How to make a rare plant bloom: take one fire-dependent Mediterranean ecosystem, add wildfire, rain, and sun, then wait six months. California wildflower displays this spring are encouragingly rich in some of the areas burned last October by wildfires. In particular Mount George in Napa County, burned by the Atlas Fire, is exploding with fire-following native wildflowers amidst blackened trunks. As nature designed, the native shrubs like chamise, toyon, and manzanita, and coast live oak trees are resprouting from burned stumps. Because these woody plants no longer dominate, rare plants can colonize the open space.
One wildflower spotted this spring hasn’t been seen on Mount George for 54 years: the Fire Poppy (Papaver californicum). Seeds have been waiting in the soil for the wildfire’s smoke to break seed dormancy so they can sprout when the rains begin. This rare annual plant, which only grows after a wildfire, was found in the Foote Botanical Preserve. Some plant species, like Clarkia, show increased germination following fire but also grow without that trigger. Fire poppies are obligate fire-followers, however, and haven’t been seen on Mount George since the last big fire in 1964.
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In September of 1964, wildfires that started with the Hanley Fire on Mount St. Helena included the Mount George Fire that burned homes and the majority of the vegetation on Mount George.
Fifty-three years later, the wildfires of last October played out in a similar fashion, with the Atlas Fire burning Mount George this time. Crooked black limbs of manzanita and chamise were most of what was left of the chaparral (shrub) vegetation that once dominated the property before the fire.
Now, six months after the fire . . . you will find not only wildflowers but bright green ankle high seedling shrubs covering much of the ground, like a ragged carpet blanketing the mountain around its rocky outcroppings.
Until the late 1990s, heat from wildfire was thought responsible for germination of fire-follower seeds. But research found that for most ephemeral (annual) and some woody chaparral species, heat-shock — a brief exposure to high temperature — isn’t responsible. The magic ingredient is smoke. A combination of chemicals produced by burning organic matter releases seed dormancy.
Smoke as a germination trigger in dormant seeds happens either directly during a fire, or indirectly after the fire has passed. An inorganic gas in smoke, nitrogen dioxide, can trigger complete germination in some species, no heat needed. Also, an organic decomposition product in smoke can stimulate germination. Of the 34 chaparral species in 13 plant families initially studied, all but 5 require smoke to germinate. Annual plants in the Pea and Rock Rose families germinate due to heat-shock. But plants in the Poppy, Sunflower, Evening Primrose, Nightshade, Mustard, and six other families need smoke. (See story beginning on page 16 of this Fremontia pdf.)
In October 2017 the Atlas Fire burned all 770 acres of permanently protected land on Mount George and 50,854 adjacent acres. The plants were ready. Their seeds remain viable in the soil seed bank for decades and can wait fifty years or more for their next moment in the sun. Heat-shock and smoke have triggered germination of dormant seeds while woody plants adapted to wildfires are resprouting from their black stumps. The burned landscape looks different now, but it also looks alive. This habitat is designed to regenerate after wildfire and stimulate the rare appearance of Fire Poppies.
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See more photos of the wildflowers on Mount George at the Napa Land Trust website and in their video below.
Bucket’s open for your nature observations.