Archuleta Mesa Plot D2 - USACH022 Additional Site Information Peter M. Brown, Rosalind Wu Dating Method: Crossdated Sample Storage Location: Rocky Mountain Tree-Ring Research, Inc., Ft. Collins, CO Reference: P.M. Brown & R. Wu. 2005. Climate and disturbance forcing of episodic tree recruitment in a southwestern ponderosa pine landscape. Ecology 86:3030-3038. Abstract: Strong but relatively short (annual to decadal length) climate change can have broad-scale and long-lasting effects on forest communities. Climate impacts forests through direct effects on tree demography (mortality and overstory recruitment) and indirect effects on disturbance regimes. Here, we compare multicentury chronologies of tree recruitment from a 307-ha ponderosa pine forest in southwestern Colorado to reconstructions of fire years, hydroclimate, and the El Nino-Southern Oscillation (ENSO). Few trees predate a regional multiyear megadrought centered in the 1580s. A prolonged pluvial in the early 1600s resulted in a pulse of tree recruitment that corresponds to recruitment seen over much of the Southwest. Other cohorts in the early 1700s and mid-1800s established during multidecadal fire- quiescent periods. These periods correspond to shifts in ENSO that apparently resulted in dampening of interannual wet/dry oscillations responsible for fuel buildup and drying. Fires, mediated by stochastic climate variation, acted as a density independent regulation on tree populations since establishment was not limited by overstory tree density, but rather by fire-caused mortality of seedlings and saplings during periods of more frequent fires. Even-aged cohorts in ponderosa pine forests likely have little if anything to do with episodic mortality caused by more severe fires, but rather relate mainly to episodic recruitment opportunities. Fire cessation after Euro-American settlement in the late 1800s resulted in an increase in tree density and changes in forest composition, which are major factors that have contributed to recent severe wildfires in other Southwestern forests. Our results document clear linkages between synoptic climate forcing, fires, and recruitment episodes, and highlight the importance of regional historical processes on contemporary forest composition and structure. Establishment date data from this site are available at: ftp://ftp.ncdc.noaa.gov/pub/data/paleo/firehistory/establishment/northamerica/usach022.dat Comments: The "." and "|" symbols were not used in the standard manner as described in the FHX2 users manual, in that they do not indicate whether or not a year is considered a "recorder" year. Rather, the "|" symbol is used to indicate that a dated ring was present, while the "." symbol is used to indicate that no dated ring was present (typically before and after the age range of the tree as well as between an estimated pith date and the earliest ring that was present). 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.