GC33D-0544:
When a Refuge is No More: Higher than Expected Wildfire Severity in Historical Forest Refugia
Wednesday, 17 December 2014
Tyler Bleeker1, Crystal Kolden1, Ann E Camp2, Paul F Hessburg Sr3 and Helen Poulos4, (1)University of Idaho, Moscow, ID, United States, (2)Yale University, School of Forestry and Environmental Studies, New Haven, CT, United States, (3)USDA-Forest Service, Wenatchee, WA, United States, (4)Wesleyan University, College of the Environment, Middletown, CT, United States
Abstract:
Global climate change is an increasingly important driver of changes in the biogeograpraphy of vegetation. Such changes have primarily been characterized by gradual shifts in species distribution; however, major disturbances acting in concert with climate change may result in a sudden ‘jump’ in biogeographical distribution. This study examines the effects of wildfire on forest composition along an environmental gradient in the eastern Cascade Mountains of Central Washington, USA. A previous study by Camp et al. (1997) examined three drainages in this complex mountainous landscape to identify and characterize historic wildfire refugia based on topographic characteristics and forest age and species composition. These drainages subsequently burned in the 2012 Table Mountain and Peavine Canyon fires. In 2014 the Camp et al. plots were re-established and re-sampled to (1) assess burn severity using the Composite Burn Index (CBI) protocol and (2) assess fire effects upon the individual trees in each study plot. Remotely sensed imagery classified using the differenced Normalized Burn Ratio (dNBR) indicated these fires burned more intensely than historical fires in the region, providing a potential harbinger of future fire severity under climate change. Analysis of burn severity revealed that the fire burned across the entire environmental gradient of the drainages, with no significant difference in burn occurrence or burn severity between refugial and non-refugial plots as designated by Camp et al.; this suggests that historical wildfire refugia may no longer prove sustainable in an era of climate change. Additionally, trees characteristic of warmer and drier climates experienced lower fire mortality than trees typical of cooler and moister climates. If future reseeding and recruitment in the forest favors more xeric tree species, the 2012 fires may prove to be the disturbance event that precipitates a ‘jump’ in the biogeographic distribution of trees in these drainages.
