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Where Poison Oak Thrives, Mount Diablo Concludes A Red October

by on October 30, 2014

Poison oak blankets the hillsides of Mount Diablo, where it's currently the most colorful plant. (Photo by Joan Hamilton)

The ever unpopular poison oak is the most colorful plant on Mount Diablo this month, especially in certain places swept clean by the 2013 fire. On dozer paths and blackened hillsides, big crimson patches of the eerily named Toxicodendron diversilobum are roaring back to life.

Certainly poison oak knows how to handle catastrophe. The fire wiped out its above-ground stems and leaves, but most of its underground stems, or rhizomes, survived. Groups of cells in this underground tissue are perpetually embryonic, like our stem cells, enabling the shrub not only to sprout from its main stem, but also to spread out horizontally several feet from a single plant and pop up in multiple places. That gives poison oak an advantage over mere stump sprouters—and puts it way ahead of plants that can only reproduce from seeds. Germinating and growing from seeds takes rain, which has been in short supply lately.

Over time, though, poison oak’s associates will likely catch up. “As other species rebound from the fire, poison oak may cease to be so dominant,” says botanist Anna Larsen, who is studying the effects of the fire.  “That said, keep your Tecnu on hand, because it’s certainly not going away.”


This article is part of a monthly series of photos and articles on the transformation of Mount Diablo following the 2013 Morgan Fire, funded by special donations from Bay Nature readers. You can find our stories, as well as event listings, iNaturalist sightings, and magazine features, at baynature.org/diablo.


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one comment:

Merci Martin on November 6th, 2014 at 6:37 pm

The pics of the acorn woodpecker this month were fabulous.
Their antics around our valley oaks keep me laughing. Your
insight and information about the poor crop of acorns was spot
on! Our valley oak did well this year.

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