How Initial Forest Cover, Site Characteristics and Fire Severity Drive the Dynamics of the Southern Boreal Forest

Forest fires are a key driver of boreal landscape dynamics and are expected to increase with climate change in the coming decades. A profound understanding of the effects of fire upon boreal forest dynamics is thus critically needed for our ability to manage these ecosystems and conserve their services. In the present study, we investigate the long-term post-fire forest dynamics in the southern boreal forests of western Quebec using historical aerial photographs from the 1930s, alongside with modern aerial photographs from the 1990s. We quantify the changes in forest cover classes (i.e., conifers, mixed and broadleaved) for 16 study sites that were burned between 1940 and 1970. We then analyzed how interactions between pre-fire forest composition, site characteristics and a fire severity weather index (FSWI) affected the probability of changes in forest cover. In the 1930s, half of the cover of sampled sites were coniferous while the other half were broadleaved or mixed. Between the 1930s and the 1990s, 41% of the areas maintained their initial cover while 59% changed. The lowest probability of changes was found with initial coniferous cover and well drained till deposits. Moreover, an important proportion of 1930s broadleaved/mixed cover transitioned to conifers in the 1990s, which was mainly associated with high FSWI and well-drained deposits. Overall, our results highlight a relatively high resistance and resilience of southern boreal coniferous forests to fire, which suggest that future increase in fire frequency may not necessarily result in a drastic loss of conifers.

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High latitude cooling associated with landscape changes from North American boreal forest fires

Biogeosciences Discussions ◽

10.5194/bgd-9-12087-2012 ◽

2012 ◽

Vol 9 (9) ◽

pp. 12087-12136 ◽

Cited By ~ 3

Author(s):

B. M. Rogers ◽

J. T. Randerson ◽

G. B. Bonan

Keyword(s):

Boreal Forest ◽

High Latitude ◽

Forest Fires ◽

Boreal Forests ◽

Regional Climate ◽

Forest Composition ◽

Energy Budgets ◽

Surface Cooling ◽

Functional Variation ◽

Greenhouse Gasses

Abstract. Fires in the boreal forests of North America are generally stand-replacing, killing the majority of trees and initiating succession that may last over a century. Functional variation during succession can affect local surface energy budgets and, potentially, regional climate. Burn area across Alaska and Canada has increased in the last few decades and is projected to be substantially higher by the end of the 21st century because of a warmer climate with longer growing seasons. Here we simulated the changes in forest composition due to altered burn area using a stochastic model of fire occurrence, historical fire data from national inventories, and succession trajectories derived from remote sensing. When coupled to an Earth system model, younger vegetation from increased burning cooled the high-latitude atmosphere, primarily in the winter and spring, with noticeable feedbacks from the ocean and sea ice. Results from multiple scenarios suggest that a doubling of burn area would result in surface cooling of 0.23 ± 0.09 °C and 0.43 ± 0.12 °C for winter–spring and February–April time periods, respectively. This could provide a negative feedback to high-latitude terrestrial warming during winter on the order of 4–6% for a doubling, and 14–23% for a quadrupling, of burn area. Further work is needed to integrate all the climate drivers from boreal forest fires, including aerosols and greenhouse gasses.

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High-latitude cooling associated with landscape changes from North American boreal forest fires

Biogeosciences ◽

10.5194/bg-10-699-2013 ◽

2013 ◽

Vol 10 (2) ◽

pp. 699-718 ◽

Cited By ~ 54

Author(s):

B. M. Rogers ◽

J. T. Randerson ◽

G. B. Bonan

Keyword(s):

North America ◽

Boreal Forest ◽

High Latitude ◽

Forest Fires ◽

Boreal Forests ◽

Regional Climate ◽

Forest Composition ◽

Energy Budgets ◽

Functional Variation ◽

Greenhouse Gasses

Abstract. Fires in the boreal forests of North America are generally stand-replacing, killing the majority of trees and initiating succession that may last over a century. Functional variation during succession can affect local surface energy budgets and, potentially, regional climate. Burn area across Alaska and Canada has increased in the last few decades and is projected to be substantially higher by the end of the 21st century because of a warmer climate with longer growing seasons. Here we simulated changes in forest composition due to altered burn area using a stochastic model of fire occurrence, historical fire data from national inventories, and succession trajectories derived from remote sensing. When coupled to an Earth system model, younger vegetation from increased burning cooled the high-latitude atmosphere, primarily in the winter and spring, with noticeable feedbacks from the ocean and sea ice. Results from multiple scenarios suggest that a doubling of burn area would cool the surface by 0.23 &pm; 0.09 °C across boreal North America during winter and spring months (December through May). This could provide a negative feedback to winter warming on the order of 3–5% for a doubling, and 14–23% for a quadrupling, of burn area. Maximum cooling occurs in the areas of greatest burning, and between February and April when albedo changes are largest and solar insolation is moderate. Further work is needed to integrate all the climate drivers from boreal forest fires, including aerosols and greenhouse gasses.

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Spatial variability of stand-scale residuals in Ontario’s boreal forest fires

Canadian Journal of Forest Research ◽

10.1139/x09-024 ◽

2009 ◽

Vol 39 (5) ◽

pp. 945-961 ◽

Cited By ~ 18

Author(s):

Ajith H. Perera ◽

Benjamin D. Dalziel ◽

Lisa J. Buse ◽

Robert G. Routledge

Keyword(s):

Spatial Variability ◽

Boreal Forest ◽

Forest Fires ◽

Boreal Forests ◽

Forest Cover ◽

Fire Intensity ◽

Site Conditions ◽

Linear Mixed Effects ◽

Ecological Applications ◽

Live Tree

Knowledge of postfire residuals in boreal forest landscapes is increasingly important for ecological applications and forest management. While many studies provide useful insight, knowledge of stand-scale postfire residual occurrence and variability remains fragmented and untested as formal hypotheses. We examined the spatial variability of stand-scale postfire residuals in boreal forests and tested hypotheses of their spatial associations. Based on the literature, we hypothesized that preburn forest cover characteristics, site conditions, proximity to water and fire edge, and local fire intensity influence the spatial variability of postfire residuals. To test these hypotheses, we studied live-tree and snag residuals in 11 boreal Ontario forest fires, using 660 sample points based on high resolution photography (1:408) captured immediately after the fires. The abundance of residuals varied considerably within and among these fires, precluding attempts to generalize estimates. Based on a linear mixed-effects model, our data did not support the hypotheses that preburn forest cover characteristics, site conditions, and proximity to water significantly affect the spatial variability of stand-scale residuals. The results do indicate, however, that stand-scale residual variability is associated with local fire intensity (strongly) and distance to fire edge (weakly).

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Resilience of the boreal forest in response to Holocene fire-frequency changes assessed by pollen diversity and population dynamics

International Journal of Wildland Fire ◽

10.1071/wf09097 ◽

2010 ◽

Vol 19 (8) ◽

pp. 1026 ◽

Cited By ~ 36

Author(s):

Christopher Carcaillet ◽

Pierre J. H. Richard ◽

Yves Bergeron ◽

Bianca Fréchette ◽

Adam A. Ali

Keyword(s):

Boreal Forest ◽

Boreal Forests ◽

Frequency Control ◽

Regional Scale ◽

Fire Regimes ◽

Fire Frequency ◽

Frequency Changes ◽

Fire Intervals ◽

In Fire

The hypothesis that changes in fire frequency control the long-term dynamics of boreal forests is tested on the basis of paleodata. Sites with different wildfire histories at the regional scale should exhibit different vegetation trajectories. Mean fire intervals and vegetation reconstructions are based respectively on sedimentary charcoal and pollen from two small lakes, one in the Mixedwood boreal forests and the second in the Coniferous boreal forests. The pollen-inferred vegetation exhibits different trajectories of boreal forest dynamics after afforestation, whereas mean fire intervals have no significant or a delayed impact on the pollen data, either in terms of diversity or trajectories. These boreal forests appear resilient to changes in fire regimes, although subtle modifications can be highlighted. Vegetation compositions have converged during the last 1200 years with the decrease in mean fire intervals, owing to an increasing abundance of boreal species at the southern site (Mixedwood), whereas changes are less pronounced at the northern site (Coniferous). Although wildfire is a natural property of boreal ecosystems, this study does not support the hypothesis that changes in mean fire intervals are the key process controlling long-term vegetation transformation. Fluctuations in mean fire intervals alone do not explain the historical and current distribution of vegetation, but they may have accelerated the climatic process of borealisation, likely resulting from orbital forcing.

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Understory alder in three boreal forests of Alaska: local distribution and effects on soil fertility

Canadian Journal of Forest Research ◽

10.1139/x95-107 ◽

1995 ◽

Vol 25 (6) ◽

pp. 987-996 ◽

Cited By ~ 19

Author(s):

Tricia L. Wurtz

Keyword(s):

Soil Fertility ◽

Boreal Forest ◽

Total Nitrogen ◽

Boreal Forests ◽

Soil Chemistry ◽

Canopy Openness ◽

Biomass Models ◽

Site Characteristics ◽

Undisturbed Forest ◽

Ramet Density

The distribution and effects on soil chemistry of shrub alders (Alnus spp.) occurring in the understory of the boreal forest of Alaska were examined. Understory alder ramet distribution was mapped on three sites; ramet density ranged from 150 to 5280 ramets/ha. Allometric biomass models were developed for alder ramets; maps of the spatial distribution of ramets and of estimated aboveground alder biomass are presented. Biomass of alders in the understory ranged from 20 to 690 g•m−2. The total nitrogen of soils collected beneath alder and from areas without alder differed among the three sites and between two sampling episodes. In undisturbed forest, alder soils tended to have more nitrogen than nonalder soils. On the two sites where background soil fertility was low, a greenhouse bioassay matched these results: alder soils had greater nutrient-supplying capacity than nonalder soils. In soil collected after the sites were harvested, however, results varied. Areas that had supported dense alder before harvesting had more soil nitrogen than areas with no alder at only one site, and at another site, alder soils had significantly less total nitrogen. This study suggests that the effect of understory alders on the boreal forest soil mosaic is a function of site characteristics such as canopy openness and soil background fertility.

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Relative importance of different secondary successional pathways in an Alaskan boreal forest

Canadian Journal of Forest Research ◽

10.1139/x08-039 ◽

2008 ◽

Vol 38 (7) ◽

pp. 1911-1923 ◽

Cited By ~ 39

Author(s):

Thomas A. Kurkowski ◽

Daniel H. Mann ◽

T. Scott Rupp ◽

David L. Verbyla

Keyword(s):

Boreal Forest ◽

Tree Species ◽

Black Spruce ◽

Fire Frequency ◽

Forest Composition ◽

Stand Age ◽

Solar Insolation ◽

Species Dominance ◽

Complex Landscape ◽

Successional Pathways

Postfire succession in the Alaskan boreal forest follows several different pathways, the most common being self-replacement and species-dominance relay. In self-replacement, canopy-dominant tree species replace themselves as the postfire dominants. It implies a relatively unchanging forest composition through time maintained by trees segregated within their respective, ecophysiological niches on an environmentally complex landscape. In contrast, species-dominance relay involves the simultaneous, postfire establishment of multiple tree species, followed by later shifts in canopy dominance. It implies that stand compositions vary with time since last fire. The relative frequencies of these and other successional pathways are poorly understood, despite their importance in determining the species mosaic of the present forest and their varying, potential responses to climate changes. Here we assess the relative frequencies of different successional pathways by modeling the relationship between stand type, solar insolation, and altitude; by describing how stand age relates to species composition; and by inferring successional trajectories from stand understories. Results suggest that >70% of the study forest is the product of self-replacement, and tree distributions are controlled mainly by the spatial distribution of solar insolation and altitude, not by time since last fire. As climate warms over the coming decades, deciduous trees will invade cold sites formerly dominated by black spruce, and increased fire frequency will make species-dominance relay even rarer.

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Strong anthropogenic signals in historic forest fire regime: a detailed spatiotemporal case study from south-central Norway

Canadian Journal of Forest Research ◽

10.1139/cjfr-2012-0462 ◽

2013 ◽

Vol 43 (9) ◽

pp. 836-845 ◽

Cited By ~ 13

Author(s):

Ken Olaf Storaunet ◽

Jørund Rolstad ◽

Målfrid Toeneiet ◽

Ylva-li Blanck

Keyword(s):

Forest Fires ◽

Boreal Forests ◽

Fire Regime ◽

Fire Severity ◽

Fire Regimes ◽

Fire Scars ◽

Time Intervals ◽

Slash And Burn ◽

South Central

To better understand the historic range of variability in the fire regime of Fennoscandian boreal forests we cross-dated 736 fire scars of remnant Scots pine (Pinus sylvestris L.) wood samples in a 3.6 km2 section of the Trillemarka-Rollagsfjell Reserve of south-central Norway. Using a kernel range application in GIS we spatially delineated 57 individual forest fires between 1350 and the present. We found a strong anthropogenic signal in the fire regime from 1600 and onwards: (i) infrequent variably sized fires prior to 1600 shifted to frequent fires gradually decreasing in size during the 1600s and 1700s, with only a few small fires after 1800; (ii) time intervals between fires and the hazard of burning showed substantial differences pre- and post-1600; (iii) fire seasonality changed from late- to early-season fires from the 1626 fire and onwards; and (iv) fire severity decreased gradually over time. Written sources corroborated our results, narrating a history where anthropogenic forest fires and slash-and-burn cultivation expanded with the increasing population from the late 1500s. Concurrently, timber resources increased in value, gradually forcing slash-and-burn cultivators to abandon fires on forest land. Our results strengthen and expand previous Fennoscandian findings on the anthropogenic influence of historic fire regimes.

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Partial windthrow as a driving process of forest dynamics in old-growth boreal forests

Canadian Journal of Forest Research ◽

10.1139/cjfr-2013-0224 ◽

2014 ◽

Vol 44 (10) ◽

pp. 1165-1176 ◽

Cited By ~ 22

Author(s):

François Girard ◽

Louis De Grandpré ◽

Jean-Claude Ruel

Keyword(s):

Boreal Forest ◽

Forest Dynamics ◽

Boreal Forests ◽

Tree Mortality ◽

Stand Structure ◽

Temporal Dynamics ◽

Spruce Budworm ◽

Climatic Conditions ◽

Balsam Fir ◽

Vegetation Development

As climate changes, boreal forest ecosystems may become subject to disturbances that were previously uncommon in some regions. In recent decades, large tracts of northeastern boreal forest of Canada have been affected by different types of climatic events causing a lot of partial and some total stand mortality. Since these disturbances may become more important drivers of forest dynamics, there is a need to document their impact on forest structure. The objectives of this study were to describe temporal dynamics of partial windthrows and determine the effect of partial windthrow on stand composition and understory vegetation. The study was conducted in the North-Shore region of Quebec (Canada). Eighteen plots in closed forests were paired with 18 adjacent windthrow areas, in which trees experienced similar edaphic and climatic conditions. Dendroecological analyses, combined with vegetation sampling, were conducted on each site to determine stand structure and vegetation development through time. Significant increases in balsam fir and shade-tolerant species were observed in windthrow gaps. Tree mortality in windthrown stands was a slow process until the mid-1990s, a period during which spruce budworm defoliation may have played a role in weakening trees and making them more vulnerable to partial windthrow. Greater mortality observed following the mid-1990s was most certainly related to a regional storm. The initial composition of stands plays an important role in driving postwindthrow succession, as balsam fir is more susceptible to treefall. As opposed to stand-replacing windthrow and spruce budworm outbreaks that generate various postdisturbance responses, partial windthrow appears to only create opportunities for pre-established balsam fir to undergo release in gaps.

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Drought Modulated Boreal Forest Fire Occurrence and Linkage with La Nina Events in Altai Mountains, Northwest China

10.20944/preprints202008.0001.v1 ◽

2020 ◽

Author(s):

Chunming Shi ◽

Ying Liang ◽

Cong Gao ◽

Fengjun Zhao ◽

Qiuhua Wang ◽

...

Keyword(s):

Drought Stress ◽

Boreal Forest ◽

Forest Fire ◽

El Niño ◽

Boreal Forests ◽

El Nino ◽

Fire Frequency ◽

Burned Area ◽

Fire Occurrence ◽

La Nina

Warming-induced drought stress and El Nino associated summer precipitation failure are responsible for increased forest fire intensities of tropical and temperate forests in Asia and Australia. However, both effects are unclear for boreal forests, the largest biome and carbon stock over land. Here we combined fire frequency, burned area and climate data in the Altai boreal forests, the southmost extension of Siberia boreal forest into China, and explored their link with ENSO (El Nino and South Oscillation). Surprisingly, both summer drought severity and fire occurrence have shown significant (P&lt;0.05) teleconnections with La Nina events of the previous year, and therefore provide an important reference for forest fire prediction and prevention in Altai. Despite a significant warming trend, the increased moisture over Altai has largely offset the effect of warming-induced drought stress, and lead to an insignificant fire frequency trend in the last decades, and largely reduced burned area since the 1980s. The reduced burned area could also benefit from the fire suppression efforts and greatly increased investment in fire prevention since 1987.

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