Fact vs. Fiction: The real threats to native plants in California

The enduring fiction of the native plant movement is that the existence of non-native plants threatens the existence of native plants by “crowding out” native plants.  If that were true, we should expect to see some evidence of such a causal relationship after 250 years of steadily increasing numbers of non-native plant species.  But we don’t. 

Marcel Rejmanek (UC Davis) is the author of the most recent report on plant extinctions in California, published in 2017.  At that time there were 13 plant species and 17 sub-species native to California known to be globally extinct and another 30 species and sub-species extirpated in California but still found in other states.  Over half the globally extinct taxa were reported as extinct over 100 years ago.  Although grassland in California had been converted to Mediterranean annual grasses by grazing domesticated animals decades before then, most of the plants now designated as “invasive” in California were not widespread over 100 years ago.

Most of the globally extinct plant species had very small ranges and small populations.  The smaller the population, the greater the chances of extinction.  Most of the globally extinct plants were originally present in lowlands where most of the human population and habitat destruction are concentrated. Although there are many rare plants at higher altitudes, few are extinct.  Plants limited to special habitats, like wetlands, seem to be more vulnerable to extinction. The primary drivers of plant extinction in California are agriculture, urbanization and development in general.

Non-native plants are the innocent bystanders to disturbance

“Invasive species” are mentioned only once in the inventory of extinct plants published by California Native Plant Society and only in combination with several other factors. However, the identity of this “invasive species” is not clear.  Rejmanek suggests that the “invasive species” rating refers to animal “invasions” by predators and grazers.  He says, “Indeed, one needs quite a bit of imagination to predict that any native plant species may be driven to extinction by invasive plants per se.” (1)

Although climate change is not cited as the cause of any of the known plant extinctions in California, Rejmanek predicts that climate change is likely to be a factor in the future, not only because of the impact of drought and higher temperatures, but also because non-native plants may be better adapted to changed conditions.

There are over 1,000 naturalized non-native plant species in California.  Their presence is associated with human disturbance.  Naturalized non-native plants are a symptom of disturbance, not the cause.  The impact of non-native plants on native plants cannot be separated from other factors that created the conditions for success of non-native plants.

Specialized insects are exaggerated

Another popular fiction among native plant advocates who love to hate non-native plants is that specialized insects—especially pollinators—require specific native plant species. Again, the record of plant extinctions in California does not support that myth:  “…there is no indication that the loss of pollinators was an important factor in plant species extinctions in California. [For example, one of the native plant species extirpated in California] has many documented non‐specialized pollinators. There does not seem to be any particular dispersal mode associated with presumably extinct plants in California.” (1)

Putting plant extinctions into context

Mediterranean Climates are found in coastal temperate zones. Mediterranean climates are characterized by hot dry summers and mild wet winters.

Setting sub-species aside, there are 5,280 identified native plant species in California and 28 known extinctions of native plant species, including 15 plant species known to still exist in other states.  Only .53% of California native plants are known to be extinct in California, about one-half of one-percent.  Does that seem like a lot?  Rejmanek compared the extinction rate in California with other Mediterranean climates.  The extinction rate of native plants in California is similar to those in the European Mediterranean Basin, South Africa, and Australia, but a little greater than the rate in Chile, where there are fewer endemic plants that exist only in Chile.  Endemism is associated with small native ranges and small populations that are more vulnerable to extinction.

Why are there many endemic plants in California?

About 40% of native plant species in the California Floristic Province are endemic, found only in California and in most cases only in small areas within California, including our off-shore islands.  Their small populations in isolated geographic areas, sometimes within unique ecosystems, such as alkaline sinks, make them particularly vulnerable to extinction.

The evolutionary history of endemic plant species explains why there are so many in California.  Endemic plants are close relatives to plants that exist elsewhere and are sometimes plentiful where they came from.  For example manzanita is a genus of chaparral shrub that is plentiful in California, but there are also many rare endemic manzanita species that occur only in small areas and small populations.  There are several endangered manzanita species in the Bay Area (pallid, Raven’s, Franciscan).

Franciscan manzanita is one of 2 endangered manzanita species in San Francisco. There is one individual plant left of each of these two manzanita species. There are many endemic plants and insects in San Francisco and several are now extinct. San Francisco has a complex, diverse geology and topography and it is surrounded on 3 sides by water, creating many small, isolated microclimates in which many endemics have evolved.

The geography of California explains why the evolution of a plant species diverged from its plentiful ancestors to become an endemic species in a small geographic area.  Plants move around in a wide variety of ways, most natural, without the aid of humans.  Their seeds are dispersed by animals and birds that eat them or inadvertently carry them to another location.  Sometimes their seeds are carried on the wind or brought to islands by storms and currents.

When a plant arrives in a new location that is isolated from its original home and therefore cannot mate with its relatives, it begins its own, independent evolutionary history.  Each successive generation is reacting to its new environment, rewarding its fitness with its new home with a successful new generation.  Each generation rolls the genetic dice, its genome drifting away from its ancestors in a random way.  Occasionally a mutation will occur that alters the evolutionary trajectory.  Eventually, the plant in its new home is sufficiently genetically distinct that taxonomists are ready to call it a separate species.  Naming a new species is a judgment call, often questioned by some taxonomists, called “lumpers” as opposed to the “splitters” who are ready to name it a new species.

The factors that result in endemic species are many, but broadly speaking they are mobility and, ironically, isolation.  California is one of the most geographically diverse states in the country, with corridors for mobility, but many barriers that create isolation.  Gordon Leppig describes California’s geographic diversity in Beauty and the Beast:  California Wildflowers and Climate Change, published by California Native Plant Society:  “The state’s natural wonders include five deserts, the highest and lowest points in the continental United States, the third-longest state coastline (about one thousand miles), the most national parks (nine), the most federally designated wilderness areas (more than 140), the highest percentage of wilderness in the contiguous United States (14%), the most diverse conifer assemblage outside the Himalayas, the most federally listed species….”  The multitude of different ecosystems with unique microclimates produces one of the most diverse floras in the world.

Click on the picture to watch the movement of tectonic plates over one billion years. Watch California slowly emerge as the jigsaw puzzle takes shape. California is the edge of two tectonic plates that collide and grind past one another perpetually, uplifting and dropping the land into fractured geomorphic pieces.

Human activities penetrate the barriers that created genetic isolation in the past.  Our roads become corridors for the biological exchange that threatens small, isolated pockets of rare plants.  Trade and travel has ended the isolation of off-shore islands.  Our roads and dams also create new barriers for mobility.  In other words, we are altering pre-settlement corridors and creating new ones.  We should expect consequences for our ecosystems for the changes we have made.

Given the number of rare and endemic plants in California and the changes in the environment required to accommodate nearly 40 million human Californians, it seems that extinction of less than one-half of one percent of native plants is a surprisingly small loss. 


(1) Marcel Rejmanek, “Vascular plant extinctions in California: A critical assessment,” Diversity and Distributions, Journal of Conservation Biogeography, 2017

Spartina eradication: Herbicides are their dirty little secret

This is a good news/bad news story about the eradication of non-native Spartina marsh grass and the impact it has had on the population of endangered California Clapper Rail:

  • Spartina alterniflora, Smooth Cordgrass.  USDA photo
    Spartina alterniflora, Smooth Cordgrass. USDA photo

    The good newsUS Fish & Wildlife has temporarily halted efforts to eradicate non-native Spartina (Spartina alterniflora) in the San Francisco Bay Area because the population of endangered California Clapper Rail has declined by 50% during the period of eradication efforts from 2005 to 2011. (1)  This problem was identified several years ago and was attributed to the lack of cover for the rail as a result of eradication of non-native Spartina, which grows more densely, taller, and doesn’t die back in winter as the native Spartina does. (2)

  • The bad news:  US Fish & Wildlife attributes this negative impact on the Clapper Rail population on the slow recovery of native Spartina (Spartina foliosa). 
    Spartina foliosa - USFWS
    Spartina foliosa – USFWS

    They do not acknowledge that non-native Spartina provides superior cover compared to the native species.  Nor do they acknowledge that non-native Spartina was killed with herbicides.  Therefore, they do not consider the possibility that the slow recovery of native Spartina may be attributable to the herbicides that were used to kill the non-native plant.  They also continue to claim that the recovery of the endangered California Clapper Rail depends upon the return of native Spartina, despite the overwhelming evidence to the contrary.  The California Clapper Rail is a sub-species of Clapper Rail; the Clapper Rail is abundant on the East and Gulf Coasts and not endangered perhaps because of the superior cover provided by Spartina alterniflora on those coasts. (3)  Based on these fictions, US Fish & Wildlife proposes a new strategy that will simultaneously eradicate non-native Spartina while intensively planting native Spartina.  (1)

We have been following the Spartina eradication project since 2011.  For the benefit of new readers, we will review the issues with a few excerpts from previous posts on Million Trees.

Spartina alterniflora:  Treasured on the East Coast, reviled on the West Coast

Spartina alterniflora (Smooth Cordgrass) is a species of marsh grass native to the Atlantic and Gulf coasts of the United States, where it is considered a valuable plant making important contributions to the coastal ecology:

  • Its dense growth provides protection against storm surge and “erosion control along shorelines, canal banks, levees, and other areas of soil-water interface.” (4)
  • It filters nutrients, sediments and toxins from the water that flows off the land before reaching the ocean, acting as a natural water treatment facility.
  • It provides cover and food for birds, mammals and marine animals that live in the coastal marsh.

Where Smooth Cordgrass has died back in its native range, the dieback has been considered a serious environmental threat:

  • In 2001 the Governor of Louisiana declared a “state of emergency” when Smooth Cordgrass declined and the state obtained $3 million of federal funding to study and hopefully reverse the decline.  This study resulted in the development of a method of aerial seeding of Smooth Cordgrass to restore declining areas of marshland. (5)
  • A similar, but smaller dieback of Smooth Cordgrass in Georgia led to a collaborative research and on-going monitoring effort by 6 research institutions in Georgia.
  • Similar dieback of Smooth Cordgrass has been reported as far north as the coast of Maine.  A researcher at the Connecticut Agricultural Experiment Station is quoted in that report as saying, “In New Orleans, if their marshes were intact, the storm surge of Katrina would not have reached the levees.” (6)

 The war on Smooth Cordgrass on the West Coast

Smooth Cordgrass is not native on the Pacific Coast of the United States.  Therefore it is treated as an alien invader to be eradicated with herbicides:

  • $24 million was spent to eradicate Smooth Cordgrass in San Francisco Bay and Willapa Bay from 2000 to 2010 (7)
  • $16.3 million is projected to be spent on the entire West Coast from 2011 to 2020 (7)

Spartina is being eradicated with an herbicide, imazapyr.  This is a new herbicide about which little is known.  The analysis that was done to justify its use in the Spartina eradication project admits that no studies have been done on its effect on shorebirds, including the endangered Clapper Rail. 

The Material Safety Data Sheet mandated by the Environmental Protection Agency tells us that imazapyr is “not readily biodegradable.”  So, in the event that we eventually learn that this herbicide is harmful to shorebirds and/or to us, we probably should assume that it will still be in the environment in the nearly 200 sites in the San Francisco Estuary on which it has been sprayed.  Imazapyr is also being sprayed–sometimes from helicopters–in hundreds of places along the West Coast, including Oregon and Washington.

Imazapyr is often mixed with glyphosate by the Spartina eradication project.  Glyphosate is a non-selective herbicide.  That is, it kills any plant it is sprayed on at the right stage of its growth.  But imazapyr is far more insidious as a killer of plants because it is known to travel from the roots of the plant that has been sprayed to the roots of other plants.  For that reason, the manufacturer cautions the user NOT to spray near the roots of any plant you don’t want to kill.  For example, the manufacturer says explicitly that imazapyr should not be sprayed under trees, because that tree is likely to be killed, whether or not that was the intention. 

Furthermore, no tests have been conducted on the toxicity of combining multiple pesticides in a single application.  Therefore, we know nothing about the possible synergistic effects of combining imazapyr and glyphosate. 

These facts about the herbicides used to eradicate non-native Spartina bear repeating.  The main herbicide being used is known to be mobile in the soil and persistent in the environment.  The herbicide with which it is often mixed is an indiscriminate killer of any plant on which it is sprayed.  Therefore, the likelihood that these herbicides will prevent the establishment of the new plantings of native Spartina should be taken into consideration.  The entire enterprise seems deeply flawed, both harmful and futile. 

Bringing it home to the Bay Area

So, what does this have to do with you?  If you are concerned about pesticide use, you might be interested in the fact the East Bay Regional Park District (EBRPD) used 203 gallons of imazapyr in 2009 and 121 gallons in 2010 for the sole purpose of eradicating Spartina on their properties.  We don’t know how much imazapyr EBRPD used in 2011, 2012 and 2013, because they haven’t published a report of pesticide use since 2010.  Since their properties are only on the east side of the San Francisco Bay, we should assume that at least that much imazapyr was used by land managers on the west side of the Bay.

 Displacement of Clapper Rails in San Francisco

California Clapper Rail.  British Wikipedia
California Clapper Rail. British Wikipedia

In July 2011, a Clapper Rail was seen and photographed at Heron’s Head in southeastern San Francisco.  There was quite a bit of excitement about this sighting because a Clapper Rail had not been seen in San Francisco for decades.  That excitement dissipated when we learned more about where this bird came from, which provided a probable reason for its arrival.

The Clapper Rail was wearing a radio collar that had been put on him and 109 other rails by the USGS to track their movements.  He had moved from Colma Creek, 11 km south of Heron’s Head, which is one of nearly 200 Spartina “control sites” in the San Francisco Estuary.  The bird sighted at Heron’s Head is one of three Clapper Rails that have left Colma Creek since 2007, when the radio collars were placed.  The Spartina control project has been going on for over 10 years, so we have no way of knowing how many Clapper Rails were displaced prior to 2007.  In 2012, non-native Spartina at Heron’s Head was sprayed with herbicides.  Where did the Clapper Rails go from there?  Was there anywhere left for them to hide?

Pesticide Application Notice, Heron's Head, 2012
Pesticide Application Notice, Heron’s Head, 2012

As our readers know, native plant advocates claim their “restoration” projects benefit wildlife.  They can offer no evidence for this claim.  But there is considerable evidence that proves them wrong.  The endangered California Clapper Rail is one such case.


(1)     Adam Lambert et.al., “Optimal approaches for balancing invasive species eradication and endangered species management,” Science, May 30, 2014, vol. 344 Issue 6187

(2)     “West Coast Governors’ Agreement on Ocean Health, Spartina Eradication Action Coordination Team Work Plan,” Released May 2010, page 12

(3)     Cornell Ornithology Lab:  http://www.allaboutbirds.org/guide/clapper_rail/id

(4)     “Smooth Cordgrass,” USDA/NRCS Plant Fact Sheet.

(5)  Dorset Hurley, “Geogia’s Marsh Die Back and Louisiana’s Marsh Browning,” Altamaha Riverkeeper

(6)  “What’s killing off our salt marshes,” Going Coastal Magazine, September 15, 2008

(7) “West Coast Governor’s Agreement on Ocean Health,” May 2010, page 5-6