Forest fires were widespread throughout the US northern Rocky Mountains during the regional-fire years of 2000, 2003, 2006, and 2007.
However, until recently there was little knowledge of whether forest fires were also widespread in the past or of the role of climate in the occurrence of such years.
Emily K. Heyerdahl, Penelope Morgan, and Carol Miller
GOALS AND OBJECTIVES
Our objective was to address this knowledge using digital polygon fire atlases, fire scars on trees, and instrumental and tree-ring reconstructed climate. In addition, we modeled the landscape consequences of future fire regimes in this region, projected from changing climate.
Our fire atlas includes 5,038 fire polygons (digital fire perimeters) from 29,824,774 acres (12,070,086 hectares) that encompassed 71% of the forested land in Idaho and Montana west of the Continental Divide (12 national forests and one national park). Most of the area recorded as burned in the atlas from 1900 to 2003 (74%) occurred in just 11 regional-fire years. We reconstructed past fires from 9,245 fire scars from 576 trees on 21 sites across Idaho and western Montana and identified 32 years of widespread fire from 1650 to 1900. Fires were remarkably widespread during some of these years, including one year (1748) in which fires were recorded at ten sites across what are today seven national forests plus one site on state land.
We found that fire were widespread during certain years in the northern Rockies and that climate was and still is clearly associated with the occurrence of widespread fires throughout the 20th century and in prior centuries. Years of widespread fires had warm springs, followed by warm, dry summers. In addition, during the 20th century, widespread fires occurred during the positive phase of the Pacific Decadal Oscillation (PDO). A gap in years of widespread fire occurred during the mid-20th-century largely because climate conditions were generally not conducive for widespread fire. Given projections of future climate change, years of widespread fire are likely to continue to occur. However, simulation modeling results suggest that land management objectives can be met even with substantial increases in fire activity over 20th century levels.
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We acknowledge funding from the Joint Fire Science Program under Project JFSP 03-1-1-07. This project also received funding from RMRS and the University of Idaho.
PUBLICATIONS AND PRODUCTS
Heyerdahl, E.K., P. Morgan, and J.P. Riser II. 2008. Multi-season climate synchronized historical fires in dry forests (1650-1900), northern Rockies, USA. Ecology. 89:705-716.
Heyerdahl, Emily K.; Morgan, Penelope; Riser, James P., II. 2008. Crossdated fire histories (1650-1900) from ponderosa pine-dominated forests of Idaho and western Montana. Gen. Tech. Rep. RMRS-GTR-214WWW. Fort Collins, CO: US Department of Agriculture, Forest Service, Rocky Mountain Research Station. 83 p.
Miller, C. 2007. Simulation of the consequences of different fire regimes to support wildland fire use decisions. Fire Ecology. 3:83-102.
Morgan, P., E.K. Heyerdahl, and C.E. Gibson. 2008. Multi-season climate synchronized forest fires throughout the 20th century, northern Rockies, USA. Ecology. 89:717-728.
Shapiro-Miller, L.B., E.K. Heyerdahl, and P. Morgan. 2007. Comparison of fire scars, fire atlases, and satellite data in the northwestern United States. Canadian Journal of Forest Research. 37:1933-1943. A summary of this work was written in non-technical language and is available from the Joint Fire Science Program. (Morgan, P.; E. Heyerdahl; C. Miller. 2009. Climate and fire in the Northern Rockies: Past, present and future. Rachel Clark [editor]. Fire Science Brief. 32 [January]. 6 p. Available: http://www.firescience.gov/ [May 12, 2009].).
Our fire-scar dates and associated metadata are available from the International Multiproxy Paleofire Database with additional metadata publicly available from the RMRS Data Archive.