How to Spot Invasive Plants in Our Watershed

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What does “invasive” really mean?

Invasive, non-native, naturalized, weedy… We often use these interchangeably to describe plants we think of as pests or unwanted; however, these words have slightly different definitions. For example, the words “non-native” and “native” refer to the plant’s origin in reference to its current context. The words “invasive”, “noxious weed”, and “naturalized” refer to how a plant interacts with the ecosystem it inhabits. Specifically, it means that the species is likely to cause economic or environmental harm. This is where things become nuanced. A plant can be both native, thus culturally and biologically important to an ecosystem, and also invasive, reducing biodiversity and causing ecological detriment.

Let’s get to know some non-native noxious weeds in our watershed. For a plant to be categorized as a noxious weed it must be (1) harmful to ecosystems and/or native species and (2) difficult to control or eradicate. The following are examples of non-native noxious weeds present in our watershed that are looking to spread. Though some of them may look beautiful in the spring, don’t be fooled by their pretty flowers and florets. These plants can be quite harmful to our local ecosystems.

SYRCL works to remove invasive species in our watershed because doing so is a key part of mitigating wildfire risk and protecting the abundant density of rare plants native to the foothill’s serpentine soils. 

Invasives in our area

Scotch broom, like many successful weeds, has several characteristics that help it to persist in the landscape and choke out native vegetation. Not only is it not picky about what kind of soil it grows in, Scotch broom also hosts nitrogen-fixing bacteria in its roots that allow the plant to invade nutrient-poor soils.

You may be thinking, “Why should I care? I’m not a native plant. Scotch broom doesn’t affect my daily life.” It’s important to note that Scotch broom has increased the fire fuel loads in the Sierra Nevada as a result of its dense growing pattern. In other words, Scotch broom puts us all at risk in the event of a wildfire.

Deceptively lovely, Scotch broom enjoying the sun. Image: SYRCL Staff

Common name: Scotch broom
Scientific name: Cytisus scoparius
Family: Fabacea (Pea family)

Cal-IPC Rating: High (This means I’m widely distributed and have severe impacts!)

Something people don’t know about me: Because I’m so good at using water, I was employeed for erosion control along highway cuts when I first arrived in California.

Favorite way to be controlled: I can be mechanically removed (think pulling by hand or with a weed wrench), but you have to pull my whole root out, or I’ll be back!

Bloom period: May through March

Yellow star thistle can create thickets that out-compete native vegetation. Its wide distribution across rangelands, roadsides, and agricultural lands allows for further spread of the plant via cars, agricultural equipment, animal fur, and hiking boots. Although this weed is already widespread, always check your hiking boots, backpacks, and pants for seeds after a day outside to reduce local invasion.

Despite the allure of its golden petals, this yellow star thistle could infest your roadside or yard. Image: USDA ARS.

Common name: Yellow star thistle
Scientific name: Centaurea solstitialis
Family: Asteraceae (Sunflower family)

Cal-IPC Rating: High

Something people probably already know about me: I’m a pain in the ankle. Walk around me or walk over me at your own risk!

Favorite way to be controlled: Try anything: hand pulling, intensive grazing, biological control agents (insects), herbicides, prescribed burning…regardless you’ll have to treat me every year at just the right season in order to see results. 

Bloom period: April through September

Medusahead is skilled at growing in thick patches that outcompete native grasses and forbs – are you detecting a pattern yet? The long awns for which it is named allow the seeds to hitch a ride on any person or animal that brushes by, thus extending its distribution. Furthermore, this grass is unpalatable to birds and grazing animals after its early stages of growth, causing cascading impacts on plant biodiversity as well as animal biodiversity.

Me and my cousin Barbed goatgrass. I’m the one on the right. Image: SYRCL Staff

Common name: Medusahead
Scientific name: Elymus caput-medusae
Family: Poaceae (Grass family)

Cal-IPC Rating: High

Something people don’t know about me: I get my name from my long awns, or bristles, that extend from my plant glumes in a snake-like appearance.

Favorite way to be controlled: Prescribed burning works well on me, but only at lower elevations. Since cows find me unpalatable most of the year, you have to graze me early in the growing season, before I bloom.  

Bloom period: April through July

Well you guessed it; barbed goatgrass invades by creating monocultures that take over native vegetation. This weed can even invade serpentine soils, which are high in iron, chromium, nickel, and cobalt and often only support growth of endemic plants. Similar to medusahead, barbed goatgrass is highly unpalatable to grazing animals, so much so that if the barbs get imbedded into a cow’s eye, nose, or throat, it can fatally injure the cow.

I’m not here to make friends. Image: SYRCL Staff

Common name: Barbed goatgrass
Scientific name: Aegilops triuncialis
Family: Poaceae (Grass family)

Cal-IPC Rating: High

Something people don’t know about me: I’m small but tough. I’ve even been know to kill a cow!

Favorite way to be controlled: I can be controlled via hand pulling, grazing, and prescribed burning, but best is a combination that incorporates a multi-year treatment plan. Some say I’m demanding but I say I deserve it! 

Bloom period: March through July

If any of these plants caught your eye, you can do more research on the Calflora and Cal-IPC websites. These are great resources to explore photos, relative research, and interactive maps describing distribution. Be sure to look out for these plants in your backyard, on hikes, and on roadsides and think twice before admiring their beauty. 

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