9 minute read
Curb Your Enthusiasm for Invasive Plants
By: Caroline Shepherd, Habitat Restoration Technician, and Neda Brehm, Restoration Technician
You might not think about where your water comes from when you turn on the tap. It is a gift from nature, yes, but more specifically it comes from a watershed. A watershed is an area where every water droplet converges into a common outlet. We can consider watersheds on small, local levels or on large, regional levels. Either way, you are in a watershed no matter where you are on land.
Santa Barbara Botanic Garden sits within the Mission Creek Watershed, which begins high in the mountains among the Coulter pines (Pinus coulteri), flows through the rugged and breathtaking Mission Creek, and finally enters the city of Santa Barbara before emptying into the Pacific Ocean. The Garden’s watershed is home to endangered species like the steelhead trout, tidewater goby, and rare plants native only to Santa Barbara, like the rare Santa Barbara honeysuckle (Lonicera subspicata var. denudata).
Healthy watersheds provide habitats for all kinds of plants and animals, and they are vital for humans too! Watersheds provide us with clean water, flood mitigation, pollinator services, soil infiltration, recreational activities, and more, as long as they are healthy and functioning properly. Here at the Garden, that’s where our work comes in. One of our goals is to protect and care for Mission Canyon, so that it can be enjoyed for generations to come and continue to provide its key services to Santa Barbara residents.
Is the Removal of Invasive Species Really Worth the Trouble?
When watersheds are disturbed, nonnative invasive species often find ways to establish in our creeks and beyond. What are nonnative invasive species, you ask? First, not all nonnative plants are invasive, but for the ones that are, you need to look out! The invasive ones are plants that have been introduced from another region — either intentionally or unintentionally — and cause damage, from reducing biological diversity to altering basic properties of the ecosystem, like fire regimes and water availability. Accident or not, these plants have escaped their original habitats, and without the natural enemies that would have kept them in check, they can run amok. In fact, they are one of the top threats to biodiversity.
Invasive plants have developed ways to spread and thrive in harsh and unfavorable conditions, which is what makes them so successful and threatening. Because they are so easy to grow, they can be very tempting for home gardeners and horticulturalists. The fact is, at least 48% of invasive plants in California found their way from our wildlands by escaping cultivation (Bell et al., 2007). For example, the popular ornamental vine periwinkle (Vinca major) has roots that break off easily in flowing creeks and grow anew further downstream. This aggressive vine often dominates woodland understory and chokes out other native plants. You can avoid planting an invasive and support greater biodiversity by planting native plants. As an alternative to periwinkle, you can plant woodland strawberry (Fragaria vesca), beach strawberry (F. chiloensis), or Douglas Iris (Iris douglasiana) as ground covers that will favor similar conditions to periwinkle but not spread and become a noxious weed.
Other invaders like purple pampas grass (Cortaderia jubata), an ornamental bunch grass prized for its female plants that bear silky hairs on their flowers, can self-pollinate and produce numerous seeds that easily disperse to new locations by wind and water. Originating from the Andes Mountains of South America, purple pampas grass is adapted to grow in many habitats and soil types but often favors areas that receive coastal fog and have moist ground, making it a perfect contender to colonize the coastline and waterways of California’s coast. Deergrass (Muhlenbergia rigens) is a great native replacement plant with its similarly large bunchgrass form that thrives in various conditions and will attract an array of birds, butterflies, and caterpillars.
There are many reasons to help curb the spread of invasive species, but one that really resonates in Southern California is the threat of wildfires. Some invasive species can increase the frequency of fires, like Mediterranean annual grasses which dry out during the warm season and are easily ignitable. The infamous invasive annual mustards (Brassica nigra and Hirschfeldia incana) are known to paint the hills with yellow flowers in the spring and dry up during late summer to fall, creating tall stands of flashy fuels. Some invasive plants even have oils in their leaves and bark that can be highly flammable when accumulated on the ground over time, like many eucalyptuses (Eucalyptus ssp.) that are planted all over California.
A Botanic Garden Committed to Native Plants
Many botanic gardens scout and introduce new species for display and present them to the horticulture trade for their ornamental value. While this can increase visitation and add aesthetic beauty to gardens, the species can escape and become invasive in local habitats. This begs the question, is it still beautiful if it’s harming the environment we depend on? For us, the answer easily is no.
Luckily, ecosystem health and natural beauty don’t have to be compromised when you garden with native plants. At the Garden, for nearly a century, we’ve exhibited the beauty of native plants and the relationships they have with people, other animals, and the planet as a whole.
This commitment doesn’t end with our Garden boundaries.
Restoring Mission Creek Watershed
While we can’t remove all invasive species to protect native plants, we are doing what we can to protect and restore our native habitat right in our watershed. Since we know invasive plants spread rapidly through water, and typically downhill, our teams mapped invasive and rare species present in and around the Mission Creek watershed over the course of a year. This mapping helps us determine which species we should prioritize for removal based on the impact, abundance, and feasibility of us doing so successfully. Our findings are published on our website if you’d like to learn more about this process and what was discovered.
Armed with this data, one plant we’ve been able to prioritize is the removal of pampas grass since it is highly invasive, has the capability to spread rapidly with its copious seeds, and is growing directly in the creek high up in the watershed. With machetes, axes, and hori hori garden knives loaded into our packs, a team of Garden horticulturalists and restoration technicians chopped down and ripped out over a dozen plants in the upper reaches of the watershed this summer, reducing the chances of the plant spreading any further.
As you might imagine, it was hard work removing all those plants! Does this leave you wondering what you can do to help? Join us and grow native plants. It may seem like your backyard is separate from our natural environment, but it is not. Everything is connected. By planting native plants you’re helping improve biodiversity so all organisms in your area are supported. We all have the power to help our environment and ensure our local watersheds remain havens of life for everyone to enjoy.
Getting involved is easy. Here are a few ways you can start improving biodiversity today!
Use a boot brush before and after hiking to remove any invasive seeds you may be carrying on your shoes.
Avoid planting invasive plants in your home gardens. Instead, start a wildlife habitat by selecting native plant alternatives over popular ornamental plantings Check out our “Plant This, Not That” guide for ideas!
Aim for 30% native plants in your garden and if nonnative ornamentals are a must, make sure the species you choose are not invasive.
Learn how to control and properly remove invasive plants so they don’t spread further. Check out websites like Cal-IPC.org to learn about plants in your area.
Do not dump aquaria or houseplants into the environment, especially not in lakes, streams, rivers, ponds, or other natural areas.
Be a community scientist! Help land managers track invasive species by posting your invasive plant photos to iNaturalist or CalWeedMapper apps.
Become a volunteer at the Garden and learn more about native plants and other ways we’re working to ensure biodiversity thrives. Visit SBBotanicGarden.org for more tips, tricks, and content to support your journey.
Did you know?
• The economic cost of invasive plants in natural areas, agriculture, and gardens is estimated at $35 billion per year (Pimentel et al.,1999, as cited in Reichard & White, 2001).
• The global cost of invasive species is estimated at nearly 5% of the world’s economy (Thorn, 2016).
• At least 57% of endangered species are negatively impacted by nonnative invasive species (Reichard & White, 2001).
Bell, C. E., DiTomaso, J. M., & Wilen, C. A. (2007). Invasive Plants: Integrated Pest Management for Home Gardeners and Landscape Professionals. UC ANR Pub 74139. Cortaderia jubata - Bugwoodwiki. (2014, January 8). Bugwood Wiki. Retrieved October 9, 2023, from https://wiki.bugwood.org/Cortaderia_jubata Reichard, S. H., & White, P. (2001, February 1). Horticulture as a Pathway of Invasive Plant Introductions in the United States: Most invasive plants have been introduced for horticultural use by nurseries, botanical gardens, and individuals. Oxford Academic. Retrieved October 9, 2023, from https://doi.org/10.1641/0006-3568(2001)051[0103:HAAPOI]2.0.CO;2 RBG, Kew. (2016). State of the World's Plants 2016. Royal Botanic Gardens, Kew. https://www.researchgate.net/publication/320673453_State_of_the_World's_Plants_2016/citation/download
