Peters Flat - USPET001 Additional Site Information Henri D. Grissino-Mayer, Thomas W. Swetnam, and Christopher H. Baisan Dating Method: Crossdated Related ITRDB Chronology: az549.crn Sample Storage Location: Laboratory of Tree-Ring Research, University of Arizona, Tucson, AZ. Reference: Grissino-Mayer, H.D., Baisan, C.H., and T.W. Swetnam. 1995. Fire history in the Pinaleņo Mountains of southeastern Arizona: Effects of human-related disturbances. In: L.F. Debano, G.J. Gottfried, R.H. Hamre, C.B. Edminster, P.F. Ffolliott, and A. Ortega-Rubio, eds., Biodiversity and Management of the Madrean Archipelago: The Sky Islands of Southwestern United States and Northwestern Mexico. USDA Forest Service General Technical Report RM 264: 399-407. Swetnam, T. W. and C. H. Baisan. 1996. Fire histories of montane forests in the Madrean Borderlands. In P. F. Ffolliott et al. tech. coords., Effects of fire on Madrean Province Ecosystems, A symposium proceedings, USDA Forest Service General Technical Report RM-GTR-289: 15-36. Swetnam, T. W., Baisan, C.H. and J. M. Kaib. 2001. Chapter 7: Forest fire histories in the sky islands of La Frontera. In G. L. Webster and C. J. Bahre eds., Changing Plant Life of La Frontera: Observations on Vegetation in the United States/Mexico Borderlands. University of New Mexico Press, Albuquerque: 95-119. Abstract: (Grissin-Mayer et al., 1995) We reconstructed the history of fire at two sites in the mixed-conifer forests of the Pinaleno Mountains of southern Arizona from 90 fire-scarred living and dead southwestern white pine (Pinus strobiformis) and ponderosa pine (Pinus ponderosa) trees. We used dendroecological techniques to date nearly 2000 fire scars to their exact year of formation, and obtained age structure information from over 600 increment cores and cross-sections collected from Engelmann spruce (Picea engelmannii) and corkbark fir (Abies lasiocarpa). We compared the age structure data with the reconstruction of past fires to determine which fires may have had an effect on the higher-elevation forests. During the pre-settlement period (prior to 1880), low-intensity surface fires occurred once every four to six years, based on the median probability interval derived using the Weibull distribution. The age structure of the spruce-fir forest suggests that the forest established after a stand-replacement fire that occurred in 1685, considered one of the most widespread and intense of any reconstructed fire event. Fires had occurred predominantly in the early portion of the growing season (May and June) similar to current dominant season of fire activity. The cessation of episodic fires after 1893 can be attributed to a combination of human-related disturbances, especially grazing and fire exclusion. The absence of ecologically-significant fires during the last 100 years in the Pinaleno Mountains should be considered when developing land and fire management plans for this environmentally sensitive area. 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.