DOI: 10.25921/0gcc-ax86
title: NOAA/WDS Paleoclimatology - Higuera fire data from Wild Tussock Lake, South-Central Brooks Range, Alaska - IMPD USWK-001

description: We examined direct and indirect impacts of millennial-scale climate change on fire regimes in the south-central Brooks Range, Alaska, USA, using four lake sediment records and existing paleoclimate interpretations. New techniques were introduced to identify charcoal peaks semi-objectively and to detect statistical differences between fire regimes. Peaks in charcoal accumulation rates provided estimates of fire return intervals (FRIs), which were compared among vegetation zones identified by fossil pollen and stornata. Climatic warming between ca. 15 000-9000 yr BP (calendar years before Common Era [CE] 1950) coincided with shifts in vegetation from herb tundra to shrub tundra to deciduous woodlands, all novel species assemblages relative to modern vegetation. Two sites cover this period and show decreased FRIs with the transition from herb to Betula-dominated shrub tundra ca. 13 300- 14300 yr BP (FRImean = 144 yr; 95% CI = 120-169 yr), when climate warmed but remained cooler than present. Although warming would have favored shorter FRIs in the shrub tundra, the shift to more continuous, flammable fuels relative to herb tundra was probably a more important cause of increased burning. Similarly, a vegetation shift to Populus-dominated deciduous woodlands overrode the influence of warmer- and drier-than-present summers, resulting in lower fire activity from ca. 10 300-8250 yr BP (FRImean = 251 yr; 95% CI = 156- 347 yr). Three sites record the mid-to-late Holocene, when climatic cooling and moistening allowed Picea glauca forest-tundra and P. mariana boreal forests to establish ca. 8000 and 5500 yr BP, respectively. FRIs in forest-tundra were either similar to or shorter than those in the deciduous woodlands (FRImean range = 131-238 yr). The addition of P. mariana ca. 5500 yr BP increased landscape flammability, overrode the effects of climatic cooling and moistening and resulted in lower FRIs (FRImean= 145 yr; 95% CI = 130-163). Overall, shifts in fire regimes were strongly linked to changes in vegetation, which were responding to millennial-scale climate change. We conclude that shifts in vegetation can amplify or override the direct influence of climate change on fire regimes, when vegetation shifts significantly modify landscape flammability. Our findings emphasize the importance of biophysical feedbacks between climate, fire, and vegetation in determining the response of ecosystems to past, and by inference, future climate change.
description: Wild Tussock Lake data file contents: 
(1.) uswk-001.txt – contains: (a.) metadata, (b.) charcoal data in the "Data" section (which is the same as data the charcoal data in uswk-001-chardata.csv [CharAnalysis input file, See https://sites.google.com/site/charanalysis/ for more details]), and (c.) a "Chronology" section which includes depth and age data from the published age-depth model, and radiocarbon dates (radiocarbon dates are also locted in “Higuera_et_al_2009_Table_B1”in the folder titled “C14_dates” as published here: http://www.esapubs.org/archive/mono/M079/007/). Online Resource: http://www.ncei.noaa.gov/pub/data/paleo/firehistory/charcoal/northamerica/uswk-001.txt, 

(2.) uswk-001-age-depth-fig.pdf – Figure of the age-depth model, 1/4 of Fig. 2 in Higuera et al. (2009). Online_Resource: http://www.ncei.noaa.gov/pub/data/paleo/firehistory/charcoal/northamerica/supplemental/uswk-001-age-depth-fig.pdf, 

(3.) uswk-001-chardata.csv – Charcoal data in a CharAnalysis input file. Units are in the column headers: See https://sites.google.com/site/charanalysis/ for more details. Note: the data in this file is the same as the data in the "Data" section of: http://www.ncei.noaa.gov/pub/data/paleo/firehistory/charcoal/northamerica/uswk-001.txt. Online_Resource: http://www.ncei.noaa.gov/pub/data/paleo/firehistory/charcoal/northamerica/supplemental/uswk-001-chardata.csv, 

(4.) uswk-001-charparams.csv – Parameter file CharAnalysis, with parameters as used in the original publication. See https://sites.google.com/site/charanalysis/ for more details. Online_Resource: http://www.ncei.noaa.gov/pub/data/paleo/firehistory/charcoal/northamerica/supplemental/uswk-001-charparams.csv, 

(5.) uswk-001-charresults.csv – CharAnalysis results file. Units are in the column headers: See https://sites.google.com/site/charanalysis/ for more details. Online_Resource: http://www.ncei.noaa.gov/pub/data/paleo/firehistory/charcoal/northamerica/supplemental/uswk-001-charresults.csv, 

(6.) uswk-001-pollen.xls – Pollen counts for each sample. The tab “pollen_counts” and “pollen_cm” contains raw the same data as in the tab “data” but in a raw format used for plotting. Ages associated with each pollen sample have to be obtained from the "Chronology, Depth (cm) and age (cal yr BP) from the published age-depth model" section of file “uswk-001.txt”. Online_Resource: http://www.ncei.noaa.gov/pub/data/paleo/firehistory/charcoal/northamerica/supplemental/uswk-001-pollen.xls.; 

Keywords, Alaska (USA), arctic, boreal forest, charcoal analysis, climate change, deciduous woodland, fire history, landscape flammability, pollen analysis, shrub tundra, tundra; 

Site size(ha), 2; 

Sigle; 

Entity name, CO (Internal lab code); 

Investigators; 

Contact person, Philip Higuera, phiguera@uidaho.edu, pehiguera@gmail.com; 

Sampling date, Summer 2001; 

Sampling device, modified Livingstone piston corer (Wright et al. 1984); 

Diameter(cm), 8; 

Water depth(cm); 

Analysis method, "Sediments were collected from the center of each lake with two parallel, overlapping 8-cm diameter cores. Surface sediments (roughly <50 cm) were collected with a polycarbonate tube and the top 10-20 cm sliced at 0.5- 1.0 cm in the field. All cores had intermittent laminae, which were used to match records from overlapping segments of adjacent cores. Charcoal was identified at l(M0x magnification based on color, morphology, and texture. Charcoal concentrations (pieces per cubic centimeter) were multiplied by the estimated sedimentation rate (centimeters per year) to obtain the charcoal accumula- tion rate (CHAR, number of pieces per square centimeter per year) of each sample. Quantifying charcoal pieces instead of area was supported by empirical and theoretical studies linking fires with high charcoal counts (Whitlock and Millspaugh 1996, Gard- ner and Whitlock 2001, Gavin et al. 2003, Higuera et al. 2005, Peters and Higuera 2007) and by strong correla- tions between charcoal area and charcoal counts within individual records (Hallett and Walker 2000, Hallett et al. 2003). By using charcoal counts, we implicitly assumed that fragmentation of charcoal pieces was constant through time. For more details, including pollen analysis and record quality, please see Higuera_et_al_2009."; 

Instrumentation; 

Location description; 

Related NAPD, or Neotoma Pollen Chronology;