Date Published: January 25, 2019
Publisher: Public Library of Science
Author(s): Tim Sheehan, Dominique Bachelet, Ken Ferschweiler, Debjani Sihi.
To develop effective long-term strategies, natural resource managers need to account for the projected effects of climate change as well as the uncertainty inherent in those projections. Vegetation models are one important source of projected climate effects. We explore results and associated uncertainties from the MC2 Dynamic Global Vegetation Model for the Pacific Northwest west of the Cascade crest. We compare model results for vegetation cover and carbon dynamics over the period 1895–2100 assuming: 1) unlimited wildfire ignitions versus stochastic ignitions, 2) no fire, and 3) a moderate CO2 fertilization effect versus no CO2 fertilization effect. Carbon stocks decline in all scenarios, except without fire and with a moderate CO2 fertilization effect. The greatest carbon stock loss, approximately 23% of historical levels, occurs with unlimited ignitions and no CO2 fertilization effect. With stochastic ignitions and a CO2 fertilization effect, carbon stocks are more stable than with unlimited ignitions. For all scenarios, the dominant vegetation type shifts from pure conifer to mixed forest, indicating that vegetation cover change is driven solely by climate and that significant mortality and vegetation shifts are likely through the 21st century regardless of fire regime changes.
Expected ecosystem responses to climate change include altered fire regimes (e.g. [1–3]), insect outbreaks (e.g. ), hydrologic changes (e.g. ), altered nutrient cycling (e.g. ), species range shifts (e.g. [7–9]), and novel species assemblages (e.g. [10–11]). Vegetation models have been used to simulate such changes and provide resource managers projections to help their decision process . Estimating associated uncertainty allows managers to modulate their strategies .
For the area west of the Cascade Crest in Oregon and Washington, we found assumptions about CO2 fertilization effects and fire occurrence in the MC2 DVGM have substantial effects on simulated carbon dynamics. Without fire, CO2 fertilization increases C stocks, while the lack of CO2 fertilization leads to decreases in C stocks. For scenarios with fire, CO2 fertilization mitigates projected C losses due to fire, limiting decreases over the 20th and 21st centuries by a factor of 4 versus scenarios without CO2 fertilization.