Contradictions of the native plant movement

In a recent article in Bay Nature, the author tells the story of two California native trees and proposes to answer the question, “Now the question is, where do [these trees] belong?”  It’s a thorny question and one that illustrates one of the contradictions of the native plant movement.

The definition of “native” in California is based on the arrival of Europeans near the end of the 18th century, specifically 1769 in the San Francisco Bay Area.  Wherever plants or animals lived in 1769, they are considered native in the Bay Area.  If they were introduced or arrived after 1769, they are considered non-native, and in many cases designated as “invasive.”  Status as “invasive” makes them targets for eradication.

Monterey pine is a case in point. It has a small native range around Monterey, California, just 115 miles south of the East Bay. It was widely planted in the Bay Area by early settlers because the climate is similar to Monterey and much of the Bay Area was treeless. It is well adapted to conditions and thrives here.  Yet, it is being eradicated by most public land managers in the Bay Area because it is, strictly speaking, non-native according to the official classification of non-natives.

Bird’s eye view of San Francisco in 1868. US Library of Congress.  About half of San Francisco was treeless sand dunes before early settlers planted the non-native trees that now live there.

There is fossil evidence that Monterey pine has lived along the coast of California many times in the past, far outside its small present “native” range.  The evidence of its prehistoric past in the Bay Area has not saved it.  It wasn’t here in 1769, so it’s gotta go to suit the purist agenda of our public land managers.

But, wait!  Maybe our public land managers don’t have such a purist agenda. The same public land managers who are eradicating Monterey pine in the Bay Area are also planting Torrey pines and Catalina ironwood, which are native to the Channel Islands, off the coast of Southern California. These tree species weren’t here in 1769, nor were they here in the distant past.  In Monterey, where Monterey pines are native, Torrey pines are considered “invasive,” according to the interview with a tree advocate in Monterey who is quoted by the Bay Nature article.

Torrey pine, San Diego. Wikimedia commons
Catalina ironwood – Catalina Island. Wikimedia Commons

Where I have observed Torrey pines and Catalina ironwood being planted by East Bay Regional Park District and other public land managers, they seem to be doing well. Therefore, I have no objection to their being planted here, although they are not “native” as defined by local native plant advocates. I have one straight-forward criterion for “where trees belong:” they belong where they will survive.

The author of the Bay Nature article demurs, “Should we view Monterey pine as unwanted and possibly damaging invaders or welcome them as neo-natives? I couldn’t decide.” That seems to me an easy question to answer:  It makes no sense to destroy healthy Monterey pines that have lived in the Bay Area many times in the past, while simultaneously planting trees that have never lived here. If trees are adapted to present environmental conditions, they should be welcome here.

Nativist Dilemmas

The native plant movement is fraught with conundrums such as the vexing question of where Monterey pine and its close relative, Torrey pine, belong.

  • There are many unresolved debates about exactly where native ranges are. The rusty crayfish is “probably the most reviled crayfish species in North America,” yet there are as many opinions about its native range as there are publications about the species.  Pike is eradicated in Ireland, yet a recent genetic study revealed that there are actually two pike species, one of which is likely native and unique to Ireland.  (1)
  • There is little agreement among invasion biologists about the difference between non-native and “invasive.” Some consider all non-native species potentially invasive, some do not. (1) The California Invasive Plant Council recently designated nearly 100 plant species as invasive (in addition to 200 plants already on the list), despite the admission that they are not invasive in California.  Given that the behavior of plants depends to a great extent on local climate conditions, we cannot assume they will be invasive in California. When a plant is designated as “invasive” it becomes a target for eradication.  It is therefore a designation that should be used sparingly.
  • Public land managers in the Bay Area kill as many native plants as non-native plants because of their goal of recreating the landscape that existed here prior to the arrival of Europeans. That goal requires that early-succession native shrubs be killed when they naturally encroach on grassland if it is not burned periodically or grazed by animals.  Native coyote brush is eradicated as often as non-native broom when it “invades” grassland.  Are we trying to preserve native species or historical landscapes?  Those are different goals and they are often contradictory.

Invasion biology is an ideology, not a science

These—and many other—contradictions are symptoms of a pseudoscience, struggling to make sense, but failing to do so.  Invasion biology made the initial mistake of picking a specific point in time to define the “ideal” landscape.  Because nature is dynamic, in response to a constantly changing environment, the arbitrary selection of a static landscape will always be a source of contradictions.  The environment has changed radically since 1769 and even more radically since the 400-year baseline used on the East Coast.  We cannot expect to recreate that historical landscape because we cannot recreate the environment in which it existed. 

  1. C. Guiasu, C.W. Tindale, “Logical fallacies and invasion biology,” Biological Philosophy, Sept 2018, 33(5)