Superbloom

Superbloom in Riverside County, California in 2019

A superbloom is a rare desert botanical phenomenon in which an unusually high proportion of wildflowers whose seeds have lain dormant in desert soil germinate and blossom at roughly the same time. The phenomenon is associated with an unusually wet rainy season. The term may have developed as a label in the 1990s.^[1][2]

Necessary conditions and sequence of events[]

The conditions under which a superbloom can occur are exceptional. Because some invasive grasses, such as bromes, will compete with native flowers for moisture, the desert must remain dry enough prior to the bloom to keep them from becoming established.^[1] The desert must receive rainfall in the autumn, and this rain must penetrate deep into the soil matrix in order to reach a majority of the dormant seeds of flowering plants. If subsequent rainfall is excessive or inundating, the young plants may be carried away in flash floods; if it is inadequate, the seeds will die from dehydration.^[3]

Next, the ground in which the seeds lie must warm slowly over the several months which follow the first soaking rain, and the desert must have enough cloud cover both to shield the soil from intense daytime desert heat and to insulate it from overnight freezing temperatures. Finally, once the newly germinated plants have reached the surface of the soil, the desert must remain undisturbed by strong winds which would uproot the plants or damage the young shoots. The rare concatenation of these events is what makes a superbloom such an extraordinary occurrence.^[3]

Carrizo Plain National Monument in 2017

In California, common plants which participate in superblooms are brittlebush (yellow flowers),^[4] California poppies (bright orange),^[5] bluebells (deep purple),^[1] lupine (purple), sand verbena (yellow), desert sunflowers (bright yellow), evening primrose (mostly white, occasionally yellow), popcorn flowers (white or yellow), and desert lily (white).^[6][7] Several of these plants are also invasive, such as wild mustard.^[8]

In California, superblooms typically occur once every ten years or so. This has happened less often since the beginning of the 21st century due to persistent state drought. The state's Anza-Borrego Park is one of the most popular places to witness a superbloom, and the bloom of 2019 was particularly abundant. This followed another only two years prior, in 2017.^[9]

Tourism effects[]

Due to the massive influx of tourists, flowers were trampled. A number of people picked them or plants were pulled out with their roots.^[10] Additionally, massive traffic jams from the cars the tourists used prompted Lake Elsinore, California to shut down access to Walker Canyon.^[11][12]

Algal superblooms[]

Because algae often reproduce in large sporadic bouts, referred to as algal blooms, the term "superbloom" is sometimes applied to especially prolific short-term algal growth that causes discoloration of water on a large scale.^[13][14] Other than sharing a botanical context, however, the two events have nothing in common.

References[]