Invasive Species

I remember the moment when I first heard the term "Invasive Species".  I was at an Arbor Day event and went to a flower booth asking about a beautiful yellow flower that smelled like vanilla along Kanan Rd. I told the person behind the table that I was looking for seeds because I wanted to plant it all over my backyard.  There was shock on her face as she said the words, "Please don't plant that.  That's an invasive species." 

I later learned that the plant I "loved" was Spanish Broom (pictured above).  It is one of the Santa Monica Mountains "Evil 25".  It takes nutrients out of the soil that our native plants depend on.  It reproduces rapidly and is indigestible for our native creatures so it grows uncontrollably. 

It is not our opinion of the plant that gives it the classification of "invasive".  This classification is based on how it interacts with the other plants and ecology around it.  The problem comes when a plant or animal is introduced to a new area and it begins to destroy the other plants and animals living in that area.  

This week's newsletter is going to look closely at what an "invasive" plant or animal is, as well as highlight three species that are abundant in the Conejo Valley.
What Are Invasive Species?

Non-native species (also known as exotic species or alien species) are plants or animals that have been introduced or moved by human activities to an area where they do not naturally occur. A non-native species is not necessarily harmful, and in fact, some non-native species are beneficial (e.g., apple trees). However, when a non-native species overruns or outcompetes native species in natural communities or ecosystems and causes ecological or economic problems, it is called an invasive species.

In their new locations, invasive species do not have the natural controls that serve to limit their population in their native range. This, coupled with the fact that they typically have a high rate of reproduction and are tolerant of a large array of conditions, enables them to take over in non-native areas.

Invasive species are a world-wide problem, not just a United States one.  In fact, some of our native plant species have made their way to other continents and cause ecological problems there. The California Poppy has caused issues in Europe and lupine is quite invasive in New Zealand. 

Jessi and Squeaks from SciKids explain what invasive species are and how they effect ecosystems.
Why Should I be Concerned?
Invasive species can affect your ability to enjoy the trails and natural open space. They threaten our native ecosystems by taking away resources our native plants and animals need to survive.  If we do not attempt to control invasive species, we may lose precious wildlife species living in our open space.

It is said that the early Franciscan padres scattered mustard seeds along El Camino Real making a golden trail between the missions of Alta California that would guide weary travelers to shelter. It is not known whether this often-repeated story is true, but it makes a lovely image – in spite of the disastrous ecological consequences.

Origin: Spain. Flourishes in Mediterranean climates.

Height: Up to 12 feet.

Reproduction: Seeds scattered by winds and animals.

Range: Prevalent on dry slopes in the eastern half of the Santa Monicas but also found as far west as Ventura County.

Problem: Mustard grows profusely and produces chemicals that prevent native plants from reproducing. The spread of black mustard can increase the frequency of fires in chaparral and coastal sage scrub, changing these habitats to annual grassland.  Although some mice and small rodents find refuge under these bushes, the seeds are much too small to eat and they need to find food elsewhere. 


Crawdads are a species of freshwater crustacean that are native to the southern U.S. They are, however, invasive in California and other parts of the U.S. It is suspected that they were transported and released by anglers who were using them as bait.

Origin: South Eastern United States and Northern Mexico

Size: They can reach up to 5 inches long

Range: Any fresh water creek in the area.

Problem: Crawdads eat anything from plant debris to larvae, tadpoles, and snails. They burrow, which causes problems with water quality and creek bed erosion.  They feed on tadpoles, reducing the frog population which, in turn, increases the insect population (ie: mosquitoes).   

Sweet Fennel

Sweet Fennel has been cultivated for centuries in the Mediterranean for cooking and medicinal properties. In the mid-1800s it became more and more abundant in the United States.  If you walk along the Rancho Potrero Trail in the late summer, you will see its bright yellow flowers in the west and smell its licorice scent in the air.  

Origin: Fennel is native to southern Europe and the Mediterranean region.

Height: Up to 8 feet.

Reproduction: It reproduces both from the root crown and by seed, which are widely distributed by birds and animals.

Range:  It has naturalized widely below 2000 feet throughout the western United States and Northern Mexico; it occurs sporadically in the rest of the United States.  

Problem: It is unpalatable to most of our large grazers, protecting the mature foliage and allowing it to multiply without hesitation. The leaves exude substances that may inhibit germination of other plants.

How Can I Help


  1. Plant native plants on your property (shrink your water bill)
  2. Plant non-natives that are not on the "Evil List"
  3. Prevent seed hitch hikers
    1. Have one pair of shoes just for gardening and use a different pair of shoes for outdoor recreation activities in wild-land areas
    2. Stay on trails – helps prevents spread of seeds to new areas
    3. Keep dogs on leash and on trails- they spread seeds too
    4. Clean shoes and bicycles before and after each recreational outing

Other ways to participate:

For Educators:

If you are interested in a Project Learning Tree 50 minute lesson with activities for grades 3-8, please email Christina at and I will send it to you.  The lesson provides worksheets and activities that teach what invasive species are, why they are problematic, and how to prevent their spread. 

Conejo Open Space Non-Native Plant Resource

COSCA staff has created a guide that helps volunteers and visitors in the identification of invasive species in our area. The guide illustrates several of the more common invasive non-native plants that occur in Conejo open space areas. It also includes a few that occur in the vicinity of Conejo open space, which may become problematic in the future.

The species selected for inclusion in this guide are listed by the State of California as noxious weeds, have been recognized by the California Invasive Plant Council and/or the Santa Monica Mountains National Recreation Area, and/or are locally invasive. Some are already well- established, while others are less so.

In selecting appropriate treatment methods as part of an integrated weed management (IWM) strategy, COSCA takes into consideration the plant’s reproductive strategy, its life stage, the size and location of the infestation, and adjacent habitat and resources. Excessive soil disturbance during removal efforts is avoided. Additional information will be available in COSCA’s forthcoming non-native plant management plan. This guide is a dynamic document and will be updated periodically. It is available electronically at: or click on the picture below.

CA Native Plant Week
April 17-25

California has more types of native plants than any other state in the U.S., a third of which are found nowhere else on Earth!

Each day of California Native Plant Week, the California Native Plant Society will unveil 360° virtual tours. From home gardens to apartments, city parks to wild-lands, these 360° tours will share the different ways Californians care for and enjoy native plants. The tours also reflect a diversity of gardeners, from urbanites to suburban homeowners, Indigenous culture keepers to high school teachers.  The tours are accessed entirely online and offer an immersive experience with clickable interpretation, plant identification tags, navigation features and hyperlinked plant lists.

For more information about California Native Plant Week and the California Native Plant Society visit:

Storybook Reading
Join Antonio Sanchez as he breaks it down during his reading of "Badger's Perfect Garden" during Reading with a Ranger. Antonio knows his stuff! He works for the Santa Monica Mountains Fund and has over 15 years of experience growing native plants in nurseries and landscapes. You won’t want to miss this reading!
To read earlier issues of the Conejo Valley Nature Club Newsletter visit:
If you would like this information in a format you can distribute to your class, let's chat! Email Christina at
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