JUSTIN M. VALLIERE, Ph.D.
Assistant Professor of Cooperative Extension
University of California Davis
How can we restore California's native plant communities in the face of invasion and environmental change?
I am a plant ecologist whose research is motivated by a lifelong fascination in plants and a passion for conservation. Multiple drivers of global change, such as biological invasions, nitrogen (N) deposition, and climate change pose a significant and growing threat to native ecosystems. A major challenge in conservation also continues to be bridging the gap between science and management. The goal of my research is to explore the impacts of human-caused global change on native plant communities, identify mechanisms of change, and inform land management and restoration. By studying disturbed and novel ecosystems, I aim to better understand the processes driving community assembly, while building on our capacity to predict changes under future global change. My research approach integrates biogeochemistry, community ecology, ecophysiology and soil ecology, and I utilize observational studies, manipulative field experiments and greenhouse studies. This allows me to address hypotheses at multiple scales, from species and traits to the community- and landscape-level.
Research Interests
California's native coastal sage scrub has been heavily invaded by nonnative, invasive annual grasses, such as the Bromus rubens shown here in the foreground. In the Santa Monica Mountains (pictured here) I've found these annual grasses displace native wildflowers and reduce the establishment of native shrub seedlings.
Broadly, I'm interested in how plants respond to novel stressors and disturbances. A major focus of mine is invasion ecology -- studying the mechanisms and impacts of nonnative plant invasion. Why do some introduced species become invasive? What environmental conditions increase ecosystem invasibility? How will global change influence future invasions? How do invasive species differ from the native species they displace, or other nonnatives that don't become invasive? These are just some of the questions I hope to answer. I currently focus on the invasion of two ecosystem types in California, coastal sage scrub and native perennial grasslands. By studying how these nonnative species are able to invade and persist, I hope to inform the management of these species and aid in the prediction of future plant invasions.
While parks like Runyon Canyon (pictured here) protect native habitat in urban Los Angeles, sites closest to the city are often subject to high levels of atmospheric nitrogen deposition.
My research also explores other aspects of global environmental change in addition to plant invsions, including atmospheric nitrogen deposition. Human-caused air pollution contains significant amounts of reactive nitrogen, which is eventually deposited to the earth's surface. This excess nitrogen essentially fertilizes ecosystems and can have profound negative effects on plant community structure and function. I explore how nitrogen deposition resulting from urban Los Angeles influences native plant diversity, invasion of nonnative species, and post-fire recovery of coastal sage scrub in the Santa Monica Mountains of southern California. I'm also interested in how increased nitrogen pollution due will influence native plant communities in conjunction with predicted climate change and associated extreme drought events.