Long-term Response of Coastal Forests to Wind Disturbance

Mark Harmon and Rob Pabst have authored a new paper in a special issue of the journal Forests on wind disturbance (http://doi.org/10.3390/f10020119).  Harmon and Pabst took advantage of tree measurements spanning 78 years in ten plots at Cascade Head Experimental Forest to examine the cumulative effects of wind disturbance on forest structure, tree mortality, and net primary productivity.  This set of permanent plots was established in 1935 for the purpose of understanding growth and yield of coastal forests dominated by western hemlock and Sitka spruce.  However, since 1951 the plots have experienced hurricane-force winds at least ten times, providing an opportunity to examine long-term response of coastal forests to wind.  Not all plots were substantially impacted by all the storms; rather, the major wind events had differential effects on the plots, suggesting that wind impacts at a broader landscape level are cumulative over time.  Key findings include: (1) the proportion of wind-related tree mortality has increased 5- to 8-fold since 1940, and (2) despite the increase in wind-related tree mortality over time, impacts to net primary productivity were only noticeably when biomass loss exceeded 50%.  The long-term nature of this and other permanent plot research offer poignant lessons in how repeated observations over long time periods help us understand how and why forests change.

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