It seems unintuitive to think that drought might be a good thing for deserts; at least for many of the native plant species that call the Anza-Borrego desert home. The recent drought that has been devastating the southwestern US has surprisingly offered a sigh of relief for some of the citizen scientists of Borrego Springs, California. You can call them the mustard hunters (that is at least how I like to think of them). More officially, they are the Sahara Mustard Weed Eradication Task Force. This group of citizen scientists collaborates with neighboring land managers and the Anza-Borrego Desert State Park and AmeriCorps student volunteers to hunt and eradicate the notorious Sahara mustard (Brassica tournefortii). They comb the town of Borrego Springs, washes of the Anza-Borrego Desert State Park, bajadas of the Santa Rosa Mountains, and alluvial flats extending to the Salton Sea. They are a team dedicated to remove this pest.
The invasive Sahara mustard is having ever-greater impacts on natural ecosystems across the southwestern US. Diversity is declining, native species are being displaced, natural resources are being altered, and conservation efforts are stalling. Sahara mustard has invaded almost every corner of the desert southwest: California, Nevada, Arizona, New Mexico, Texas, and down into the Baja peninsula and Sonoran desert of Mexico. It is common along roadsides and grows as a winter annual, sometimes choking out native winter annuals that are finely tuned to the environmental triggers required for them to germinate. Sahara mustard germinates slightly earlier than the natives and casts a harmful shadow above the natives, starving them of the resources they need for growth. Sahara mustard is a ferocious competitor when compared with the natives. A single plant produces thousands of seeds each year before breaking free from the soil and blowing down Interstate 5 as a tumbleweed. Then it is a matter of time before the traveling wreck of invasive seed pods hits a highway divider or collides with a vehicle, resulting in an explosion of seeds raining down thousands of soon-to-be Sahara mustard plants. Before they take root, the Sahara mustard seeds sit in waiting for the next fall or winter rains to queue them into action; choking the desert and its native species once again. But the people of Borrego Springs have a savior. The mustard hunters have you covered! They frequently monitor precipitation patterns, mustard sightings, and hold meetings to prepare and arm their task force of volunteers for those instigating rains that, oddly enough, make it difficult for desert natives to thrive.
Sahara mustard needs water to thrive. The winter rains that fall upon southern California bring with it cool, cloudy days. This appears to be the perfect cocktail for Sahara mustard to germinate and flourish. You might find new germinants growing under a prickly pear or brickellbush. Perhaps they are taking advantage of the shade or water provided by the natives growing above them. Either way, with the scarcity of research done on Sahara mustard, we can confidently say that it is a nuisance. The drought California has been experiencing appears have set Sahara mustard back in its invasion in at least some areas of the desert and likely only for a while. Perhaps this is only a relief for some natives since runoff and irrigation promote Sahara mustard growth in other areas. Although this may have provided a bit of relief for the mustard hunters of Borrego Springs by holding the Sahara mustard at bay, the hunters are still armed and ready with their thick, leather gloves (Sahara mustard is quite pokey!) and trowels to dig out Sahara mustard’s thick taproots, patiently waiting for the next rains to fall on the desert.