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Native wildflowers that thrive after fire are facing new challenges

The arrival of spring in the Santa Monica Mountains, located northwest of Los Angeles, signals a vibrant bloom of native wildflowers. These floral displays are not just a feast for the eyes; they play crucial roles in supporting local ecosystems by providing sustenance for insects, enhancing soil health, and facilitating water filtration into the earth. 

Despite their resilience and ability to recover from wildfire – a phenomenon they have adapted to over millennia – recent findings indicate that these native wildflowers are facing increasing challenges.

Vehicle emissions 

In groundbreaking research led by Justin Valliere, an assistant professor at the UC Davis Department of Plant Sciences, it has been discovered that the regrowth of native wildflowers and plants, typically expected post-wildfire, is being hindered by invasive species. 

This shift is attributed to the nitrogen found in vehicle emissions, marking a significant departure from the natural rejuvenation process following fires.

Increasing vulnerability 

“Many native plants in fire-prone areas rely on fire, and some are entirely dependent on it. Some are even most abundant after a fire. But we found that these fire-following species may be especially vulnerable to the combination of nitrogen pollution and invasive plants,” Valliere explained. This vulnerability is contributing to a noticeable decline in the native plant population within these mountains.

Fighting for resources 

The ecological dynamic described by Valliere can be likened to a depleting bank account, where the “deposits” – in the form of seeds ready to sprout following fires – are not being adequately replenished. 

While fire serves as a vital ecological catalyst, recycling nutrients back into the soil for the dormant seeds to utilize upon the next rainfall, invasive species, benefiting from an early start, rapid growth, and higher seed production, are outcompeting the natives. 

These invaders exploit the nitrogen and other nutrients from vehicle emissions, effectively winning the essential resources of water and sunlight and inhibiting the growth and maturation of native plants.

Focus of the study

The 2013 Springs Fire offered Valliere and his team, including colleagues from UC Riverside and the National Park Service, a unique window to study the effects of wildfire coupled with nitrogen enrichment on native vegetation. 

By simulating the nitrogen levels typical of Los Angeles smog in the Santa Monica Mountains test plots, the research demonstrated an accelerated decline of native plants in nitrogen-enhanced soils, post-wildfire.

Key insights

The study’s findings underscore the precarious balance native plants maintain and the dire consequences of their decline, including the potential loss of native pollinators and increased risk of mudslides. 

Valliere’s research serves as a stark reminder of the broader implications of air pollution on fire-adapted ecosystems globally, raising concerns about biodiversity in regions similar to the Mediterranean basin, southern Africa, and Australia.

As Valliere warns, the intrusion of urban smog into these delicate ecosystems could spell disaster for their biodiversity, emphasizing the urgent need for strategies to mitigate these impacts and preserve the natural splendor and ecological balance of fire-prone landscapes.

The study is published in the journal Global Change Biology.

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