Introducing a new series: Flora and Fauna Non Grata—my work with invasive species

First, we discuss what invasive actually means

June 6-14 is California Invasive Species Action Week. This seems like an opportune time to launch a new series, Flora and Fauna Non Grata, about invasive species. As with the In Touch series, which focused on native species, now I plan to write about invasive species I have worked to control or have had some experience with, although I will include other invasives as the series develops. I enjoyed putting together the In Touch posts and hope you enjoyed reading them. I will continue them, but since I have covered most of the native species I have worked with, that series will be winding down a bit.

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First, to be sure we’re on the same page, let’s talk about what an invasive species is and is not. Let’s get our terms straight about what is meant by an invasive species and how that differs from a nonnative species.

When I teach interns, volunteers, and students about invasive and nonnative species, I tell them that we are going to dig into our Plato and Schopenhauer and study philosophy, because these questions and definitions have less to do with how you measure or quantify something and more to do with how you think about it.

A nonnative species is any living organism that is found outside its historic range. These do not necessarily cause harm to their new environments. In San Diego, where I live, an example of a harmless nonnative species is the Moreton Bay fig tree. Native to Australia, these trees have been planted here for more than 100 years. Huge, old ones grow in our Balboa Park. These trees are from elsewhere, but they don’t spread into other areas and cause no environmental or ecological problems. Moreton Bay fig trees are a nonnative species in Southern California. They are not invasive.

How far away is far away?

That’s pretty straightforward. Moreton Bay fig trees are native to another continent on the other side of the world. But how far away does a species have to travel to be considered nonnative? Lots of folks in Southern California plant Saint Catherine’s lace, a buckwheat native to the Channel Islands, which are 20 to 50 miles off the coast of California. These buckwheat plants wouldn’t be here unless people planted them, but they naturally occur on islands just over the horizon. Not naturally here, but naturally occurring only 50 miles away. Native? Nonnative?

At the zoo where I work are Tecate cypress, endangered trees that naturally occur on Otay Mountain, ten miles away. They do not naturally occur along the coast, where the zoo is found. So are they native or nonnative to the zoo’s landscaping? They wouldn’t be growing at the zoo if we hadn’t planted them, but from the zoo I can see the mountain they grow on. That’s how close naturally occurring groves are. Native? Nonnative?

What if the organisms move on their own?

Organisms change their ranges all the time, expanding into new areas and abandoning old ones. Birders in particular will note and document bird species moving or expanding ranges. If they naturally move on their own accord, a perfectly natural thing to do, are they native to their new lands or waters?

But what of organisms moving into new territory because of human activity? The Texas armadillo has been extending its range northward for generations, due mostly to human activity. And the Baltimore oriole and other birds are shifting their ranges because of human-induced climate change. These creatures have moved into new territory because of us humans. They probably would have kept their old addresses if it wasn’t for us. Are they native or nonnative in their new landscapes?

Invasive species

Invasive species are nonnatives that are harmful. When I talk to folks here in San Diego, one example of an invasive species I like to give is mosquitos. When I moved here, decades ago, mosquitos were virtually unknown, and I was glad to be free of the pests I grew up with in Appalachia. Now, getting bit by a mosquito in Sa Diego is a common occurrence. As with much of the rest of the world, we have been invaded by Aedes, tropical mosquito species that can spread diseases. These certainly fit the criteria for invasive: from somewhere else and harmful.

Ecologically, invasive species harm native species. They can do this in a lot of ways. They can outcompete native species for food, disrupt reproductive cycles, or push out native organisms from their territory. They can spread disease, like mosquitos. They can reduce the numbers of native species by just eating them up.

That’s pretty easy to understand. We get back into the realm of Aristotle and Kirkegaard when we distinguish nonnative and invasive sometimes. Invasives vary as to the amount and type of harm they can cause, as well as how humans view those harms. Invasive species that attack food crops are taken quite seriously by farmers, as well as local, state, and federal governments. No matter the extent of the harm, a lot of resources are spent to eradicate or control for agricultural invasive species. In these cases, few people shy away from calling these pests invasive.

There are nonnative species that are slightly problematic. Introduced to much of the rest of the world from Europe, the house sparrow may be a good example of such an invasive species. They are disruptive, as they take over nesting cavities used by native birds. House sparrows avoid grasslands and woodlands, however, preferring urban and suburban environments. This behavior limits the harm this species poses to native birds. They are harmful, but only so much.

There are people, and I know a good number of them, who say there are no invasive species or that folks like me make too much of the harm they cause, that we make mountains out of invasive molehills. Well, I disagree and hope I can introduce and clarify several concerns about invasive species as this series continues. If you have questions or comments, please hit the “Leave a comment” button below. I’m eager to hear from you.

Previous Green Dispatches on invasive species: