Las Bayas (LBA) - MXLBA001 Additional Site Information Emily K. Heyerdahl, Ernesto Alvarado Dating Method: Crossdated Sample Storage Location: USDA Forest Service, Rocky Mountain Research Station Fire Sciences Lab P.O. Box 8089 (or 5775 West Highway 10) Missoula, MT 59807 stored by Emily Heyerdahl (eheyerdahl@fs.fed.us, 406-829-6939) Reference: Heyerdahl, E.K. and E. Alvarado. 2003. Influence of climate and land use on historical surface fires in pine-oak forests, Sierra Madre Occidental, Mexico. Pages 196-217 in: Fire and climatic change in temperate ecosystems of the western Americas. eds. T.T. Veblen, W.L. Baker, G. Montenegro and T.W. Swetnam. New York: Springer-Verlag. Abstract: Our objective was to infer the drivers of temporal variation in fire regimes in pine-oak forests of the Sierra Madre Occidental in north central Mexico. We reconstructed a multicentury history (1772-1994) of the occurrence of surface fires from 1,469 fire scars on 180 trees sampled at 8 sites over approximtely 700 km in the states of Durango and Chihuahua. We compared our fire histories to existing tree-ring reconstructions of winter and early summer precipitation and the Southern Oscillation Index. Fire intervals were similar among our sites, with Weibull median fire intervals of 3 to 6 years. Most fires probably burned in the warm, dry spring, based on the intra-ring position of fire scars (formed during the season of radial dormancy or early in the growing season) and the seasonality of precipitation, lightning and modern fires in this region. However, some fall or winter fires may have occurred. Annual variation in precipitation and El Niņo/Southern Oscillation were strong drivers of current year's fire, probably through their effects on fuel moisture. Extensive fires generally burned during dry years but not during wet ones. Extensive fires also typically burned during La Niņa years, which tend to have dry winters in this region. Climate in prior years was also a strong driver of fire, through its effect on fuel amount. Widespread fires often burned following one to two wet years and also following El Niņo years, which tend to have wet winters in this region. Likewise, fires were not widespread following dry years and following La Niņa years. Prior year's climate probably affected the growth of grass and herbaceous fuel. Changes in land use, rather than climate, probably caused the near cessation of fire that we reconstructed at some sites because these shifts did not occur synchronously (some around 1900, some around 1950). Frequent surface fires continued to burn until the time of sampling at two of our sites. Individual Tree Species (Tree ID, description, species): LBA01,stump,unknown LBA02,snag,unknown LBA05,snag,unknown LBA07,stump,unknown LBA08,live,Pinus durangensis LBA09,live,Pinus ayacahuite LBA11,live,Pinus ayacahuite LBA12,stump,unknown LBA13,snag,Pinus teocote LBA14,live,Pinus durangensis LBA15,stump,Pseudotsuga menzisii LBA16,stump,unknown LBA19,snag,Pinus durangensis LBA20,live,Pinus durangensis LBA21,stump,unknown LBA22,stump,unknown LBA23,live,Pinus durangensis Fire History Graphs: Fire History Graphs illustrate specific years when fires occurred and how many trees were scarred. They are available in both PDF and PNG formats. The graphs consist of 2 parts, both of which show the X axis (time line) at the bottom with the earliest year of information on the left and the latest on the right. The Fire Index Plot is the topmost plot, and shows two variables: sample depth (the number of recording trees in each year) as a blue line along the left Y axis, compared with the percent trees scarred shown as gray bars along the right Y axis. Below, the Fire Chronology Plot consists of horizontal lines representing injuries by year on individual sampled trees. Symbols are overlain that denote the years containing the dendrochronologically-dated fire scars or injuries. The sample ID of each tree is displayed to the right of each line. The Composite Axis below represents the composite information from all individual series. The symbols used to represent the fire scars or injuries, and the filters used to determine the composite information, are shown in the legend. These graphs were created using the Fire History Analysis and Exploration System (FHAES). See http://frames.nbii.gov/fhaes/ for more information.