Historical and current forest landscapes in eastern Oregon and Washington. Part II: Linking vegetation characteristics to potential fire behavior and related smoke production

We compared the potential fire behavior and smoke production of historical and current time periods based on vegetative conditions in forty-nine 5100- to 13 5OO-hectare watersheds in six river basins in eastern Oregon and Washington. Vegetation composition， structure， and patterns were attributed and mapped from aerial photographs taken from 1932 to 1959 (historical) and from 1981 to 1992 (current). Vegetation with homogeneous composition and structure were delineated as patches. Each patch was assigned a potential rate of spread， flame length， fuel loading， and smoke production from published information that matched the closest characteristics of the vegetation and downed fuels and assigned a uniform fuel moisture， wind speed， and slope. Potential rate of spread of fire， flame length， and smoke production were highly variable among sample watersheds in any given river basin. In general， rate of spread and flame length were positively correlated with the proportion of area logged in the sample watersheds. There were large increases in potential smoke production from the historical to the current periods for many sample watersheds due to changes in fuel loadings associated with management activities and， presumably， fire suppression. Wildfires were shown to produce nearly twice the amount of smoke as prescribed fire for the current period for all river basins. Understanding these and other tradeoffs will assist managers and society in making informed decisions about how to implement prescribed fire and manage wildfire to address air quality and forest health problems. Because of the variability of fuel or vegetative conditions observed among the sample watersheds， we recommend an extensive characterization of these conditions before large-scale restoration and maintenance of fire-related processes are undertaken.