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Charcoal reflectance reveals early holocene boreal deciduous forests burned at high intensities.

Hudspith VA, Belcher CM, Kelly R, Hu FS - PLoS ONE (2015)

Bottom Line: For the first time, we have used reflectance measurements of macroscopic charcoal particles (>180μm) from an Alaskan lake-sediment record to estimate ancient charring temperatures (termed pyrolysis intensity).We demonstrate that pyrolysis intensity increased markedly from an interval of birch tundra 11 ky ago (mean 1.52%Ro; 485°C), to the expansion of trees on the landscape ~10.5 ky ago, remaining high to the present (mean 3.54%Ro; 640°C) irrespective of stand composition.Based on our analysis, we infer that predicted expansion of deciduous trees into the boreal forest in the future could lead to high intensity, but low severity fires, potentially moderating future climate-fire feedbacks.

View Article: PubMed Central - PubMed

Affiliation: Department of Plant Biology, University of Illinois at Urbana-Champaign, Urbana, Illinois, United States of America.

ABSTRACT
Wildfire size, frequency, and severity are increasing in the Alaskan boreal forest in response to climate warming. One of the potential impacts of this changing fire regime is the alteration of successional trajectories, from black spruce to mixed stands dominated by aspen, a vegetation composition not experienced since the early Holocene. Such changes in vegetation composition may consequently alter the intensity of fires, influencing fire feedbacks to the ecosystem. Paleorecords document past wildfire-vegetation dynamics and as such, are imperative for our understanding of how these ecosystems will respond to future climate warming. For the first time, we have used reflectance measurements of macroscopic charcoal particles (>180μm) from an Alaskan lake-sediment record to estimate ancient charring temperatures (termed pyrolysis intensity). We demonstrate that pyrolysis intensity increased markedly from an interval of birch tundra 11 ky ago (mean 1.52%Ro; 485°C), to the expansion of trees on the landscape ~10.5 ky ago, remaining high to the present (mean 3.54%Ro; 640°C) irrespective of stand composition. Despite differing flammabilities and adaptations to fire, the highest pyrolysis intensities derive from two intervals with distinct vegetation compositions. 1) the expansion of mixed aspen and spruce woodland at 10 cal. kyr BP, and 2) the establishment of black spruce, and the modern boreal forest at 4 cal. kyr BP. Based on our analysis, we infer that predicted expansion of deciduous trees into the boreal forest in the future could lead to high intensity, but low severity fires, potentially moderating future climate-fire feedbacks.

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Photomicrographs illustrating charcoals from ‘undegraded’ and ‘biodegraded’ categories, (A) undegraded gymnospermous woody fragment, (B) Plant tissue showing evidence of biodegradation prior to charring: the presence of cell infillings formed from biodegradation of the cell wall, distortion of cell walls, and cavity formation in secondary walls.Photographs were taken using reflected-light microscopy with immersion oil.
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pone.0120835.g003: Photomicrographs illustrating charcoals from ‘undegraded’ and ‘biodegraded’ categories, (A) undegraded gymnospermous woody fragment, (B) Plant tissue showing evidence of biodegradation prior to charring: the presence of cell infillings formed from biodegradation of the cell wall, distortion of cell walls, and cavity formation in secondary walls.Photographs were taken using reflected-light microscopy with immersion oil.

Mentions: In addition to measured reflectance, each Holocene charcoal particle was classified as ‘biodegraded’ or ‘undegraded’ based on whether the charcoal showed characters indicative of decay prior to charring [31] (Fig. 3B). Plant material in the litter layer commonly shows signs of biodegradation [32], therefore biodegraded charcoals (e.g. Fig. 3B) likely derive from surface fuels, hence represent litter fires; whereas undegraded charcoals (e.g. Fig. 3A) likely derive from crown fuels hence indicate crown fires. It is of note that undegraded charcoals primarily comprised unaltered woody plant material (illustrated in Fig. 3A) and spruce needles; however, roots and mosses can also be undegraded when charred, yet represent surface fuels. Neither were observed in this study.


Charcoal reflectance reveals early holocene boreal deciduous forests burned at high intensities.

Hudspith VA, Belcher CM, Kelly R, Hu FS - PLoS ONE (2015)

Photomicrographs illustrating charcoals from ‘undegraded’ and ‘biodegraded’ categories, (A) undegraded gymnospermous woody fragment, (B) Plant tissue showing evidence of biodegradation prior to charring: the presence of cell infillings formed from biodegradation of the cell wall, distortion of cell walls, and cavity formation in secondary walls.Photographs were taken using reflected-light microscopy with immersion oil.
© Copyright Policy
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4390342&req=5

pone.0120835.g003: Photomicrographs illustrating charcoals from ‘undegraded’ and ‘biodegraded’ categories, (A) undegraded gymnospermous woody fragment, (B) Plant tissue showing evidence of biodegradation prior to charring: the presence of cell infillings formed from biodegradation of the cell wall, distortion of cell walls, and cavity formation in secondary walls.Photographs were taken using reflected-light microscopy with immersion oil.
Mentions: In addition to measured reflectance, each Holocene charcoal particle was classified as ‘biodegraded’ or ‘undegraded’ based on whether the charcoal showed characters indicative of decay prior to charring [31] (Fig. 3B). Plant material in the litter layer commonly shows signs of biodegradation [32], therefore biodegraded charcoals (e.g. Fig. 3B) likely derive from surface fuels, hence represent litter fires; whereas undegraded charcoals (e.g. Fig. 3A) likely derive from crown fuels hence indicate crown fires. It is of note that undegraded charcoals primarily comprised unaltered woody plant material (illustrated in Fig. 3A) and spruce needles; however, roots and mosses can also be undegraded when charred, yet represent surface fuels. Neither were observed in this study.

Bottom Line: For the first time, we have used reflectance measurements of macroscopic charcoal particles (>180μm) from an Alaskan lake-sediment record to estimate ancient charring temperatures (termed pyrolysis intensity).We demonstrate that pyrolysis intensity increased markedly from an interval of birch tundra 11 ky ago (mean 1.52%Ro; 485°C), to the expansion of trees on the landscape ~10.5 ky ago, remaining high to the present (mean 3.54%Ro; 640°C) irrespective of stand composition.Based on our analysis, we infer that predicted expansion of deciduous trees into the boreal forest in the future could lead to high intensity, but low severity fires, potentially moderating future climate-fire feedbacks.

View Article: PubMed Central - PubMed

Affiliation: Department of Plant Biology, University of Illinois at Urbana-Champaign, Urbana, Illinois, United States of America.

ABSTRACT
Wildfire size, frequency, and severity are increasing in the Alaskan boreal forest in response to climate warming. One of the potential impacts of this changing fire regime is the alteration of successional trajectories, from black spruce to mixed stands dominated by aspen, a vegetation composition not experienced since the early Holocene. Such changes in vegetation composition may consequently alter the intensity of fires, influencing fire feedbacks to the ecosystem. Paleorecords document past wildfire-vegetation dynamics and as such, are imperative for our understanding of how these ecosystems will respond to future climate warming. For the first time, we have used reflectance measurements of macroscopic charcoal particles (>180μm) from an Alaskan lake-sediment record to estimate ancient charring temperatures (termed pyrolysis intensity). We demonstrate that pyrolysis intensity increased markedly from an interval of birch tundra 11 ky ago (mean 1.52%Ro; 485°C), to the expansion of trees on the landscape ~10.5 ky ago, remaining high to the present (mean 3.54%Ro; 640°C) irrespective of stand composition. Despite differing flammabilities and adaptations to fire, the highest pyrolysis intensities derive from two intervals with distinct vegetation compositions. 1) the expansion of mixed aspen and spruce woodland at 10 cal. kyr BP, and 2) the establishment of black spruce, and the modern boreal forest at 4 cal. kyr BP. Based on our analysis, we infer that predicted expansion of deciduous trees into the boreal forest in the future could lead to high intensity, but low severity fires, potentially moderating future climate-fire feedbacks.

Show MeSH
Related in: MedlinePlus