Naturalist Segment: Poison Oak
March 29, 2019
Did you know that MBOSC has a Science Committee? It's true! We have a team of people who help bring a scientific approach and understanding to the work that MBOSC is doing. The Science Committee is full of fun facts, so we invited them to share their knowledge in a new "Naturalist Segments" series that will be appearing here in our news section. This first segment is on that infamous plant with leaves of three, written by Anderson Shepard. Itchy, itchy, scratchy, scratchy!
Words by Anderson Shepard You may start itching simply at the mention of it, or you may regard it as one of the most colorful and iconic plants growing in the redwood understory. Whatever the case may be, it is hard visit any trail in Coastal California and not have some degree of respect for poison oak.
Photo by: Patrick Tehan/Bay Area News Group
Poison oak’s scientific name is Toxicodendron diversilobum. It is in the Sumac family (Anacardiaceae) along with its close cousins Poison Ivy (T. radicans) and Poison Sumac (T. vernix), as well as other commonly known relatives such as the cashew, mango, and pistachio. The reason we have the “leaves of three, let it be” moniker is due to an oily compound that the plant produces called “urushiol” (oo-roo-shee-awl). Sensitivity among people to urushiol varies (some don't react at all, as proven in the photo below!), but in some cases exposure to even a molecular trace is enough to cause an allergic reaction. One study suggested that the amount of urushiol on the head of a pin is enough to cause rashes in 500 people. In fact, sensitivity to poison oak is so ubiquitous and can be so severe that poison oak "injuries" are covered by Workers' Compensation Insurance in California.
While scary and itchy it may be, Poison Oak also serves a number of important ecological roles. It is found from Baja to BC and is the most widespread shrub in California, growing at elevations less than 5000 ft. on all aspects west of the Sierra Nevada. It occurs in mixed evergreen forests, woodlands, chaparral, coastal sage scrub, and riparian zones. It is versatile and can grow as a single stem in grasslands, as a six foot bush, and even as a vine climbing trees high into the overstory. As such, poison oak is important habitat for numerous species of insects, amphibians and reptiles, small mammals, and birds including the federally endangered least Bell's vireo in S. California. Poison oak leaves and stems are among the most important forage for blacktail deer throughout much of the state, and the berries are consumed by many species of birds, including the California Towhee with which poison oak has developed a symbiosis. Furthermore, poison oak berries tend to persist on the plant late into the fall and can be an important food source for birds during otherwise lean times.
Photo by: Bruce Dorman
An easily-overlooked ecological service that poison oak provides is that it can out-compete many invasive, non-native species including bull thistle and giant reed, helping to limit their spread and dominance over California’s native flora.
So, next time you’re enjoying the trails, perhaps performing an elaborate singletrack ballet as I commonly do in order to “avoid all things green,” try to keep in mind some of these better qualities of our three-leaved “frenemy” and if nothing else, enjoy from afar the beauty of the brilliant (and shiny) reds and greens decorating the forest beneath the trees.
Anderson Shepard hails from Crested Butte, Colorado and is a lifelong aficionado of jagged peaks, wild rivers, deep forests, sandstone canyons, and all their constituent parts. His love of the outdoors led him to a natural science career with escapades including mapping owls, tracking wolves, collaring bighorn sheep, and lots and lots of counting flowers and leaves. Pursuit of a masters degree in GIS and conservation planning—along with the desire to ride bicycles year-round—eventually led him to put down roots in the Golden State. As a member of MBOSC and the Science Committee, Anderson works to help guide the growth of the community of trail-users in a way that respects the needs of various user groups, and preserves the integrity of the bugs and bunnies and dirt that make up our wild places and natural spaces.
Words by Anderson Shepard You may start itching simply at the mention of it, or you may regard it as one of the most colorful and iconic plants growing in the redwood understory. Whatever the case may be, it is hard visit any trail in Coastal California and not have some degree of respect for poison oak.
Photo by: Patrick Tehan/Bay Area News Group
Poison oak’s scientific name is Toxicodendron diversilobum. It is in the Sumac family (Anacardiaceae) along with its close cousins Poison Ivy (T. radicans) and Poison Sumac (T. vernix), as well as other commonly known relatives such as the cashew, mango, and pistachio. The reason we have the “leaves of three, let it be” moniker is due to an oily compound that the plant produces called “urushiol” (oo-roo-shee-awl). Sensitivity among people to urushiol varies (some don't react at all, as proven in the photo below!), but in some cases exposure to even a molecular trace is enough to cause an allergic reaction. One study suggested that the amount of urushiol on the head of a pin is enough to cause rashes in 500 people. In fact, sensitivity to poison oak is so ubiquitous and can be so severe that poison oak "injuries" are covered by Workers' Compensation Insurance in California.
While scary and itchy it may be, Poison Oak also serves a number of important ecological roles. It is found from Baja to BC and is the most widespread shrub in California, growing at elevations less than 5000 ft. on all aspects west of the Sierra Nevada. It occurs in mixed evergreen forests, woodlands, chaparral, coastal sage scrub, and riparian zones. It is versatile and can grow as a single stem in grasslands, as a six foot bush, and even as a vine climbing trees high into the overstory. As such, poison oak is important habitat for numerous species of insects, amphibians and reptiles, small mammals, and birds including the federally endangered least Bell's vireo in S. California. Poison oak leaves and stems are among the most important forage for blacktail deer throughout much of the state, and the berries are consumed by many species of birds, including the California Towhee with which poison oak has developed a symbiosis. Furthermore, poison oak berries tend to persist on the plant late into the fall and can be an important food source for birds during otherwise lean times.
Photo by: Bruce Dorman
An easily-overlooked ecological service that poison oak provides is that it can out-compete many invasive, non-native species including bull thistle and giant reed, helping to limit their spread and dominance over California’s native flora.
So, next time you’re enjoying the trails, perhaps performing an elaborate singletrack ballet as I commonly do in order to “avoid all things green,” try to keep in mind some of these better qualities of our three-leaved “frenemy” and if nothing else, enjoy from afar the beauty of the brilliant (and shiny) reds and greens decorating the forest beneath the trees.
Anderson Shepard hails from Crested Butte, Colorado and is a lifelong aficionado of jagged peaks, wild rivers, deep forests, sandstone canyons, and all their constituent parts. His love of the outdoors led him to a natural science career with escapades including mapping owls, tracking wolves, collaring bighorn sheep, and lots and lots of counting flowers and leaves. Pursuit of a masters degree in GIS and conservation planning—along with the desire to ride bicycles year-round—eventually led him to put down roots in the Golden State. As a member of MBOSC and the Science Committee, Anderson works to help guide the growth of the community of trail-users in a way that respects the needs of various user groups, and preserves the integrity of the bugs and bunnies and dirt that make up our wild places and natural spaces.
Become a Member
Become a member of SCMTS! Join thousands of members who provide a reliable stream of support as we build and maintain sustainable trails throughout the Santa Cruz Mountains.