How will changes in air temperature and precipitation amounts affect the growth Douglas-fir, a dominant species throughout much of the Pacific Northwest? While ecological succession shapes contemporary forest structure and dynamics, other factors like forest structure (dense vs. sparse canopies) and climate may alter structural trajectories. David Bell and Andrew Gray, scientists with the Pacific Northwest Research Station examined how the proportion of biomass accumulation differed in Douglas-fir across vegetation zones representing broad gradients in precipitation and temperature. Specifically, they examined three potential drivers of biomass change: structural status of the stand, forest canopy status, and climate based on data from 3510 forest inventory plots in Oregon and Washington.
They found Douglas-fir biomass in wet forests not only increased in early-developmental stands (low biomass and high density), but also in late-developmental stands, defined by few, large trees, especially for the warmer zone. This highlights the potential for continued atmospheric carbon sequestration in warm and wet forests of the Pacific Northwest for both young and old forests, given that future climatic conditions support similar forest dynamics. However, accumulations of forest biomass in areas that become warmer and drier may be more limited. Their results suggest that shifting climate that alters the geographic distribution of warm vs. cool and wet vs. dry landscapes could dramatically change Douglas-fir biomass dynamics and alter regional species dominance.