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A major reason for the continued loss of coastal sage scrub is urban air pollution, particularly nitrogen compounds from automobile exhaust that are deposited in the soil. Reducing automobile exhaust is an obvious approach to restoring coastal sage scrub and other delicate ecosystems, but throughout California, smog remains a problem in the region.

Researchers, including Valliere, are specifically studying how anthropogenic nitrogen is destroying this ecosystem to develop other mitigation approaches. Some of this research has found that a devastating trifecta of pollution, climate change and increasing wildfire frequency is affecting the ecosystem.

For example, excess nitrogen and drought are causing shrubs like California sagebrush, an ecologically and culturally important species, to die. “If you give them more nitrogen, … they put out a lot of leaves, which sounds great, right?” Valliere asks. But plants release water vapor from their leaves. “When you get more leaves, you lose more water, and when you lose more water, you’re more susceptible to drought,” he continues. So during increasingly extreme droughts, the extra foliage can be an Achilles heel, causing shrubs to die.

This year, Valliere and his colleagues reported another insidious way nitrogen pollution could be destroying what’s left of the coastal sage scrub: It suppresses the growth of wildflowers like whispering bells, blue dick, California poppy, dwarf lupine, and many others that bloom spectacularly after a wildfire and then return to the soil as seeds or tubers (swollen stem bases) and lie dormant. Although short-lived, these fire-following wildflowers contribute significantly to the biodiversity of the coastal sage scrub and are likely involved in the ecosystem’s post-fire recovery. But additional nitrogen accelerates the already rapid germination and growth of invasive grasses and herbs, which then crowd out the native wildflowers and prevent their emergence.

Nitrogen deposition also alters the underground life in coastal sage scrub, reducing the diversity and abundance of native soil fungi important for the growth and stress tolerance of native plants. Valliere suspects this makes native plants more vulnerable to drought, with the changes in the soil community also favoring the establishment of exotic grasses.

Restoring coastal sage scrub is particularly difficult because of widespread non-native plants and the wide variation in annual rainfall, Valliere says. “Dry years are really difficult to restore, and wet years may be better if seedlings become established, but wet years are also weed years.” He and other researchers are now looking for native soil fungi to improve restoration outcomes in this and other endangered ecosystems.

Climate change is another consideration. “I think climate change makes restoration more difficult, but also makes it necessary,” says Valliere, who is increasingly interested in developing restoration methods that reduce greenhouse gases. California’s native perennial grasslands sequester more atmospheric carbon than the invasive annual grasslands, he notes. “So restoration can also be a strategy to sequester more carbon from the atmosphere.”

In addition to thinking about restoration approaches for the next few decades, Valliere is also promoting the future of restoration ecology as a science. For one thing, there is a need for more people in the field, and he notes a lack of undergraduate programs in restoration ecology. To fill that gap, he has developed courses at UC Davis and previously at California State University, Dominguez Hills, that engage students in restoration and other ecological research that addresses local, real-world problems.

“I never imagined I would go into science and become a teacher,” he says, but his work in education dates back to high school, when he worked at a science museum, creating interactive exhibits that engaged students in inquiry-based learning.

Since then, Valliere has recruited Boy Scout groups to reintroduce native plants to the Santa Monica Mountains, led elementary, middle, and high school students in experiments to restore native grasslands in Riverside County, and mentored an impressive number of students on research projects as a postdoctoral fellow at the University of California, Los Angeles (UCLA). He has also participated in the Ecological Society of America’s Seeds Diversity Mentoring Program, which provides underrepresented students with hands-on experience in multiple aspects of ecology.

In fact, there are persistent obstacles that hinder entry into the field and advancement within it. Valliere gives a personal example.

“I grew up pretty poor,” he says, and he was the first in his family to go to college. After graduating, he had to juggle student loans with his low-paying job as a sales rep. When he realized that most of those around him who worked in similar positions came from more financially stable backgrounds, his eyes were opened to the economic hurdles that people from underserved or disadvantaged communities face when entering careers where internships and other entry-level positions pay little to nothing.

Valliere highlights another common obstacle. “When I was younger and early in my career, I was much more afraid to come out.” This was due to the homophobia he experienced at various points in his career. Research confirms that LGBTQ+ scientists in universities and government 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 develop novel approaches to recovery.

Although he has observed positive changes in the scientific community, he would like to see them happen more quickly.

“I believe there are a lot of good organizations out there that help drive positive change,” he says. For example, he is 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 that promote diversity, inclusion, and equity in science.

“It is necessary and imperative to ensure that science and conservation become more just and fair. This will also lead to more effective restoration strategies,” he says.

In fact, research has shown that diversity in science promotes greater innovation. But it has also shown that while students from underrepresented groups “produce more innovation,” their contributions “are ignored and leave them with fewer opportunities for academic positions.”

Bridging this gap between innovation and recognition is Valliere’s goal in his work on California’s endangered ecosystems. He also emphasizes the need for research and restoration projects that serve the diverse human communities that live in and around these ecosystems.

“We want to make sure the scientific and land management community serves all of California, but also as we think about how best to restore native biodiversity in the state, we need diverse teams,” he says. And that, he adds, is not just true for California, as ecosystems around the world are facing numerous and new types of stressors.