California Institute for Energy and Environment (CIEE)

Dominant plant species mediate many ecosystem services, including carbon storage, soil retention, and water cycling. One of the uncertainties with climate change effects on terrestrial ecosystems is understanding where transitions in dominant vegetation, often termed state change, will occur. The complex nature of state change requires multiple lines of evidence. Here, we present four lines of inquiry into climate change effects on dominant vegetation, focusing on the likelihood and nature of climate change–driven state change. This study combined physiological measurements, geographic models, historical documented cases of state change, and statewide plot sampling networks together with interpolated climate grids. Together these approaches suggest that the vulnerability to state change will be driven by the proximity of climatic conditions to biological thresholds for dominant species. The sensitivity of the dominant species is a much greater driver of climate vulnerability compared to the degree of climate change seen by a particular place (Section 1). Furthermore, in some cases, physiological measurements on those species can inform the nature of these thresholds (Section 3). The study team’s review of past state change events suggests connections between particular state changes (e.g., forest to shrubland) and particular triggers (e.g., fire; Section 2). The effect of fire is particularly important, as it will likely interact with climatic change with implications for the success of different life history strategies among woody plants (Section 4). Our work suggests that the biological thresholds of dominant species will play a crucial role in the vulnerability of California terrestrial ecosystems. Understanding where climate change will push dominant species past these thresholds should be a major focus of future research.