The role of disturbances in mediating ecosystem responses to climate changes: Lessons from a diversity of landscapes
Disturbance regimes, and their sensitivity to climate, may alter the spatial and temporal responses of vegetation to climate change because disturbances can shape total ecosystem biomass, species assemblages, and biogeochemical processes. Consequently, as climate changes in the future, ecosystem responses may depend on local disturbances and the responses of the disturbances to climate. Here, we evaluate the hypothesis that disturbance-prone ecosystems, such as fire-dominated lodgepole pine forest of the Rocky Mountains, prairie-woodland ecotones of the Great Plains, and human-occupied forests of New England, have been less responsive to long-term climate changes over the past 15,000 years than other settings. To do so, we use dissimilarity metrics to measure past vegetation changes based on fossil pollen assemblages from several North American settings, and compare these metrics with past magnitudes of climate change and past fire regimes. Fire history is reconstructed using sedimentary charcoal records.
Dissimilarity metric from a wide network of Rocky Mountain sites show dramatically less vegetation change in these fire-dominated ecosystems than at eastern North American sites where fire has been less common. Eastern pollen records commonly reveal that climate changes produced ecosystem responses of the same magnitude as the ecosystem changes associated with European land-clearance; such large changes are uncommon in the Rocky Mountains. However, exceptions in the east, such as Crooked Pond in Plymouth, Massachusetts, and Minnetoga Pond in Minneapolis, Minnesota, reveal that frequent fire in human occupied landscapes of the east also dramatically reduced responsiveness to past climate change. Complex vegetation-fire-climate interactions on the prairie-forest ecotones both in the Rocky Mountains and in Minnesota point to the possibilities of multiple steady states in disturbed settings. Taken together, the results reveal the importance of disturbance as a mediator of climate-vegetation interactions.