which forests will burn in wildfires.

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Extreme Winds Flip Influence of Fuels and Topography on Megafire Burn Severity in Mesic Conifer Forests Under Record Fuel Aridity

10.21203/rs.3.rs-654932/v1 ◽

2021 ◽

Author(s):

Cody Evers ◽

Sebastian Busby ◽

Max Nielsen-Pincus ◽

Andrés Holz

Keyword(s):

Land Use ◽

Tree Mortality ◽

Fire Regimes ◽

Relative Influence ◽

Burn Severity ◽

Fire Season ◽

Cascade Mountains ◽

Private Lands ◽

High Severity ◽

Extreme Winds

Abstract The coupling of unusually hot and dry weather have led to global increases in the occurrence of megafires. Despite the conventional wisdom that extreme heat and aridity overwhelm the controls on burn severity patterns (i.e., vegetation mortality), we hypothesize that wind is the main driver of megafire events in temperate mesic forests with climate-restricted fire regimes, yet that fuels and topography remain important influences on burn severity patterns. The infrequent occurrence of large high-severity wildfire in these forests means that contemporary empirical data (e.g., remote sensing) from past megafires are largely missing. During the extraordinary 2020 fire season, ca. 0.8 million ha burned in the North American Pacific Northwest (PNW) over two weeks under record-breaking fuel aridity and winds, representing the first modern example of megafires that characterize disturbance regimes west of the region’s Cascade Mountains. Considering increasing concern and uncertainty surrounding the drivers of megafire events in temperate mesic forests, our objective was to understand the relative influence of, and potential interactions between, weather, fuels, and topography on high-severity (> 75% tree mortality) fire probability among five synchronous megafires in the western Cascade Mountains. To assess the influence of several potential drivers of high-severity fire and whether these relationships varied with land use and ownership, we developed remotely sensed fire extent and burn severity maps for two periods of the explosive 2020 PNW fire season: (1) during extreme winds and (2) after the extreme winds subsided. The area burned during the windstorm accounted for 90% of the total fire sizes and saw a 2.5-times greater proportion of high-severity fire than during the period without winds. Our results suggest that wind is the major driver of megafires in forests with climate-limited fire regimes, yet that fuels and topography shape burn severity patterns even under extreme fuel aridity and winds. The relative influence of topography on burn severity outweighed fuels during the windstorm, while fuels outweighed the influence of topography after winds subsided. Early-seral forests primarily concentrated on private lands, burned more severely than their older and taller counterparts, regardless of topography, over the entire megafire event. Meanwhile, mature stands burned severely only under extreme winds and especially on steeper slopes. Although climate change and land-use legacies may prime mesic temperate forests to burn more frequently and at higher severities than historically observed, and especially among early-seral forests, our work suggests that future high-severity megafires are only likely to occur during coinciding periods of heat, fuel aridity, and extreme winds.

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