Establishment history of mature Douglas-fir forests in the southwest Washington Cascade Range

Stand reconstructions of natural old-growth (stand age >200 years) Douglas-fir forests have documented both rapid (< 100 year) and prolonged (>100 year) initial establishment periods for the pioneering post-disturbance cohort of Douglas-fir. Few studies have examined the duration of Douglas-fir establishment in other age classes of mature stands (stand age 80-200 years). In this study we characterized temporal patterns of Douglas-fir trees in 200 year old stand located in the south west Washington Cascade Range. Increment core samples were collected from two hundred ninety-one Douglas-fir trees distributed across n = 7 study sites. Thirty to sixty increment core samples were taken from each of 7 sites. Annual rings were counted, and center dates were determined to examine within-site age variation. All sites experienced a narrow range (<100 years) of establishment indicating a rapid initial establishment of Douglas-fir. However, establishment of the pioneer Douglas-fir cohort occurred over several decades. Rapid natural forest regeneration occurring over several decades facilitates persistence of open canopy conditions and creates early seral communities. Conversely, modern forest management practices that replant one to two years following disturbance can attain closed canopy conditions within one decade. These results indicate uniform patterns of tree regeneration across the study area. Patterns of tree regeneration following natural disturbance can potentially guide management of post-disturbance forest ecosystems.