This spring is shaping up to be a great year for a wildflower superbloom. Superblooms are typically found in years of heavy rainfall and Southern California experienced its last superbloom in 2017. In our water limited ecosystem, it is common to associate superblooms with ample water supply. However, there can be more factors that contribute to a superbloom other than water availability. The life cycle of California native annual plants typically includes flowering in spring, pollination throughout summer, and dropping seeds in fall. The seeds that are left behind at the end of a grow season can withstand years of dormancy in the soil before they are set into germination. This seeds that remain in the topsoil are a part of what is called the seed bank. Water is only one key factor that can spur seed bank germination in California native seed. In fact, many native seeds rely on some form of additional physical or chemical stratification, to germinate. Stratification is the treatment which enables a seed to germinate and usually includes some type of degradation of the outer seed casing. Weather and fire patterns are two examples of some of the many disturbances that influence the ability of native plants to germinate in California. An ideal combination of these disturbances can yield extraordinary superblooms.
Water plays an important role in seed germination and plant growth because it is the vessel by which nutrients can pass into the seed or roots to be utilized for growth. The 2018-2019 winter has brought a series of storms that have supplied an above average level of water to our local ecosystems. This annual, small-scale increase in rainfall is a way to describe weather. This recent winter weather has brought a total of 10.27 inches of rain at the Lindberg Station as of February 17. In comparison, San Diego had received only 1.87 inches of rain at the same weather station by this date last year. Long-term, annual averages in rainfall is one way to describe climate. By February 17th long-term, annual precipitation averages from 1981 to 2010 only reached 6.42 inches. This means San Diego is experiencing well above average rainfall during this 2018-2019 winter. Many native plant seeds have tough outer seed casings that are softened when exposed to prolonged moisture like we saw this winter. Water exposure is a physical example of stratification that enables germination.
Prior to this wet winter, Los Angeles and Ventura counties and Paradise, California faced fall fire storms. Luckily, San Diego made it through 2018 without major fires. California ecosystems are shaped by disturbances like fire, and species have adapted to best fit this natural history of Southern California. Although these fire storms have proven to be extremely destructive and deadly, physical and chemical components of fire play an important role in seed germination. As the heat of the fire passes over a stand of chaparral, it can level plants to ash. Not only does this process release a pulse of readily available nutrients into the soil, it also clears the soil from previously existing shrub competition. Fire directly eliminates herbivore predation through mortality and indirectly limits future herbivory due to a lack of cover and an increased risk of predation.
Heat exposure is one example of physical seed stratification; smoke and ash exposure are types of chemical seed stratifications. The heat of fire and acidic compounds found in smoke and ash can break down tough seed barriers, allowing water and oxygen to activate seed germination. Several scientific studies have resulted in a wealth of data documenting combinations of physical and chemical seed stratification which yield successful seed germination. For example, one minute of smoke exposure to seeds stimulates 100 percent germination in annual whispering bells (Emmenanthe penduliflora) seeds but not in the seed of perennial Coulter’s matilija poppy (Romneya coulteri; Keeley and Fotheringham 1998). Seed of some species require these key combinations of physical and chemical means of stratification like the ones discussed, in addition to water, light, and temperature.
Though fire can play an important role in superblooms, it can also leave barren soils exposed to the threat of major disturbances like erosion and the establishment of invasive species. Hiking boots and camping equipment can be the perfect vehicle for seeds (native or not) to hitch-hike between your favorite destinations. Cleaning the dirt and pesky grass seed from your gear before your next adventure is a great way to limit your impact and minimize the spread weedy seeds to a superbloom site.
For other tips to planning your 2019 superbloom adventure check out the following websites:
- Antelope Valley California Poppy Reserve: http://www.parks.ca.gov/?page_id=627
- Deserts: https://www.desertusa.com/wildflo/wildupdates.html
Check out these readings for more seed germination information:
https://books.google.com/books?id=CYO-AQAAQBAJ&lpg=PA673&ots=3wXjbEprKk&dq=keeley%201985&pg=PA154#v=onepage&q&f=false
Baskin, C. C., & Baskin, J. M. (2014). Seeds: Ecology, biogeography, and evolution of dormancy and germination. Amsterdam: Acad. Press.
Emery, D. E. (1988). Seed propagation of native California plants. Santa Barbara, CA: Santa Barbara Botanic Garden.
Keeley, J.E. & Fotheringham, C.J. (1998). Smoke-Induced Seed Germination in California Chaparral. Ecology. 79. 2320-2336.
Photo Credit: By Joanna Gilkeson/USFWS https://www.fws.gov/cno/newsroom/highlights/2017/desert_bloom/
