Invasive Saharan Mustard Threatens Biodiversity in Southern California Deserts.

Southern California’s deserts, once believed to be naturally shielded from invasive plant species, are now facing a serious ecological threat from Saharan mustard—a fast-spreading weed that is outcompeting native wildflowers and altering the landscape's ecological balance.

A comprehensive 17-year study conducted by scientists from the University of California, Riverside (UCR), recently published in the journal Ecology, has unveiled the extent of disruption caused by this invasive plant. Led by ecologist Loralee Larios and her team, the research analyzed plant community dynamics in and around the university’s Palm Desert campus. Their findings suggest that Saharan mustard is not only displacing native species but is also compromising the desert’s natural mechanisms for weathering environmental stress.

At the heart of the desert’s survival strategy is the seed bank—a layer of dormant seeds residing within the top five centimeters of soil. This seed reserve enables native plants to wait for ideal growing conditions, particularly after long periods of drought. "It is like a literal bank account for a rainy day. When conditions are right, these seeds sprout," explained Clarissa Rodriguez, the study’s lead author and a current Natural Reserve System manager at UC San Diego.

However, Saharan mustard severely disrupts this system. With each plant capable of producing up to 15,000 seeds, it overwhelms the soil’s seed bank, drastically reducing the germination success of native plants in subsequent years. Although the study did not test for it directly, members of the mustard family are also known to emit chemicals that inhibit the growth of surrounding vegetation, potentially compounding the issue.

Under normal conditions, desert plants bloom in patterns tied to rainfall, resulting in a richly varied ecosystem. Yet, where Saharan mustard dominates, this diversity diminishes. The research found that native plants not only decline in number but also exhibit more uniform growth, weakening the system’s ability to bounce back from environmental fluctuations such as droughts or heatwaves.

Beyond vegetation, the invasive plant's reach extends to wildlife. Native animals like ants, lizards, and other reptiles depend on indigenous plants for sustenance and shelter—needs that Saharan mustard fails to meet. As a result, these species are beginning to disappear from areas overtaken by the weed.

To combat the spread, researchers recommend targeted removal efforts during wetter years—before the mustard plants release their seeds. Because the plant is easily identifiable in its early stages, land managers have a crucial opportunity to prevent its proliferation.

The study underscores the value of long-term ecological monitoring. "We typically measure invasion impacts by looking at how many native and invasive plants are present at a given time," said Larios. "But deserts don’t work that way—some years, there are almost no plants, and other years, there’s an explosion of growth."

By adopting multi-year data strategies and focusing restoration efforts on key native species, the researchers believe desert biodiversity can still be safeguarded. Their open-access study provides a model for tackling similar threats in other vulnerable desert ecosystems.

Source:https://phys.org/news/2025-04-invasive-weed-threatens-southern-california.html

This is non-financial/medical advice and made using AI so could be wrong.