Creek Care

Invasive Plants

Plants are at the beginning of the food chain, manufacturing the leaves, roots, flowers and seeds that feed the insects and animals that feed larger animals. For example, the California pipevine with its curiously sculpted flowers grows along our creeks and is the only food plant for the black-and-red pipevine swallowtail caterpillar, that in due course becomes the handsome black and iridescent blue butterfly seen in April. Leaves that fall into the creek and decay become food for insect larvae that feed steelhead. 

Non-native plants typically do not support a wide range of insect life, and while the presence of most non-native species is inconsequential, some crowd out or otherwise prevent native species from growing or propagating themselves. English ivy, for example, shades seedlings of other species and so prevents photosynthesis; acacias contribute chemicals to the soil that hinder the growth of other plants; French broom adds nitrogen to the soil, thus changing the nutritional balance in favor of non-native grasses.  

All plants in their native lands are limited in their ability to spread by natural controls-such as insects and competition-but when they arrive in a new ecosystem, a few of them just go wild, literally and figuratively. 

Most of the invasive plants of our creeks originated in gardens as ornamentals. These are particularly troublesome:  

• Acacia 
• Bamboo 
• Periwinkle (Vinca) 
• Cape ivy 
• Cotoneaster 
• English ivy 
• French broom 
• Giant reed (Arundo) 
• Hawthorn 
• Pampas grass 
• Privet 

Others were introduced as food plants, including:  

• Blackberry 
• Fennel 
• Fig 
• Mints 
• Onion lily 
• Cherry plum 
• Harding grass 

Removing Invasive Species 

A major aspect of habitat enhancement and restoration projects is the removal of these invasive species, and eradication in a small area can take years while seeds stored in the ground postpone germination and then awaken to become a young plant. In some cases, the removal of invasive species results in the natural return of native species. Along our creeks, alder, ash, bay, oaks, sedges, horsetail, and beeplant will often return if the conditions are favorable, but in general, the stock of native plants is so diminished that active revegetation is necessary. 

Friends urges residents to participate in invasive plant eradication efforts organized by the Marin County Parks, Marin Water, and other groups, as well as by Friends of Corte Madera Creek Watershed, and to control or eradicate them on your own property. 

When choosing plants at the nursery, check if they might spread beyond your fence.