California’s native wildflowers are struggling due to layers of dead, invasive grasses. A recent study from UC Riverside indicates that raking these layers can enhance biodiversity and lower fire risks.
California’s native wildflowers are struggling due to layers of dead, invasive grasses. A recent UC Riverside study indicates that raking these layers can enhance biodiversity and lower fire risks.
The study, released this week in Restoration Ecology, examined if removing thatch—composed of dead leaves and debris—would help native seeds sprout and thrive. In contrast to methods for managing invasive grasses such as controlled burning, hand weeding, or applying herbicides, raking is significantly less labor-intensive and is more environmentally friendly.
“In these ecosystems, native seeds frequently land on thick layers of thatch and can’t germinate. Raking the thatch allows light to penetrate and gives native plants a chance to flourish,” explained Marko Spasojevic, the study’s author and a UCR associate professor specializing in plant ecology.
At grasslands near the UCR campus, researchers established paired plots—one that was raked and another that was left untouched—to observe plant community changes over a three-year period. The findings revealed that raking generally increased plant diversity, diminishing invasive grasses such as ripgut brome while promoting both native and exotic wildflowers, known as forbs.
Ripgut brome, the leading invasive grass, gets its name from its sharp, bristly hairs, which can harm grazing animals. “It’s really harmful for sheep and cattle to consume,” noted Spasojevic. Conversely, native flowers such as the common fiddleneck, abundant in Riverside, showed slight improvements thanks to raking.
While raking curtailed invasive grasses, it came with a drawback: it also encouraged the growth of certain exotic wildflowers, including mustard, which can be very invasive.
“Raking increased the presence of native wildflowers by around 5%, while exotic forbs rose by 7 to 10%,” stated Advyth Ramachandran, who helped lead the project as an undergraduate at UCR and is now studying plant ecology at the University of Colorado Boulder. “This suggests that raking is still valuable. It’s a simple and cost-effective approach that could serve as an initial step towards restoring these ecosystems.”
The origins of this project date back decades. The study plots were initially set up for an introductory biology course in the 1980s but were later neglected. During the pandemic, Ramachandran and other UCR students revitalized the area, launching a grassroots research effort through the university’s SEEDS club.
“We launched this project from the ground up, developing protocols, identifying species, and involving over 25 undergraduates,” Ramachandran said. “It’s uncommon for undergraduates to start and spearhead publishable research like this.”
Spasojevic attributes the project’s success to its accessibility. “Since the research site is located on campus, students could collect samples between classes. This made it easier for them to participate and created valuable mentorship opportunities,” he remarked. The SEEDS initiative is ongoing, with students continuing their data collection for a fifth consecutive year.
The team’s results have practical implications for land managers looking for economical ways to restore native plant diversity in grasslands and coastal sage ecosystems.
Native plants support local wildlife by providing food and habitat, aiding pollinators like bees, and helping to prevent soil erosion. In contrast, invasive grasses not only outcompete native plants but also raise wildfire risks due to their dense, flammable materials. Promoting native wildflowers is essential for restoring and preserving healthy ecosystems.
“This project illustrates how simple actions—like raking—can lead to significant improvements in our ecosystems,” Ramachandran noted. “It’s an encouraging step towards revitalizing California’s native landscapes.”
