Thursday, August 7, 2008: 3:20 PM
103 DE, Midwest Airlines Center
Background/Question/Methods Fire is a primary natural disturbance in the Siskiyou Mountains of the Pacific Northwest, but recent severe fire episodes reopened the debate over management options before and after fire (e.g. savage logging, fire suppression). Managing such flammable ecosystems represents a major challenge for many agencies, although the observational record does not adequately characterize the variability of fire disturbance over time. Thus, paleoecological methods integrate modern ecological observations, by providing unique long-term data for reconstructing disturbance regimes over time. We use combined series of pollen, charcoal and sedimentological data from a ca. 2000-year record from Little Squaw Lake (Applegate Valley, Southern Oregon) to understand: 1) the long term vegetation dynamics around the site since the Medieval Warm Period 2) the response of forest ecosystems under natural fire regimes 3) the effect of 40 years of logging on species composition and on soil stability.
Results/Conclusions Our results show a significant link between fire, vegetation dynamics, and erosional processes. Taxus, Cupressaceae and understorey taxa (e.g. Corylus, Rubus) were more important before the settlement period, suggesting that overall, forests were fairly dense prior to today’s higly disturbed ecosystems. In particular, for the Medieval time period, peaks of charcoal concentration are related to high values of Pinus cf. ponderosa and Pseudotsuga menziesii, a situation that is similar to the present day highly disturbed forests. Charcoal analyses together with magnetic susceptibility reveal minor but distinct erosion episodes following individual fires, suggesting fire events were severe enough to affect soil stability. However, this effect has increased significantly after logging commenced in the watershed, probably due to more fire disturbance and road construction on steep slopes. Our results suggest that high severity fires are not a recent phenomenon in this region, but rather that dense forests existed over long periods of time. Furthermore, assessing the long-term sensitivity of species to fire provides information about possible future scenarios, assuming that climate change will affect the intensity and frequency of fire events. In this sense this study offers a better insight into natural processes that occurred prior to the impacts of extensive forest management, in a region that is regarded for its high values of biodiversity and endemic species.
Results/Conclusions Our results show a significant link between fire, vegetation dynamics, and erosional processes. Taxus, Cupressaceae and understorey taxa (e.g. Corylus, Rubus) were more important before the settlement period, suggesting that overall, forests were fairly dense prior to today’s higly disturbed ecosystems. In particular, for the Medieval time period, peaks of charcoal concentration are related to high values of Pinus cf. ponderosa and Pseudotsuga menziesii, a situation that is similar to the present day highly disturbed forests. Charcoal analyses together with magnetic susceptibility reveal minor but distinct erosion episodes following individual fires, suggesting fire events were severe enough to affect soil stability. However, this effect has increased significantly after logging commenced in the watershed, probably due to more fire disturbance and road construction on steep slopes. Our results suggest that high severity fires are not a recent phenomenon in this region, but rather that dense forests existed over long periods of time. Furthermore, assessing the long-term sensitivity of species to fire provides information about possible future scenarios, assuming that climate change will affect the intensity and frequency of fire events. In this sense this study offers a better insight into natural processes that occurred prior to the impacts of extensive forest management, in a region that is regarded for its high values of biodiversity and endemic species.
