Projecting the effects of climate change and management in forests of the Puget Sound Lowlands

Open Access
Laflower, Danelle M
Graduate Program:
Master of Science
Document Type:
Master Thesis
Date of Defense:
May 06, 2015
Committee Members:
  • Matthew David Hurteau, Thesis Advisor
  • Pacific Northwest
  • forests
  • climate change
  • carbon sequestration
  • management
  • Oregon white oak
Tree species have differential responses to changing climate, which may affect competitive interactions and alter species composition and forest carbon dynamics. In energy-limited systems, warming temperatures may lengthen growing season and increase water demand. In water-limited systems, increased evapotranspiration associated with warmer temperatures may limit species diversity and productivity. Management may help maintain productivity under changing climate by reducing competition for resources, increasing heterogeneity, and decreasing disturbance risk. I sought to quantify how projected changes in climate may alter the composition and productivity of Puget Lowland forests, and how management could mitigate changes. I also sought to determine the effects of management on, and carbon tradeoffs of, restoring oak woodland habitats. I used a simulation approach to model four landscape-scale treatments (control, burn only, thin only, thin and burn) using current climate and projected climate for two general circulation models (CCSM 4 and CNRM-CM5), driven by two emission scenarios (moderate (RCP 4.5) and high (RCP 8.5) emissions) at Joint Base Lewis-McChord, Washington. At the landscape-scale, I found little difference in carbon dynamics and species composition under the moderate emission scenarios. However, by late-century under the high emission scenario, I found substantial declines in productivity due to a decrease in late-successional species growth. The major effect of management was to increase net ecosystem carbon balance after 2030, relative to the control. Relative to 2012, I found the frequency of sites that were likely to contain Oregon white oak decreased over time under all treatments, regardless of climate. To counteract the decline, I added an intensively managed 708 ha oak restoration area (2% of the landscape) to the landscape-scale thin and burn treatment. Relative to the thin and burn treatment, the intensive management increased oak presence and incurred small initial carbon costs (<400 g C m-2) that decreased over time. My research suggests that under the late-century high emission scenario, management cannot alter the climate-driven decline of late-successional species, but intensive management can alter forest structure, which may increase species richness and help alleviate declines in productivity.