Fire history of a Douglas-fir-Oregon white oak woodland, Waldron Island, Washington

Abstract

The last 100 years have seen a marked decline in Oregon white oak woodlands in the Puget Sound region. Efforts to restore the woodlands cannot hope to be successful unless the role fire has played in maintaining them in the past is understood. A fire scar chronology was constructed from a Pseudotsuga menziesii-Quercus garryana community within a 155 ha study site on southeast Waldron Island, Washington. Sixty-two scars were identified on 15 crossdated Pseudotsuga samples that documented fire events between 1530 and 1908. A master tree-ring chronology was created for the period 1685 to 2004. Composite fire intervals and individual-tree fire intervals were used to characterize the fire history. Seasons of past fires were determined by analyzing fire scar position within annual ring structure. For the historical period 1700-1879, the composite mean fire return interval (FRI) was 7.4 yrs, and the mean individual-tree FRI was 18.4 yrs. The historic period mean individual-tree FRI was 18.4 yrs. In contrast, only three fires were recorded during the settlement/modern period (1880-2004), resulting in a mean individual-tree FRI of 103.8 yrs. Seasonality of past fires indicates that most fires occurred during late summer and fall. No evidence of spring or early summer burning was detected. Our study of the fire history for a site on Waldron Island shows a marked reduction in fire frequency between the historical and settlement/modern period, which we interpret as reflecting declines in Native American population size and activity and the eventual cessation of deliberate ignitions by Native Americans. © 2011 by the Northwest Scientific Association.