DEVELOPMENT OF A PONDEROSA PINE TREE-RING CHRONOLOGY AND FIRE RECORD FOR THE BOISE FRONT, BOISE, IDAHO

Fires and fire-related sedimentation events along the Boise Front are not a new problem, A lack of understanding, though, of the relationship between wildfire and climate coupled with residential development encroaching into drainages headed in the wooded foothills could create a scenario of future increased damage from fire-related flooding. Identification of fire recurrence and the influence of climate on fire in the Boise Front is limited to scattered records starting early in the early 20th century. To extend that record and to better understand the variability of fire recurrence, a tree-ring chronology from ponderosa pine in a south-facing slope in the Shafer Creek drainage (16 km N of Boise) has been developed back to 1703. Initial analysis of the ARSTAN chronology with various climate records suggests the dominant influence on tree-ring variability is early water year (October to May) precipitation, with similarly significant correlations to reconstructed PDSI, both indicating precipitation as the primary factor in tree growth. During collection of the increment cores, several fire-scarred trees within a half mile of each other in the same drainage were identified and partial sections were removed using a chainsaw and the sections cross-dated to the cores. Two trees both recorded fires in 1880, 1832, and 1772, with one of those trees also recording three earlier fires in the 18th century. All fires appear to have occurred during the trees' dormant period. Comparing the limited records provided by these scars to PDSI data suggest that fires in the 1700's were coincident with or in the years immediately following moderate to severe droughts, but that fires in the 1800's occurred in very moist years. The timing and extent of fires in the Shafer Creek drainage and the influence of climate on their recurrence is compared to several fire scar records subsequently collected in the Dry Creek drainage (3 km south of Shafer Creek site). Together, these tree-ring and fire records provide a basis for understanding the relationship between climate and fire along the Boise Front, and subsequently the relationship between fire and flood hazards to developments downslope.