The beautiful sea of mustard flower is an invasive species in California from Europe. Like all California invaders, it is able to out-compete the native vegetation because it sprouts early and goes to seed early, then dies, while California native establishes deep root systems to survive. Noxious mustard flower plant alone is responsible 100s of native California wildflower species extinctions, along with the unique butterflies and small bees that depended on them.
It also took away habitat for the unique native California "hopping rodents" like the Kangaroo Rat.
HOW IN THE HECK DID THE INVASIVE PLANTS TURN OUT TO BE SO DIFFERENT?
California is in a weather zone that is hot and dry in summer, cool and wet in winter. There are only 5 such weather zones in the world, all located far apart from one another -- islands. Plant and animal communities formed in isolation on each island. If plants or animals from another hot dry summer/cool wet winter island got onto our island, just like with real islands, the results can be disastrous.
California's native grasses adapted for the long hot summer by growing deep roots and spacing themselves apart so as to have enough ground water to sustain them. The ground in between clumps left room for kangaroo rats to hop and a riot of colorful wildflowers to pop up every spring. Southern Europe's native grasses and annuals were adapted to the same exact climate using another strategy, by growing quickly and profusely in the winter rains, then rapidly going to seed and dying, leaving behind a large amount of seeds and a thick sea of dead, brown vegetation. The familiar brown California grasses we see today - are all Spanish. When seeds from the southern European hot dry summer, cold wet winter climate zone inadvertently arrived with the European settlers in California from Spain, their quick-to-sprout adaptation naturally took over, and quickly.
California native grass and flower communities remain in scattered patches tiny and large everywhere in California, many quietly thriving without notice because few know what these plants really look like. The reason they persist is they are a few remaining disease resistant tough curmudgeons thriving where for some reason invasives fail to move in.
WHY GO NATIVE ?
The invasive grasses weed seeds hurt pets, getting into their eyelids and fur, and snarl into human's shoes, socks. California grasses are soft, gentile and delicate.
The invasive grasses are weedy - always quickly reestablishing, and then they die and become a fire hazard. California natives stay green all year long, naturally are fire retardant, yet need no water - they have long roots that find water below.
The natives are far more beautiful - "A riot of color in the springtime."
The invasives burn frequently, the natives very infrequently, at far cooler temperatures. Protect hour house!
HERE'S THE LATEST KNOW-HOW
To get rid of aggressive weedy invasive grasses and flowers, let them sprout, then plow the ground immediately after, then repeat 5 more times over the winter, for 2-3 winters. Eventually the "seed bank" in the soil will get exhausted. Also, do a deep plow using metal rods to bore down and break up the hardpan below if the area used to be farmed. Hardpan is a layer of mineral deposits left behind by irrigation agriculture. The California natives rely on deep root systems to get to the water table - there can be no hardpan.
STUDY WHICH SEEDS YOUR PLOT OF LAND SHOULD HAVE
The invasion happened so long ago, nobody really can be sure what used to grow on any one given acre of land. The remnant patches offer the best guess.