Forest restoration thinning accelerates development of old‐growth characteristics in the coastal Pacific Northwest, USA

Abstract A century of industrial‐scale management has transformed vast swaths of forest land across the Pacific Northwest (PNW), USA, from ancient forests with complex structure and diverse habitats to young forests with simple structure and dominated by few species. Consequently, there have been calls to restore ecosystem integrity and resilience. Here, we apply data from a watershed‐scale experiment to determine if restoration treatments have achieved our management goal of accelerating the development of old‐growth forest characteristics. We provide empirical evidence of how restoration treatments have affected key old‐growth forest indicators resulting in larger trees, more complex vertical and horizontal forest structure, reduced stand density, and increased understory plant richness. Our study also demonstrates that some restoration indicators responded in counter‐intuitive ways contingent on interactions between stand age and restoration treatment. Through this work, we learned two important lessons: (1) more time and monitoring may be needed to fully understand the effects of restoration treatments and (2) a “one and done” approach of implementing restoration treatments may not achieve a full suite of old‐growth characteristics. Moreover, long‐term management for wildlife habitat and climate resilience will likely require an adaptive approach, with ongoing monitoring continually informing and adjusting management practices.