The battle against invasive French broom | Home and garden


Sci-fi movies with aliens invading and rapidly reproducing, even after a fire seems to have wiped them out, may seem like an all-too-obvious scenario to ordinary fans of the genre.

However, when you compare this plot to the life cycle of the French broom, the life of this plant mimics art, providing the Land Trust of Napa County with an ongoing stewardship battle over their protected lands.

The French broom is a non-native plant species that was introduced from Europe in the mid-1800s for local gardens and then spread to Napa County. It is the most widespread of the four non-native invasive broom species found in North America, including Scotch broom (Cytisus scoparius), Portuguese broom (C. striatus), and Spanish broom (Spartium junceum).

The green stems and small yellow flowers of French Broom look quite innocent. At the time of its introduction, no one knew that it would soon escape gardens and aggressively crowd out native plants, while increasing the risk of fire. Scotch broom, which often grows in dense patches, burns easily and provides ladder fuels that can carry fire to the forest canopy layer. Because of this, it can increase both the frequency and severity of fires in overgrown areas.

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With the recent wildfires in Napa County, you might think that at least some of the French broom has been wiped out, giving native plants a better chance to move forward.

But like the obvious sci-fi movie plot, the French broom uses this to its advantage, repelling even more aggressively thanks to a newly boosted seed bank that can lie dormant for up to 30 years.

“The term I would use for French broom – and that’s just me and not an officially recognized term – is opportunistic after a fire,” said local botanist Jake Ruygt. “He takes advantage of the cleared habitat.”

A medium-sized French broom shrub can produce over 8,000 seeds per year. A large number of dormant French broom seeds in the soil seed bank can result in very high germination rates following any type of soil or vegetation disturbance, such as a forest fire. In fact, fire often stimulates the germination of Scotch Broom seeds.

Napa MLK Day Volunteers Tackle French Broom in Westwood Hills Park

With lightsabers, infinity stones, and time travel not yet possible in the Land Trust‘s fight against the French broomstick, the job ends up being as basic as it gets. Take them out. Mainly by hand. Sometimes with a weeding key. As a perennial, French broom will also regrow from the root crown unless the taproot is removed. A weed wrench can be used to remove plants and roots, ideally before seed is set.

Last year American Conservation Experience (ACE) volunteers traveled to a Land Trust reserve where they spent three days uprooting and removing a French broom in an area that arose after the 2017 fires ACE is a non-profit organization that lends a hand to groups that may need help with their conservation work and provides opportunities for young people to work outdoors, whether it’s restoring trails, study wildlife or, in this case, remove invasive plants with the Land Trust. .

“Removing invasive species is an important part of conservation work because these invasive species can upset the balance of local ecosystems,” said ACE team leader Ashley Bouchahine.

“Additionally, due to its height and woody character, the French broom poses a significant fire hazard because it grows high enough to bridge the gap between low brush and the tree canopy,” Bouchahine said.

Thanks to the hard work of several ACE teams over several years at a number of protected Land Trust properties and the dedication of many outstanding Land Trust volunteers, large areas of French broom have gone extinct.

And while it’s not a Hollywood ending, it’s a happy ending. For now.

Jorgen Gulliksen is a staff member of Land Trust of Napa County.

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