Post disturbance tree establishment in mature Douglas-fir forests in Washington and Oregon

Background/Question/Methods

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 age classes of mature stands (stand age 80-200 years) with a rigorous sampling of tree cores. In this study we characterized temporal patterns of Douglas-fir trees in mature Douglas-fir stands throughout the Cascade Mountain Range in Washington and Oregon.  Increment core samples were collected from n=12 sites throughout the western Cascades of Washington and Oregon. 40-70% of Douglas-fir trees were sampled in each site. Annual rings were counted, and center dates were determined to examine within-site age variation.

Results/Conclusions

 
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 was variable among sites and occurred over several decades. Rapid natural forest regeneration occurring over several decades facilitates persistence of open canopy 
conditions and extends the developmental period characterized by early seral communities and processes. Patterns of tree regeneration following natural disturbance events 
can provide insight into multiple developmental pathways which can potentially guide management of post-disturbance forest ecosystems.