Skip to Main Content
U.S. Forest Service
Caring for the land and serving people

United States Department of Agriculture

Home > Search > Publication Information

  1. Share via EmailShare on FacebookShare on LinkedInShare on Twitter
    Dislike this pubLike this pub
    Author(s): Christopher D. O'Connor; Donald A. Falk; Ann M. Lynch; Thomas W. Swetnam
    Date: 2014
    Source: Forest Ecology and Management. 329: 264-278.
    Publication Series: Scientific Journal (JRNL)
    Station: Rocky Mountain Research Station
    PDF: Download Publication  (1.18 MB)


    In recent decades fire size and severity have been increasing in high elevation forests of the American Southwest. Ecological outcomes of these increases are difficult to gauge without an historical context for the role of fire in these systems prior to interruption by Euro-American land uses. Across the gradient of forest types in the PinaleƱo Mountains, a Sky Island system in southeast Arizona that experienced two relatively large high-severity fires in the last two decades, we compared fire characteristics and climate associations before and after the onset of fire exclusion to determine the degree of similarity between past and recent fires. We use a gridded fire scar and demography sampling network to reconstruct spatially explicit estimates of fire extent and burn severity, as well as climate associations of fires from individual site to landscape scales from 1640 to 2008 C.E. We found that patterns of fire frequency, size, and severity were relatively stable for at least several centuries prior to 1880. A combination of livestock grazing and active fire suppression after circa 1880 led to (1) a significant reduction in fire spread but not fire ignition, (2) a conversion of more than 80% of the landscape from a frequent, low to mixed-severity fire regime to an infrequent mixed to high-severity fire regime, and (3) an increase in fuel continuity within a mid-elevation zone of dry mixed-conifer forest, resulting in increased opportunities for surface and crown fire spread into higher elevation mesic forests. The two most recent fires affecting mesic forests were associated with drought and temperature conditions that were not exceptional in the historical record but that resulted in a relative proportion of high burn severity up to four times that of previous large fires. The ecological effects of these recent fires appear to be more severe than any fire in the reconstructed period, casting uncertainty upon the recovery of historical species composition in high-severity burn patches. Significant changes to the spatial pattern, frequency, and climate associations of spreading fires after 1880 suggest that limits to fuel loading and fuel connectivity sustained by frequent fire have been removed. Coinciding factors of high fuel continuity and fuel loading, projected lengthening of the fire season, and increased variability in seasonal precipitation suggest that large high-severity fires, especially in mixed-conifer forests, will become the predominant fire type without aggressive actions to reduce fuel continuity and restore fire-resilient forest structure and species composition.

    Publication Notes

    • You may send email to to request a hard copy of this publication.
    • (Please specify exactly which publication you are requesting and your mailing address.)
    • We recommend that you also print this page and attach it to the printout of the article, to retain the full citation information.
    • This article was written and prepared by U.S. Government employees on official time, and is therefore in the public domain.


    O'Connor, Christopher D.; Falk, Donald A.; Lynch, Ann M.; Swetnam, Thomas W. 2014. Fire severity, size, and climate associations diverge from historical precedent along an ecological gradient in the Pinaleno Mountains, Arizona, USA. Forest Ecology and Management. 329: 264-278.


    Google Scholar


    spatial reconstruction, fire history, elevation gradient, ENSO, PDSI, climate

    Related Search

    XML: View XML
Show More
Show Fewer
Jump to Top of Page