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Bromus diandrus and Bromus tectorum
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Invasive Plants


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Invasive Plants


Invasive plants are plant species introduced to our area from other parts of the world, that out-compete native vegetation and dominate plant communities.

Conversely, native plants are generally defined to be plants found in our region before European colonization, roughly 200 years ago. Native plants have evolved together with native animals so that each species fills a specific niche and there are checks and balances to each species' populations. Native plants are generally controlled by competition with other species, herbivory from native animals, nutrient availability, and other ecological factors. A community of native plants provides a mosaic of food sources, shelters, and niches for a diversity of native animals. Essentially, a greater the diversity of native plants means a greater diversity of native animals. Invasive plants, having evolved in other plant communities, disrupt this delicate balance because they aren't controlled by competition with other plants or animals.

Invasive plants, such as black mustard, rip-gut brome, fennel, Russian thistle, Arundo, cape-ivy, and tamarisk just to name a few, are some of the most destructive invasive plants in our region (the California Invasive Plant Council keeps an near-full list of California's invasive plants).

Listed below are some of the Central Coast's most common invasive plants.

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Black Mustard


Black Mustard


Black Mustard (Brassica nigra)

Anyone heading north on the 101 through Gaviota after winter rains should be familiar with the bright yellow hillsides bordering the highway. Beautiful as it may be, it's easy to see that this plant can easily dominate large patches of land.

Black mustard (named for its black seeds, not the bright yellow flowers, of course) quickly establishes itself in disturbed areas (such as post-fire or bulldozing). Once established, these thick stands of plants growing up to six feet tall easily crowd out any other plant life.

 
 Large monocultures of black mustard are common throughout the San Marcos Foothills Preserve, crowding out native grasslands that so many of our native animals rely on,

Large monocultures of black mustard are common throughout the San Marcos Foothills Preserve, crowding out native grasslands that so many of our native animals rely on,

 

Black mustard (named for its black seeds, not the bright yellow flowers, of course) quickly establishes itself in disturbed areas (such as post-fire or bulldozing). Once established, these thick stands of plants growing up to six feet tall easily crowd out any other plant life.

 Fields of dead mustard provide a good source of fuel for wildfires (and are frankly an eyesore after their short lived flowering phase).

Fields of dead mustard provide a good source of fuel for wildfires (and are frankly an eyesore after their short lived flowering phase).

As an annual plant, black mustard quickly dries out and drops its seeds at the end of the rainy season. These huge stands of dead plant material present a much greater fuel load for wildfires as opposed to our native grasslands.

It is difficult to eradicate black mustard. Even after removing black mustard, it can easily grow back from seed deposits in the soil. However, once native plants are reestablished in an area, our plants can choke out black mustard and prevent it from growing. Channel Islands Restoration is working to eradicate black mustard in critical habitat areas by systematically removing black mustard stands and quickly planting natives in its place.

Fun fact: the flowers are edible and actually taste like spicy mustard. Maybe add them as a nice garnish to a salad?

 
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Bromus diandrus and Bromus tectorum

Ripgut Brome


Ripgut Brome


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Ripgut brome (Bromus diandrus) is a very common invasive grass that has established itself in our region's grasslands. Anyone walking through a meadow in the summer is probably familiar with this invasive plant as, following said walk, you've probably spent a few minutes picking its seeds out of your socks.

Ripgut brome is named for its spikey barbs that hook onto clothes, fur, and, as the name suggests, the stomach linings of herbivores. European livestock animals like goats, sheep, and cattle evolved with the grass so they are somewhat adapted to graze it, but our native herbivores like rabbits and deer are less equipped to graze on it. Therefore, ripgut brome can, for the most part, grow unmolested and dominate grasslands.

Ripgut brome is an annual grass, meaning it grows quickly following rain, drops its seeds, and then dries out and dies shortly thereafter. It also grows in dense patches and crowds out native grasses. This contributes to increased fire load when compared to our native grasslands.

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This invasive grass often displaces purple needlegrass - our native equivalent (and California's official state grass). In comparison, purple needlegrass has smooth (non-barbed) seeds which don't irritate herbivores' stomachs. It grows in bunches, rather than uniform mats, so it allows for open ground between plants which provide opportunities for birds like black pheobes to land and grab insects or for hawks to swoop in and grab a rodent that was foraging for seeds. Purple needlegrass is also a perennial plant, meaning it lives year-round, which means it stays green longer and stores water during the summer. As a perennial bunchgrass, it presents a significantly lower fire hazard when compared to ripgut brome dominated grasslands.

Ripgut brome is difficult to control, but can be done through maintained grazing from livestock. As an annual grass, ripgut brome cannot easily regenerate from its root after being munched by herbivores, but purple needlegrass, as a perennial plant, stores most of its nutrients in its roots and can withstand and regrow after light grazing.

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Tamarisk


Tamarisk


Tamarisk, Salt Cedar (Tamarix ramosissima)

Tamarisk (Tamarix ramosissima) is one of the most detrimental and troublesome invasive plants of the Southwestern United States. These large, deciduous shrubs were brought from the Middle East to the United States as ornamental plants, prized for their showy plumes of pink flowers, and then later used as windbreaks and hedges. Their hardiness, drought tolerance, and ability to grow in poor soils makes them a popular, low-maintenance shrub to cultivate. Unfortunately, their resilience is exactly what makes it such a troublesome invasive plant. Once established, tamarisk can spread quickly and dominate entire riparian (streamside) ecosystems with devastating consequences for plant and animal life alike.

 Adult tamarisk with a person for scale.

Adult tamarisk with a person for scale.

 Tamarisk seedlings quickly send taproots down into the soil to anchor themselves within a streambed. A seedling just a few inches tall can have a taproot that is longer than a foot.

Tamarisk seedlings quickly send taproots down into the soil to anchor themselves within a streambed. A seedling just a few inches tall can have a taproot that is longer than a foot.

Once established, tamarisk severely affects native plants in a number of ways. Tamarisk is also called salt cedar because it is able to pull salts from the soil and excrete them through their leaves. Native birds and grazing animals may avoid stands of tamarisk for this reason. When these leaves drop, they create a thick, salty mat that negatively affects soil and water quality, and impedes new native plant growth. This means new trees like cottonwoods or sycamores cannot sprout, therefore reducing available nesting habitat for birds, roosting areas for raptors, and opportunities for other animal species. Additionally, a single tamarisk tree can drop as many as 50,000 seedlings in a season, flooding a streambed with seedlings that can potentially grow to choke out streams. Tamarisk also is able to sprout from their deep root systems, meaning a single tree can grow into a dense thicket that pushes out any other plant life and individuals can quickly recover from being cut down. Thickets can sometimes grow so thick that larger animals like deer, bears, and mountain lions cannot move through them.

 
 Adult tamarisk plants have a distinctive red bark.

Adult tamarisk plants have a distinctive red bark.

 

Tamarisk also affects streams and rivers themselves. By creating thick walls on either side of a stream or river, the plants channelize the river, reducing the number of eddies and pools available for fish and amphibian spawning. By crowding out taller native plants, they expose rivers to more sunlight, warming the water and reducing its oxygen content, which can be devastating for aquatic life.