Fire History Research

There are three global questions behind the fire history research being conducted in support of the WALTER project:

Based on historical information, what are the spatial and temporal patterns of human-caused ignitions and naturally caused fire ignitions?
What factors influenced these patterns?
How do these factors interact to produce particular types and levels of wildfire and of fire hazard?

To help address these questions and contribute to FCS-1, the model being developed, archival research is being conducted on documented fire occurrence and extent for the four project venues. The hard copy information will be digitized to help formulate a longer fire history record. Lightning strike and human caused ignitions will be evaluated relative to land use patterns in conjunction with the society research component. Tree ring data from a case study in the Rincon Mountains will be used to create an extensive, spatially explicit, long term fire history database. Analysis of these data should shed light on the influence of climate on wildfire patterns, and the influence of previous wildfires on the occurrence of future wildfires.

GIS-based modeling of fire history data provides an essential bridge that allows a combination of human dimensions and natural science components in the integrated model. Such spatial database development and mapping facilitates analysis of the relative contribution of humans and natural events to fire regimes in different ecosystems and allows analysis at different time and spatial scales.

Generating GIS map layers based on fire history data allows investigation of the linkages between climate variability and lightning activity in fire regimes and outcomes for ecosystems in the Southwest. Climate and fire history data, including lightning strikes, have been mapped at fine spatial scales for the past 20 years using existing tree-ring reconstructions of fire history. These reconstructions span the past 400 years, providing valuable contextual information about fire patterns and relative contributions of human and natural influences at longer time scales.

Dendrochronology
While recent fire history can be determined through records and satellite imagery, longer term information can obtained through dendrochronology, the dating and study of annual rings in trees.

chronology: the study of chronos (time), or more specifically events in past time

dendros: using trees, or more specifically the growth rings of trees, we can learn more about past events, including wildfire and changes in climate through study of tree ring growth.

Fire History
Fire-Scar Chronologies from Southwestern U.S. Forests

History Readings
Multicentury, tree-ring reconstructions of drought, disturbance history, and tree demography have been shown to reveal climatic effects across scales, from annual to decadal, and from local (100 km2) to mesoscale (10,000 to 1000,000 km2). Swetnam, T.W. and J.L. Betancourt. 1998. Mesoscale disturbance and ecological response to decadal climatic variability in the American Southwest. Journal of Climate 11(12): 3128-3148.

Tree Cross Section
A close-up of a cross section of a sugar pine from Sequoia National Park reveals a series of fire scars (Photo © A.C. Caprio). LTRR uses tree ring data to track historical environmental factors.

Andrew Ellicott
As early as 1894, Andrew Ellicott Douglass from the University of Arizona, noted that when viewing a cross section of a tree, it was shown in certain species that wide rings were produced during wet years, and narrow rings were produced during dry years. Between 1919 and 1936 while at the University of Arizona, he wrote Climate Cycles and Tree Growth (3 vols.).

Fire History, ENSO, & PDO
More recent tree-ring research suggests that wildfires in the Soutwest are linked to climate teleconnections, notably the El Niño-Southern Oscillation (ENSO) and the Pacific Decadal Oscillation (PDO) (Swetnam and Betancourt 1990; Simard et al. 1985: Grissino-Mayer and Swetnam 2000).