Battling Invasive Plants at Gregerson

July 27, 2010 at 1:51 pm · Filed under Agriculture, Coast, French broom, Genista monspessulana, Invasive plants, Land Stewardship, Montara Mountain blue bush lupine

By Meghan Scanlon, Conservation Project Manager

In 2008, POST documented a dense 41-acre French broom (Genista monspessulana) infestation on Gregerson, a 203-acre property above the coastside community of El Granada that POST acquired in November 2007.

Gregerson was historically grazed, but by the mid-1980s the then-fallow fields had been infested by a “broom forest.”  The previous owners disced and planted it with oats for several years, but stopped doing so in late 2004.  Since that time, broom reemerged and migrated into surrounding scrub habitat.  The below map identifies the boundaries of the broom population as of April 2008.

Map of initial work.

The broom was encroaching on a population of endemic Montara Mountain blue bush lupine (Lupinus eximus).  POST knew that if left untreated, French broom would likely come to dominate the entire area, forming a monoculture that would make it all but impossible for the Montara Mountain blue bush lupine and other native species to survive.

POST took immediate action, treating 35 acres of infestation before plants went to seed in March 2008.  In 2009, POST worked to complete initial treatment of the entire infestation, and to re-treat the areas treated in 2008.

Hard at work.

With continued treatments in March 2009 and April 2010, POST effectively eliminated all mature French broom on the property, as well as new sprouts that had emerged after the initial 2008 treatment.  The following map identifies the areas that contained broom seedlings as of June 2010.  Note how the population has been substantially reduced!

Progress!

Ongoing follow-up treatment, which entails primarily spraying or pulling new seedlings by our dedicated volunteers, will be required for several years, due to this plant’s persistent seedbank.

Thanks to this effective treatment and scheduled follow-up monitoring and treatment, the Montara Mountain blue bush lupine, other Montara Mountain endemics, and other native plants will be able to thrive in this unique natural community.

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