Tuesday, August 7, 2007 - 10:10 AMCOS 35-7: Using stand history to guide ecological restoration of a Garry oak/Douglas fir woodland
Peter W. Dunwiddie1, Jonathan D. Bakker2, Carson B. Sprenger2, and Mitchell Almaguer-Bay2. (1) The Nature Conservancy, (2) University of Washington
Ecological restoration activities guide future ecosystem development but require a clear understanding of site history. We used forest inventory and dendrochronological methods to examine the tree strata in a Garry oak (Quercus garryana) / Douglas-fir (Pseudotsuga menziesii) woodland on Waldron Island in the San Juan Islands, Washington. This ecosystem is relatively uncommon and of significant conservation interest in the Pacific Northwest. Prior to Euro-American settlement in the 1880s, an open woodland/savanna was maintained by fires, likely set by Native Americans, with a return interval of 7.4 years. Historical stand structure was roughly 100 trees/ha, with a ratio of Douglas-fir to Garry oak stems < 1:1. Small (< 20 cm DBH) Douglas-fir trees established throughout the last century, particularly between 1970 and 1982. As a result, the stand contained 999 trees/ha and a 10:1 Douglas-fir / Garry oak ratio in 2006. Factors responsible for these changes include the long-term exclusion of low-intensity surface fires, selective logging, and the cessation of sheep grazing. By 2006, young Douglas-firs were overtopping the established Garry oaks and increasing the mortality of this rare ecosystem component. Based on these data, we established a management objective of modifying the stand to more closely resemble the structure and composition that occurred prior to Euro-American settlement. The management prescription focused on releasing the mature oaks by cutting and burning many (93%) of the young Douglas-firs. Future management will be directed towards restoring understory components of this system, as well as potentially reintroducing historically significant processes such as surface fire.