Climate Change Impacts on California Vegetation: Physiology, Life History, and Ecosystem Change

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.