Captivated that all plants have names, a young Justin Valliere thought, “Well, I have to learn all of the plant names.” By age eight, he was already a plant ecologist conducting pumpkin seed experiments in the family garden, and at nine, his pressed plant collections were winning blue ribbons at his county’s annual 4-H fair in rural Massachusetts.

Valliere’s now an assistant professor at the University of California (UC) Davis and knows many more plant names. His applied plant ecology lab investigates how best to restore California’s unique native plant communities that are succumbing to air pollution, climate change, invasive plants, and human land use.

He also mentors young people in restoration work while promoting LGBTQ+ visibility in scientific research. As he said in a 2023 interview, “[W]e have a long way to go in making sure that students of all backgrounds feel safe to be their authentic selves in an academic setting and in a scientific setting.”

Valliere’s research findings translate directly to land management approaches in some of California’s most rapidly changing ecosystems, including the Mojave Desert, perennial grasslands, and, of immediate importance, coastal sage scrub, one of the most endangered ecosystems in the US.

Rain brings this scrub plant community alive with heady aromas, a palette of dazzling wildflowers, and shrubs leafed out in a striking array of greens. The ecosystem — existing solely in coastal California and Baja California — consists of low-growing aromatic and drought-deciduous shrubs with an understory of wildflower and cactus species. It’s home to multiple threatened or endangered plant and animal species — some found nowhere else.

However, roughly 90 percent of the ecosystem has disappeared because, as Valliere points out, it exists “where everyone wants to build their houses along the coast, from Baja up to the Bay.” The remaining patches lie largely scattered within or adjacent to cities such as Los Angeles and San Diego where they are being displaced by exotic grasses and forbs (herbaceous flowering plants), such as wild mustard that now blankets much of the California coast in yellow each spring. (Valliere coauthored a guide, “Hold the Mustard,” to help people distinguish between native and nonnative mustard species.)

A key culprit in the continued loss of coastal sage scrub is urban air pollution, especially nitrogen compounds from vehicle exhaust that deposit onto the soil. Reducing automotive emissions is an obvious approach to restoring coastal sage scrub and other sensitive ecosystems, but while California leads the nation in setting emission standards, smog remains an issue in the region.

Researchers, including Valliere, are investigating specifically how anthropogenic nitrogen is degrading this ecosystem in order to devise other mitigation approaches. Some of this research has revealed that a devastating trifecta of pollution, climate change, and increasing wildfire frequency is impacting the ecosystem.

For example, excess nitrogen and drought cooperate in killing shrubs such as California sagebrush, an ecologically and culturally-important species. “When you give them more nitrogen…they pump out a bunch of leaves, which sounds great, right?” poses Valliere. But plants release water vapor from their leaves. “If you’re putting on more leaves, then you’re losing more water, and if you’re losing more water that makes you more susceptible to drought,” he continues. Thus, during increasingly extreme droughts, the extra foliage may be an Achilles’ heel, causing shrub die-off.

This year, Valliere and his colleagues reported on another insidious way that nitrogen pollution may be chipping away at what’s left of coastal sage scrub: It suppresses the growth of wildflowers such as whispering bells, blue dicks, California poppy, miniature lupine, and many others that bloom in spectacular displays after a wildfire and then return to dormancy in the ground as seeds or corms (swollen stem bases). Though ephemeral, these fire-following wildflowers contribute significantly to coastal sage scrub biodiversity and likely participate in post-fire ecosystem recovery. Extra nitrogen, however, speeds the already rapid germination and growth of invasive grasses and forbs that then outcompete the native wildflowers, preventing their emergence.

Nitrogen deposition also changes subterranean life in coastal sage scrub, diminishing the diversity and abundance of native soil fungi important for the growth and stress tolerance of native plants. Valliere hypothesizes that this renders the native plants more susceptible to drought, with the soil community shifts also favoring the establishment of exotic grasses.

Restoring coastal sage scrub is particularly challenging due to the pervasiveness of nonnative plants and high variability in annual rainfall, Valliere says. “It’s really tricky to restore in dry years and in wet years it may be better for seedling establishment, but wet years are also weed years.” He and other researchers are now looking to native soil fungi for improving restoration outcomes in this and other struggling ecosystems.

Climate change is another consideration. “I think climate change…complicates restoration but it further necessitates it,” says Valliere, who is increasingly interested in designing restoration approaches that reduce greenhouse gasses. California’s native perennial grasslands capture more atmospheric carbon than the invasive annual grasslands do, he notes. “So restoration… can also be a strategy to get more carbon sequestered from the atmosphere.”

While thinking ahead on restoration approaches for the coming decades, Valliere’s also promoting the future of restoration ecology as a science. For one, there’s a need for more people in the field, and he notes a dearth of undergraduate programs in restoration ecology. To help fill this gap, he has developed classes at UC Davis, and previously at California State University, Dominguez Hills, that engage college students in restoration and other ecological research that addresses local real-world problems.

“I never pictured myself going into academia and being a teacher,” he says. But his educational outreach work does date back to high school, when he worked at a science museum and created interactive exhibits that engaged students in inquiry-based learning.

Since then, Valliere has recruited Girl Scout troops to reintroduce native plants in the Santa Monica Mountains; guided elementary, middle, and high school students in native grassland restoration experiments in Riverside County, and mentored an impressive number of undergraduates on research projects while a postdoctoral fellow at the University of California, Los Angeles (UCLA). He’s also participated in the Ecological Society of America’s Seeds Diversity Mentoring Program, which gives underrepresented students hands-on experience in multiple aspects of ecology.

Indeed, there are persistent obstacles to entering and progressing in the field. Valliere shares a personal example.

“I grew up quite poor,” he says, and he was the first in his family to attend college. After graduating, he had to balance the reality of student loans with his low paying fieldwork position. Noticing that most around him working similar positions came from more financially stable backgrounds opened his eyes to the economic barriers faced by people from underserved or disadvantaged communities when entering a profession in which internships and other entry level positions pay little to nothing.

Valliere highlights another common obstacle. “When I was younger and earlier in my career, I had a lot more anxiety about being out.” This was thanks to the homophobia he experienced at different points in his career path. Research confirms that LGBTQ+ scientists at universities and governmental agencies experience more harassment, professional devaluation, and other negative experiences than their peers. In response, Valliere tries to create an inclusive and safe environment in his lab that gives people space to be themselves, focus on learning, and create novel approaches to restoration.

While he’s seen positive shifts in the scientific community, he’d like them to happen more quickly.

“I do think there are a lot of good organizations that are helping to push positive change,” he says. For example, he’s part of 500 Queer Scientists, a visibility campaign for LGBTQ+ people in STEM. And while at UCLA, he was part of QTSTEM (Queer and Trans in STEM) and the Center for Diverse Leadership in Science, organizations there that promote diversity, inclusion, and equity in science.

“There’s a need and imperative to make sure that science and conservation are… more equitable and just. That will also lead to more effective restoration strategies,” he says.

Indeed, research has shown that diversity in science fosters more innovation. But it has also revealed that while students from underrepresented communities “innovate at higher rates,” their contributions are “discounted and less likely to earn them academic positions.”

Closing this innovation-recognition gap is precisely what Valliere has been doing as part of his work on California’s vulnerable ecosystems. He also emphasizes the need for research and restoration projects to serve the diverse human communities that live in and around these ecosystems.

“We want to make sure that the scientific and land management community is serving all of California, but also if we’re thinking about how we can best restore native biodiversity in the state…we need to have diverse teams…,” he says. And this, he adds, applies beyond California, given ecosystems across the world are facing multiple and new kinds of stressors.