The Influence of Hydroclimate and Silvicultural Treatment on Rates of Forest Regrowth Following Harvest across the Western U.S.

Abstract:

Identifying appropriate forest management strategies to promote forest health, while maintaining important ecosystem services remains a challenge for forest ecologists and managers. Forests of the western U.S. have been subjected to a range of management intensities, but it is still unclear which silvicultural treatments produce the most rapid rates of forest regrowth across complex terrain that exhibit significant gradients in water and energy availability. We analyzed trends in net primary productivity (NPP) for 36,233 individual silvicultural treatments at a 30m resolution and assessed rates of NPP recovery following harvest across the western U.S. We found that differences in the climatic water balance were a strong driver of forest regrowth rates across the majority of treatment types. Rates of regrowth ranged from 2.02 gC m^-2 y^-2 in dry landscape positions with high annual climatic water deficits (e.g. southerly aspects, low elevation, continental interior) to 9.13 gC m^-2 y^-2 in wet landscape positions (e.g. northerly aspects, high elevation, coastal settings). In wet landscapes clear cutting and shelterwood harvesting yielded the fastest rates of regrowth. In arid landscapes shelterwood harvests exhibited the fastest rates of regrowth, while clear cutting harvests exhibited the slowest rate of regrowth indicating the potential for ecosystem state shifts with increasing aridity. These results highlight the critical role of stand structure and microclimates for seedling establishment and growth in more xeric climates. In aggregate, this study provides a template for understanding forest regrowth dynamics following harvest across the large climatic gradient and a multitude of treatment options that managers employ in western U.S. forests.