We have our share of invasive species here in the Bay Area. There are aquarium plants (Egeria densa) in the delta, eucalyptus trees (Eucalyptus globulus) on hills , yellow star thistle (Centaurea solstitialis) on grazing land, and the local government is desperately trying to keep zebra mussels (Dreissena polymorpha) out of the local lakes. But the worst offender in our neighborhood is French Broom (Genista monspessulana).
The bright yellow flowers are blooming everywhere around here now, and their sweet smell is enjoyed by many. If you go hiking in the open spaces and regional parks, however, you realize that it is a fast-moving wave that chokes out almost all native plants in its path. The East Bay Regional Park District has organized volunteer work parties to clear their parks of this monster. They have attracted a lot of workers, including Wendy Tokuda, a local news anchor woman during the 80's and 90's. She gets out there and pulls up weeds with the rest of the volunteers, using a 'weed wrench,' a device specifically invented to make pulling these weeds easier.
When we bought our house, the neglected backyard was thick with broom. We spent a couple of weekends pulling it up by the roots and all, but every spring we find little broom plants sprouting up everywhere. By summer's end, the seed pods from broom are plump and all it takes is a good, hot day and blammo! The pods burst open and fling their spawn everywhere. We've hiked in open spaces on such hot days, and you can actually hear the pods popping along the trail.
It looks like we will have a never-ending battle to keep them at bay. If that isn't enough, I saw these plants for sale at Home Depot in gallon containers for $4.99!!! Please Home Depot, enough is enough!
I wonder in the big scheme of things just how bad a problem an invasive species like French Broom is. We tend to look at our world and think it is static, that the world has always been as it is now or as it was when you were a kid, so every change seems extreme and permanent. But if you could watch a time lapse video of a local hillside for the last million years or so, would it show one invasive species after another getting a foothold and then taking over, only to be replaced by another 'invasive species' in its time?
They say French broom has no natural enemies, but how long will it be before something adapts to control this suddenly available food and fuel source? I saw the local cotton tail rabbits taking cover under it's dense brush in Wildcat Canyon Park. Of course, in ancient times, without humans to introduce new species to this area, invasive species were fewer in number and slower to establish, so the abruptness of these changes is the real issue.
The name 'invasive species' makes it sound like they came here by their own means with the evil purpose of taking over the land, "mwah-ha-ha-ha." But every species mentioned above was introduced here by humans, either on purpose or accidentally, and they have found this area to their liking and have flourished. As I play that imaginary time lapse video in my head, it seems that the one true invasive species is the humans, (Homo sapien).