39 Mile Mountain - US39M001 Additional Site Information Joseph A. Donnegan, Thomas T. Veblen, and Jason S. Sibold Dating Method: Crossdated Sample Storage Location: Biogeography Lab, Department of Geography, University of Colorado, Boulder, CO, USA Reference: Donnegan, J.A., T.T. Veblen and J.S. Sibold. 2001. Climatic and human influences on fire history in Pike National Forest, central Colorado. Canadian Journal of Forest Research 31: 1526-1539. Abstract: We investigated inter-annual and multi-decadal variability in fire regimes, as related to climate and human land-use in Pike National Forest, central Colorado. Short and long-term trends in fire-scar records were related to tree-ring proxy records of moisture availability and to variability in El Niņo-Southern Oscillation (ENSO). Fire occurrence is strongly tied to inter-annual drought conditions and is associated with cycles of ENSO. Fire events tend to occur in years of reduced moisture availability (La Niņa years), and are often preceded by 2-4 years of increased moisture availability (El Niņo years). A period of reduced variability in the tree-ring record from 1760 to 1820 A.D., roughly corresponds to a period of reduced fire occurrence from approximately 1792 to 1842. Coincident with increased fire occurrence, variability in the climate proxies was high in the mid- to late-1800s until the early 1900s. Multi-decadal impacts through land use are also evident in the fire record with sharp increases during Euro-American settlement in c. 1850 and abrupt declines with the start of active fire suppression after c. 1920. Both humans and climatic variation appear to have interacted synergistically to create long-term trends in fire occurrence over the past two centuries. 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.