Prescribed burns encourage foul-smelling invaders

New research indicates that while prescribed burns are effective in reducing the risk of wildfires and enhancing habitats for certain animals, they also contribute to the spread of stinknet, a weed that is currently invading superblooms in the Southwestern United States. The aptly named stinknet weed poses a challenge as it proliferates alongside the benefits achieved through prescribed burns. This research sheds light on the unintended consequences associated with prescribed burns and highlights the need for careful consideration and management of these practices to mitigate the spread of invasive species like stinknet.

Stinknet, also known as globe chamomile, is originally from South Africa but has become a common sight in photographs of California’s vibrant superblooms. However, despite its visually striking appearance, stinknet does not contribute to a healthy ecosystem, according to Loralee Larios, co-author of the study and an assistant botany professor at UC Riverside. While superblooms are often associated with diverse and beneficial flowering plants, stinknet stands out as an exception due to its invasive nature and negative impact on the ecosystem. It serves as a reminder that not all flowering plants are beneficial or indicative of a thriving ecosystem.

In addition to its unpleasant odor, each of its tiny yellow ball-shaped flowers can hold hundreds of seeds. While expanding across entire parks, it crowds out native plants on which endangered local animals rely. 

In addition to its detrimental impact on the ecosystem, stinknet invasion also affects the overall health of the soil. Invasive plants like stinknet can alter the composition of the landscape, which can have serious consequences. One such consequence is the potential release of stored carbon from the soil into the atmosphere. This process can exacerbate the negative effects of climate change by contributing to increased greenhouse gas emissions. It highlights the interconnectedness between invasive species, soil health, and the global climate, emphasizing the importance of managing and controlling invasive plants to mitigate these adverse effects.

Recognizing the importance of understanding the spread of stinknet, the researchers conducted a detailed investigation into its mechanisms. They discovered that following a prescribed burn, numerous unburned patches of stinknet persist in areas that are otherwise devoid of vegetation and competition from other plants. Surprisingly, these leftover stinknet patches act as focal points for further invasions. Loralee Larios explains that rather than being eliminated by the burn, these patches actually facilitate the expansion of stinknet, leading to its continued spread. This insight highlights the complex dynamics between prescribed burns, invasive species, and the subsequent ecological consequences, underscoring the need for effective management strategies to mitigate the proliferation of stinknet.

The researchers published their findings on the spread of stinknet in the journal Restoration Ecology. To gather this information, they conducted observations on a burned plot of land located in Lake Perris State Park in Southern California. Starting in 2020 and spanning two years, the researchers closely monitored the behavior of plants in the area. Their observations revealed that the unburned patches of stinknet had twice as many viable seeds compared to the areas that were completely burned, where no residual stinknet remained. This indicates that the presence of unburned stinknet patches significantly contributes to the seed bank and subsequent proliferation of this invasive weed. The study provides valuable insights into the long-term impacts of prescribed burns on stinknet infestations and underscores the need for effective management strategies to prevent further spread.

It appears that singed patches create favorable microclimates for stinknet, creating soil temperature, light, and moisture conditions that help it spread.

In their research, the team also discovered that reintroducing native plant seeds to the burned area did not result in a significant increase in native species presence. Stuart Schwab, the lead author of the study and a doctoral candidate in plant sciences at UCR, suggests that stinknet likely releases chemicals through its roots that have a detrimental effect on soil fungi. These fungi are essential for the growth and establishment of native plants. The presence of stinknet in the ecosystem disrupts the symbiotic relationship between native plants and soil fungi, hindering the successful restoration of native species following a prescribed burn. This finding highlights the challenges involved in reestablishing native plant communities in areas invaded by stinknet and emphasizes the importance of developing effective management strategies to combat this invasive species and restore ecological balance.

Because prescribed burns offer so many benefits for the landscape, including removing highly flammable invasive grasses, the researchers are not suggesting that land managers end the practice. Rather, they are calling for more targeted, secondary stinknet treatments after burns. 

Schwab suggests several potential options for managing stinknet infestations. One approach is manual removal, where patches of remaining stinknet are pulled out of the ground by hand. Another method called solarization involves placing a dark tarp over an area to raise the temperature and effectively kill any remaining stinknet seeds underneath. These non-chemical approaches can be considered as initial strategies to control the spread of stinknet. However, if these methods prove ineffective or if the infestation is severe, herbicides may be used as a last resort. It is important to carefully evaluate and consider the potential ecological impacts and follow appropriate guidelines and regulations when using herbicides to ensure minimal harm to the surrounding environment.

Going forward, the research team would like to conduct similar studies to understand how fire impacts the spread of other invasive species. 

Meanwhile, people who enjoy hiking and nature can contribute significantly to preventing the spread of stinknet. Schwab advises, “Make sure to clean your boots after hiking because they are a major way the seeds spread. These seeds are incredibly small, less than a millimeter in width, so they can easily go unnoticed. Simply brushing your shoes regularly can greatly reduce how far they can travel.”

Finally, the researchers want non-scientists to feel empowered in the fight to minimize the impact of plants like stinknet on local ecosystems. 

Most of the invasive plants that we know about today were actually first discovered by people who are not professional scientists. In the case of stinknet, it was undergraduate students from UC Riverside who first found it. Larios emphasizes the importance of sharing such discoveries with others through platforms like iNaturalist. This is crucial because researchers alone cannot cover a large enough area to identify and monitor all invasive species. By involving the broader community, we can collectively contribute to a better understanding of invasive plants and their impact.