Prescribed burns fuel spread of invasive weed stinknet, jeopardizing ecosystem health

New research has revealed a concerning consequence of prescribed burns, which are commonly used to reduce the threat of wildfires and enhance habitat for certain animals. These controlled fires inadvertently contribute to the spread of stinknet, an appropriately named invasive weed that is currently invading the superblooms of the Southwestern United States.

Stinknet, also known as globe chamomile, is originally from South Africa but has become a prominent feature in photographs capturing California’s vibrant superblooms. Despite its visually appealing appearance, stinknet does not contribute to a healthy ecosystem, as emphasized by Loralee Larios, co-author of the study and an assistant professor of botany at UC Riverside.

Apart from emitting an unpleasant odor, each of the tiny yellow ball-shaped flowers of stinknet produces numerous seeds. As it continues to proliferate throughout parks, it outcompetes native plants that endangered local animals rely on for sustenance. Additionally, the invader negatively impacts soil health. In certain instances, when an invasive plant significantly alters the landscape, the soil can release stored carbon into the atmosphere, thus exacerbating the adverse effects of climate change.

To shed light on the mechanisms driving the spread of stinknet, the researchers investigated its behavior following prescribed burns. They discovered that despite large areas being scorched, numerous patches of unburned stinknet persisted in the otherwise barren ground, devoid of competition from other plants. Surprisingly, these remaining stinknet patches became focal points for further invasions, intensifying the weed’s proliferation.

This notable finding has been documented in the journal Restoration Ecology. The researchers conducted their observations in Southern California’s Lake Perris State Park, examining plant behavior on a burned plot of land over a two-year period starting in 2020. They observed that the unburned stinknet patches harbored twice the number of viable seeds compared to areas that were completely burned, lacking any residual stinknet.

It appears that singed patches create favorable microclimates for stinknet by providing optimal soil temperature, light, and moisture conditions, facilitating its continued spread.

While prescribed burns offer numerous benefits for the landscape, such as the removal of highly flammable invasive grasses, the researchers are not proposing an end to this practice. Instead, they advocate for more targeted secondary treatments to address the issue of stinknet following burns.

Possible options include manually removing patches of remaining stinknet from the ground or utilizing a technique known as solarization, which involves placing a dark tarp over an area to heat and kill any lingering seeds beneath. In more extreme cases, herbicides may be used as a last resort.

Looking ahead, the research team intends to conduct similar studies to explore how fire impacts the spread of other invasive species.

In the interim, hikers and nature enthusiasts can play a crucial role in preventing the spread of stinknet. Schwab advises cleaning boots after hikes, as they serve as a major vector for seed dispersal. Given the minuscule size of stinknet seeds (less than a millimeter wide), which are easily overlooked, simply brushing shoes periodically can significantly reduce their dispersal distance.

Furthermore, the researchers want to empower non-scientists in the effort to minimize the impact of plants like stinknet on local ecosystems. Larios highlights the importance of sharing observations with others through platforms like iNaturalist, emphasizing that many invasive plants were originally identified by non-scientists. By actively participating in data collection, non-scientists can make invaluable contributions since researchers cannot cover vast areas single-handedly.

Source: University of California - Riverside