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Frequent fires in ancient shrub tundra: implications of paleorecords for arctic environmental change.

Higuera PE, Brubaker LB, Anderson PM, Brown TA, Kennedy AT, Hu FS - PLoS ONE (2008)

Bottom Line: We present paleoecological data that indicate frequent tundra fires in northcentral Alaska between 14,000 and 10,000 years ago.Charcoal and pollen from lake sediments reveal that ancient birch-dominated shrub tundra burned as often as modern boreal forests in the region, every 144 years on average (+/- 90 s.d.; n = 44).These records suggest that greater fire activity will likely accompany temperature-related increases in shrub-dominated tundra predicted for the 21(st) century and beyond.

View Article: PubMed Central - PubMed

Affiliation: College of Forest Resources, University of Washington, Seattle, Washington, USA. philip.higuera@montana.edu

ABSTRACT
Understanding feedbacks between terrestrial and atmospheric systems is vital for predicting the consequences of global change, particularly in the rapidly changing Arctic. Fire is a key process in this context, but the consequences of altered fire regimes in tundra ecosystems are rarely considered, largely because tundra fires occur infrequently on the modern landscape. We present paleoecological data that indicate frequent tundra fires in northcentral Alaska between 14,000 and 10,000 years ago. Charcoal and pollen from lake sediments reveal that ancient birch-dominated shrub tundra burned as often as modern boreal forests in the region, every 144 years on average (+/- 90 s.d.; n = 44). Although paleoclimate interpretations and data from modern tundra fires suggest that increased burning was aided by low effective moisture, vegetation cover clearly played a critical role in facilitating the paleofires by creating an abundance of fine fuels. These records suggest that greater fire activity will likely accompany temperature-related increases in shrub-dominated tundra predicted for the 21(st) century and beyond. Increased tundra burning will have broad impacts on physical and biological systems as well as on land-atmosphere interactions in the Arctic, including the potential to release stored organic carbon to the atmosphere.

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Related in: MedlinePlus

Fire and vegetation reconstructions from northcentral Alaska.Chronology, pollen stratigraphy, inferred vegetation, and high-frequency variations in charcoal accumulation rates (CHARs) from (A) Xindi Lake and (B) Ruppert Lake. Pollen percentage curves are smoothed to 500 years and color coded. CHAR records represent residuals after removing 500-year trends, and red lines around CHAR = 0 are thresholds identifying noise-related variations. Red plus marks identify CHAR peaks exceeding the positive threshold (and a minimum-count screening; see Materials and Methods) and are interpreted as local fire events. At both sites CHARs and CHAR peaks increase distinctly with the rise in Betula pollen percentages, marking the transition from the Herb Tundra Zone to the Shrub Tundra Zone.
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pone-0001744-g002: Fire and vegetation reconstructions from northcentral Alaska.Chronology, pollen stratigraphy, inferred vegetation, and high-frequency variations in charcoal accumulation rates (CHARs) from (A) Xindi Lake and (B) Ruppert Lake. Pollen percentage curves are smoothed to 500 years and color coded. CHAR records represent residuals after removing 500-year trends, and red lines around CHAR = 0 are thresholds identifying noise-related variations. Red plus marks identify CHAR peaks exceeding the positive threshold (and a minimum-count screening; see Materials and Methods) and are interpreted as local fire events. At both sites CHARs and CHAR peaks increase distinctly with the rise in Betula pollen percentages, marking the transition from the Herb Tundra Zone to the Shrub Tundra Zone.

Mentions: Trends in charcoal accumulation rates (pieces cm−2 yr−1, CHARs) correspond markedly with shifts in pollen assemblages at Xindi and Ruppert lakes (Fig. 2). Both records start in herb-dominated tundra (Herb Tundra Zone), indicated by high pollen percentages of Cyperaceae (sedge), Poaceae (grass), and minor herb taxa (e.g. Artemisia [wormwood], data not shown). Raw CHARs are low (medians = 0.01 and 0.00 pieces cm−2 yr−1) with few identified peaks in the detrended series (Fig. 2), suggesting little or no burning in the late-glacial herb tundra near these sites. Increases in CHARs (medians = 0.05 and 0.02 pieces cm−2 yr−1) and the frequency of peaks in the detrended series coincide with a prominent rise in Betula (birch) pollen percentages (from <5 to 50–75%; 14.3 and 13.3 ka BP at Xindi and Ruppert lakes, respectively), which marks the expansion of Betula shrubs in the study area (Fig. 2). These pollen assemblages (Shrub Tundra Zone) have higher Betula percentages than pollen assemblages from modern tundra in North America [13] (e.g. 70% vs. 40%) and are thought to represent extensive thickets of tall (>1 m) Betula glandulosa [resin birch, inferred from measurements of pollen morphology, 14]. The inferred vegetation of the Shrub Tundra Zone contrasts with the majority of modern circumpolar Arctic tundra, where only 12% of the area contains shrubs taller than 0.4 m [i.e. Low-shrub tundra; 15]. However, the vegetation structure of the Shrub Tundra Zone may be analogous to future Arctic tundra, which is predicted to have a major component of >0.5-m tall Betula, Salix (willow), and Alnus (alder) shrubs [10], [16]. Deciduous woodlands (Deciduous Woodland Zone), identified by samples with >10–20% Populus (poplar) pollen, characterized the vegetation from 10.5-9.0 ka BP (Fig. 2). As in the Herb Tundra Zone, the low raw CHARs (medians = 0.02 and 0.01 pieces cm−2 yr−1) and few peaks in the detrended series suggest less frequent fires as compared to the Shrub Tundra Zone.


Frequent fires in ancient shrub tundra: implications of paleorecords for arctic environmental change.

Higuera PE, Brubaker LB, Anderson PM, Brown TA, Kennedy AT, Hu FS - PLoS ONE (2008)

Fire and vegetation reconstructions from northcentral Alaska.Chronology, pollen stratigraphy, inferred vegetation, and high-frequency variations in charcoal accumulation rates (CHARs) from (A) Xindi Lake and (B) Ruppert Lake. Pollen percentage curves are smoothed to 500 years and color coded. CHAR records represent residuals after removing 500-year trends, and red lines around CHAR = 0 are thresholds identifying noise-related variations. Red plus marks identify CHAR peaks exceeding the positive threshold (and a minimum-count screening; see Materials and Methods) and are interpreted as local fire events. At both sites CHARs and CHAR peaks increase distinctly with the rise in Betula pollen percentages, marking the transition from the Herb Tundra Zone to the Shrub Tundra Zone.
© Copyright Policy
Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC2254503&req=5

pone-0001744-g002: Fire and vegetation reconstructions from northcentral Alaska.Chronology, pollen stratigraphy, inferred vegetation, and high-frequency variations in charcoal accumulation rates (CHARs) from (A) Xindi Lake and (B) Ruppert Lake. Pollen percentage curves are smoothed to 500 years and color coded. CHAR records represent residuals after removing 500-year trends, and red lines around CHAR = 0 are thresholds identifying noise-related variations. Red plus marks identify CHAR peaks exceeding the positive threshold (and a minimum-count screening; see Materials and Methods) and are interpreted as local fire events. At both sites CHARs and CHAR peaks increase distinctly with the rise in Betula pollen percentages, marking the transition from the Herb Tundra Zone to the Shrub Tundra Zone.
Mentions: Trends in charcoal accumulation rates (pieces cm−2 yr−1, CHARs) correspond markedly with shifts in pollen assemblages at Xindi and Ruppert lakes (Fig. 2). Both records start in herb-dominated tundra (Herb Tundra Zone), indicated by high pollen percentages of Cyperaceae (sedge), Poaceae (grass), and minor herb taxa (e.g. Artemisia [wormwood], data not shown). Raw CHARs are low (medians = 0.01 and 0.00 pieces cm−2 yr−1) with few identified peaks in the detrended series (Fig. 2), suggesting little or no burning in the late-glacial herb tundra near these sites. Increases in CHARs (medians = 0.05 and 0.02 pieces cm−2 yr−1) and the frequency of peaks in the detrended series coincide with a prominent rise in Betula (birch) pollen percentages (from <5 to 50–75%; 14.3 and 13.3 ka BP at Xindi and Ruppert lakes, respectively), which marks the expansion of Betula shrubs in the study area (Fig. 2). These pollen assemblages (Shrub Tundra Zone) have higher Betula percentages than pollen assemblages from modern tundra in North America [13] (e.g. 70% vs. 40%) and are thought to represent extensive thickets of tall (>1 m) Betula glandulosa [resin birch, inferred from measurements of pollen morphology, 14]. The inferred vegetation of the Shrub Tundra Zone contrasts with the majority of modern circumpolar Arctic tundra, where only 12% of the area contains shrubs taller than 0.4 m [i.e. Low-shrub tundra; 15]. However, the vegetation structure of the Shrub Tundra Zone may be analogous to future Arctic tundra, which is predicted to have a major component of >0.5-m tall Betula, Salix (willow), and Alnus (alder) shrubs [10], [16]. Deciduous woodlands (Deciduous Woodland Zone), identified by samples with >10–20% Populus (poplar) pollen, characterized the vegetation from 10.5-9.0 ka BP (Fig. 2). As in the Herb Tundra Zone, the low raw CHARs (medians = 0.02 and 0.01 pieces cm−2 yr−1) and few peaks in the detrended series suggest less frequent fires as compared to the Shrub Tundra Zone.

Bottom Line: We present paleoecological data that indicate frequent tundra fires in northcentral Alaska between 14,000 and 10,000 years ago.Charcoal and pollen from lake sediments reveal that ancient birch-dominated shrub tundra burned as often as modern boreal forests in the region, every 144 years on average (+/- 90 s.d.; n = 44).These records suggest that greater fire activity will likely accompany temperature-related increases in shrub-dominated tundra predicted for the 21(st) century and beyond.

View Article: PubMed Central - PubMed

Affiliation: College of Forest Resources, University of Washington, Seattle, Washington, USA. philip.higuera@montana.edu

ABSTRACT
Understanding feedbacks between terrestrial and atmospheric systems is vital for predicting the consequences of global change, particularly in the rapidly changing Arctic. Fire is a key process in this context, but the consequences of altered fire regimes in tundra ecosystems are rarely considered, largely because tundra fires occur infrequently on the modern landscape. We present paleoecological data that indicate frequent tundra fires in northcentral Alaska between 14,000 and 10,000 years ago. Charcoal and pollen from lake sediments reveal that ancient birch-dominated shrub tundra burned as often as modern boreal forests in the region, every 144 years on average (+/- 90 s.d.; n = 44). Although paleoclimate interpretations and data from modern tundra fires suggest that increased burning was aided by low effective moisture, vegetation cover clearly played a critical role in facilitating the paleofires by creating an abundance of fine fuels. These records suggest that greater fire activity will likely accompany temperature-related increases in shrub-dominated tundra predicted for the 21(st) century and beyond. Increased tundra burning will have broad impacts on physical and biological systems as well as on land-atmosphere interactions in the Arctic, including the potential to release stored organic carbon to the atmosphere.

Show MeSH
Related in: MedlinePlus