Invasive plants… whats the big deal?

A group of local students recently asked us some questions about invasive species in Orange County, specifically mustard. Our Horticulture Manager Michael Viramontes was kind enough to answer them, and his answers are so great that we thought we’d share them with YOU!

What makes invasive species so detrimental are their ability to take over native habitat and decrease the cover of native species. Invasive species usually have a large amount of seeds per plant and have high percentage of seed viability. Also, invasive species are effective at getting to the stage of seed production even in degraded landscapes. They can do this by taking up all the resources in the short period that they are available (i.e. California’s rainy season), producing seed, dropping it, and then dying. In addition to having all of these characteristics, since they are outside of their native habitat, their natural predators aren’t around to consume them (which would keep their population in check). Now that I have listed these characteristics, I will discuss the issues that arise from them below.

Because of their characteristics, invasive species usually grow in large patches creating what is called a monoculture. A large area of a single, or even just a couple different types of invasive plants. This give that habitat a really low level of biodiversity, and can support a smaller diversity of pollinators and predatory species. In other words, invasive plants inhibit the natural biodiversity.

Since the small invasive herbs and grasses usually have shallow root structures and die back every dry season they can create fields of dry brush and increase the chances of wildfire. Although much of California’s native habitat is ecologically adapted to need wildfires, fires in native habitat have much less “fuel” to burn. “Native fires” burn at lower temperatures and at lower shrub levels. Besides fires, the shallow root structures in invasive monocultures can leave hillsides susceptible to erosion/landslides.

It depends on how you ask the question. There is NO benefit of having invasive species, in any place you don’t want it (wild areas especially). The only benefit they could bring is whatever reason they were brought here to California in the first place. For example, invasive mustards were brought as a cover crop to add nitrogen to the soil in the off-season for an area of farmland. Therefore they benefit farmers by providing a better yield the following season. And wild oats were brought as a food source for livestock, so they benefitted ranchers by having something to feed their animals. And technically, they’ve benefitted people like me who get paid to remove them. But the amount money the government spends on removing invasives for wildfire prevention, flood control, and erosion control is extreme! The California Invasive Plant Council claims $82 million is spent on invasive plant removal in California annually. Here’s a link to the informational brochure I found it in.

The most effective ways to remove invasive species depend on the species, area of land, and the amount of funding available. I’m sure there are other factors I’m missing, but this is just off the top of my head. Because all these factors play a role, I don’t think I can say any one type of control is the best. I will however, tell you about my favorite.

Community based, volunteer powered, habitat restoration what my background is in and I love it. I feel that empowering the community to participate in a restoration project gives them a feeling of ownership and respect for that piece of land. The more people that feel protective over an area of land, the less chance it will have of being degraded again in the future. It also is more cost effective for a project to have few paid staff (like me), that are trained to lead people volunteering (not paid) their time. Some projects are even completely volunteer run, meaning no one is getting paid. And best of all, the people that volunteer will take what they learn home and: remove invasives around their home, make more educated decisions with their landscaping, and even might teach their friends and family a thing or two.

This is a difficult one, since I spent most of my invasive plant removal in the bay area. But they are a few I have come in contact with here.

In the literal sense of the word dangerous, castor bean plant is the most dangerous. I’m pretty sure the seeds are the most poisonous thing in the world. However, if you don’t ingest the seed you’re fine. So the chance of it poisoning you is actually practically non-existent.

As far as most dangerous in an invasive sense, it depends on the habitat. Inland form the coast and in the foothills, various mustards are definitely the worst. Sahara mustard is the worst of them. In waterways, giant reed (Arundo donax) is a really bad one that can cause many issues. And on the coast, Pampas grass and “highway iceplant” threaten native habitat.