A RECONSTRUCTION OF FIRE HISTORY USING MACROSCOPIC CHARCOAL ANALYSIS: FISH LAKE, SINLAHEKIN WILDLIFE AREA, NORTH CENTRAL WASHINGTON, USA.

The Sinlahekin Wildlife Area is a 14,000 acre reserve located in the Okanogan Valley of north central Washington. Sitting in the rain shadow of the Cascade Mountains, its forests consist primarily of ponderosa pine (Pinus ponderosa), which are adapted to frequent lowseverity fires. However, because of fire suppression over the past approximately 100 years, fire has all but disappeared from this ecosystem. As a consequence, excess biomass has accumulated on the forest floor, leading to catastrophic forest fires. To better understand the current dilemma, a long-term perspective on fire history is needed. Lakes hold much information on fire history in the form of fossilized charcoal. Identifying changes in charcoal accumulation in lake sediments allows for a calculation of past fire frequency. This information can then be used as a guideline for prescribed burning and managing forest health. In summer 2011, a 3 meter long sediment core was retrieved from Fish Lake in the Sinlahekin Wildlife Area. Macroscopic charcoal analysis was used to reconstruct fire history for the last 2500 years. Loss on ignition and magnetic susceptibility were also used to characterize the lithology of the core and to investigate the relationship between fire and erosional events. Results show that fire activity was high at the site prior to the last century. Fires burned mainly herbaceous material (i.e. grass), indicating that fires were low-severity. Further analysis of the core, including pollen analysis, will highlight the relationship between fire and vegetation change, human activity, and regional climate change.