When I first came to live in California, I was awed by the abundance, beauty, and diversity of plants—so many were new and exotic to my eyes. I loved the oaks scattered across golden hills, the redwood groves, madrone, and manzanita. I also loved the towering stands of eucalyptus, the waving plumes of pampas grass, the carpets of iceplant blooming magenta along miles of coastal highway. Decades passed before I learned that many of these plants were not only as alien to California as I, a Midwesterner, but—more importantly—they were causing serious harm to California’s native plants and wildlife.

Take eucalyptus. Its blossoms gum up the nostrils of songbirds gathering nectar—and that’s just one of its many impacts on the ecosystem. Pampas grass sucks up so much water and grows so fast that natives cannot compete; and that thick green carpet of iceplant eliminates nearly all other plants except oxalis, another invader.

Released from the natural constraints of their native ecological niches, many imported plants proliferate and disperse rapidly, use a disproportionate amount of water, and replace local plant communities with monocultures, thereby depriving native wildlife of the shelter and nourishment they require.

Because of their destructive effects, millions of dollars have already been spent on efforts to extirpate various invasive plants in California, and much more money, time, and hard work will be needed to keep them at bay, especially in areas where native ecosystems are being restored.

Meanwhile, new species continue to invade coastal lands and waters. Among recent arrivals are Atlantic cordgrass, which is spreading in San Francisco Bay and along the North Coast, and Caulerpa taxifolia, the “killer alga,” which—we hope—has been successfully defeated soon after its arrival.

Cordgrass Blues

One recent afternoon, a three-person force confronted a newly discovered clump of Atlantic cordgrass (Spartina alternifolia) in Bolinas Lagoon. This tall, sturdy marshgrass comes from the East Coast, where its dense growth helps stabilize habitats that are scoured by intense seasonal storms. However, on the West Coast it behaves like a ruthless imperialist, outcompeting and hybridizing with the slower-growing, smaller native variety and colonizing marshes and mudflats at the expense of native cordgrass, pickleweed, and wildlife. In the mild West Coast climate, S. alterniflora’s dense clumps spread and merge into meadows, clogging channels and impeding the movement of birds and animals.

This alien was introduced into San Francisco Bay by the U.S. Army Corps of Engineers in the early 1970s as part of a marsh restoration project. By the ’90s it had spread 15 miles both north and south, and biologists realized that it had become a serious problem, threatening to radically transform Bay habitats. Now the San Francisco Estuary Invasive Spartina Project, a multi-agency task force, is planning a massive eradication campaign. Spartina invasions in and near the Bay have been mapped and studied, but during the years of preparatory work—planning, organizing, compiling reports, and securing permits—the grass has continued to spread. At present the Spartina Project can only advise local resource agencies on how best to prevent its advance.

On this particular day, wetland biologist Katy Zaremba and field operations manager Erik Grijalva met with Ari Golan, Supervising Open Space Ranger for the Marin County Open Space District, at the southern end of Bolinas Lagoon, near Stinson Beach. Their target was a clump of alien Spartina that Zaremba had recently spotted while driving along Highway One. S. alterniflora grows taller, with stalks thicker than those of the native S. foliosa and, unlike the native, often has reddish corms (thickened underground stems). By studying its growth pattern and density, she estimated that it had been there for three or four years. Apparently, it had been missed on the mapping survey the Spartina Project had conducted in 2001. The survey had turned up only a single clump of S. alterniflora in Bolinas Lagoon, at its north end (which is part of the Point Reyes National Seashore). That one had been dug out, but today’s subject clump (which is in the Open Space District) had been judged too large to remove easily and completely by digging, so it was to be smothered under a vinyl tarp.

Earlier that morning, Golan had cut down the two-foot-tall shoots. Now the entire clone—a dense circle of about 60 square meters—would be covered with the black tarp, which would absorb solar heat, raising the temperature beneath to effectively “cook” the plant, as well as depriving it of light and oxygen. This “solarization” is expected to kill even the roots and rhizomes. If the tarp stays in place for a year the plant should be gone, because cordgrass seed is viable for only eight months. There is always the possibility, though, that runners have already traveled beyond the area to be covered. Local volunteers and agency staff will be monitoring the site.

I met the team at a highway turnout, where the vinyl had been spread on the ground so grommets could be installed around its edges before the trek into the marsh. “I was very surprised when I saw this plant on my way home,” said Zaremba, who lives nearby. “How could we have missed something this big almost in my backyard?” She figured that it had been revealed by the removal of vegetation that had hidden it.

Carrying the tarp, rope, stakes, and hammers, we moved through cattails and thistles, and into pickleweed marsh interspersed with rings of native cordgrass. The alien Spartina was conspicuous, even with its stalks cropped: its growth was far denser.

“We call this a clone,” Grijalva said. “One plant sends out runners that put up shoots in a roughly circular pattern. All the shoots are genetically identical, so DNA testing can tell us not only what species it is, but, we hope, where it came from.” The team unfolded the tarp, centered it over the plant, and tied loops of rope through the grommets. To hold the cover in place, they hammered yard-long stakes through the loops and deep into the marsh mud. An hour later the job was done. “We hope this will work,” Zaremba said. “It will do some damage to the other plants that are covered, but it has less impact than using herbicides, and it’s a lot easier than trying to dig it up.”

Before leaving, Zaremba took samples of plant matter from the site and from nearby native cordgrass for DNA testing, which would determine whether the removed plant was S. alterniflora or something even more problematic—a hybrid with the native. “There’s just enough overlapping of the flowering periods of the two plants that they can fertilize each other, and the hybrids have the hardiest traits of both species, so they outcompete the original strains,” she noted.

The tests might also show where this particular plant came from. Spartina can propagate either by dispersing seed into the water or by sprouting from pieces of root or rhizome. “This plant could have come from almost anywhere,” Grijalva added. “Bits of root can stick to muddy boots, dog hair, boat bottoms, and travel a long way.”

The Spartina team had one more task: to check the site of the north lagoon clump. Sure enough, a score or more of new S. alterniflora shoots had sprung up from remaining subsurface plant matter. Even single stalks were easily distinguishable from the native cordgrass, which is more slender, smaller, and sparser than the invader. Grijalva pointed out the reddish tint on some of the corms.

Helping to pull up the young stalks gave me a new appreciation of the challenge. They were tenacious, and it was easy to miss fragments left behind.

This kind of intensive labor is a holding action, meant to keep S. alterniflora from spreading beyond the Bay region before a comprehensive attack on the plant can be launched. The worst infestations are in the central parts of the Bay, between the Bay and Dumbarton Bridges, where it was first planted. Three other alien invasive cordgrass species have been found around San Francisco Bay: S. densiflora and S. anglica near Corte Madera, and S. patens near Benicia. Those infestations are relatively small and isolated, so there’s a good chance that they can be eradicated.

The larger effort must wait until all the required environmental documents and permits are secured. That could be within the next few months, according to Maxene Spellman, project manager for the Coastal Conservancy, which is leading the multi-agency task force. The treatment must be done within a small annual window of time determined by the breeding and nesting seasons of the endangered California clapper rail and other natural constraints. Over $3 million has already been committed to the Invasive Spartina Project.

The Monster Reed

The deliberate introduction of Spartina alterniflora into San Francisco Bay, though well-intentioned, now looks like a colossal error. In hindsight, some wonder how such a mistake could have been made, given the key evolutionary concept that species evolve in relation to all the other species that share their ecosystems. But humans have always moved plants and animals—domesticating and breeding them to suit their needs, then taking them along wherever they have gone. In most cases, that hasn’t been a problem. Most food crops and garden plants stay where they’re wanted.

Trouble comes when plants that are introduced for a particular purpose turn out to have dire impacts in the long run. Arundo donax, the giant reed, was brought to California from Spain in the 1820s because of its many practical uses. It produces abundant material for thatching, fencing, basketry, and fishing rods, and is also cultivated for the making of reeds for woodwind instruments. In its native habitat, it is planted to keep stream banks from eroding. Here, however, outside its ecological niche, it has become a monster. In southern California, settlers apparently carried it high into watersheds, and it spread rapidly downstream, creating dense monocultural thickets. It usurps huge quantities of water, chokes out trees and other native plants, is extremely flammable, and destroys riparian habitats that support many birds and other wildlife. Yet A. donax itself provides neither food nor nesting places for these creatures.

To defeat this invader seems as difficult as keeping sand from being swept out to sea from beaches. Like S. alterniflora, A. donax tends to spread and grow back at least as fast as it can be removed. In California its seed is sterile, but because it can reproduce from bits of vegetable matter, even very thorough methods may not prevent regrowth. It grows up to 30 feet tall, by as much as two inches a day, with root masses up to a yard thick, from which pieces break off—especially during floods (or removal efforts)—and wash downstream where they can start new plants.

Arundo donax is now the most despised plant in coastal southern California, having infested most coastal rivers and many of their tributaries. It has also become a problem in the Sacramento, Russian, and Gualala Rivers, and other streams in northern California. During the past decade, millions of dollars have been poured into Arundo eradication efforts, yet it continues to advance.

The situation is not altogether hopeless, however. In San Diego County, the Mission Resource Conservation District began attacking Arundo in the early 1990s, and has successfully eradicated the plant from the Santa Margarita River watershed above Camp Pendleton. It is now ready to shift its operations to the San Luis Rey River. “You have to start at the top and work downstream,” said project coordinator Jason Giessow, “because every time there’s a big flood, it shuffles the whole ecological deck. We’ve shown that the watershed approach is effective.”

The best way to attack Arundo, according to Giessow, is to spray Rodeo (glyphosate— the only herbicide approved by the EPA for wetland use) on the foliage in the fall, as the plant prepares for winter. The poison is drawn down into the roots, killing the entire plant. Three or four months later, the remaining biomass is mowed or cut down and left as mulch, to help riparian vegetation to get reestablished. “We basically trick the plants,” he explained. “We don’t disturb the root mass, which would trigger new sprouting.” Other methods, ranging from cutting to bulldozing to grazing by goats, tend to be considerably more costly and labor intensive, and less likely to stop stem nodes or rhizomes from washing downstream.

“Arundo seems to be unique among invasive plants, in that it brings everybody to the table,” Giessow said. “Private landowners are concerned about the flooding and fire risk that it causes. Normally, riparian corridors stay green all year and help keep fires from spreading, but Arundo acts as a kind of wick, that actually can spread fires faster. We’ve had amazing participation.”

Meanwhile, as the battle against Arundo continues in California, an entrepreneur has proposed planting 200 acres of it in Florida as a source of paper pulp. This is certainly a viable use of Arundo biomass—thatched roofs are no longer very popular—but to those who know the California story, the possibility that the plant might escape into Florida’s vast wetlands is appalling.

Green Death

The discovery of the “killer alga” Caulerpa taxifolia in California waters in 2000 set off the most sensational invasive plant ado to date. As soon as the invader was recognized, concerned scientists made sure that its story was well-publicized, so that immediate action would be taken to deal with the threat. A significant part of the Caulerpa tale is that after its discovery in the Mediterranean, warnings were not taken seriously until it had spread explosively, significantly damaging sensitive habitats, perhaps past the point where it could be controlled. In California, said Bob Hoffman, Southern California Environmental Coordinator for the National Marine Fisheries Service, “everyone was determined not to let that happen. There was a multi-agency push for instant action—let’s just get rid of it!”

The largest California infestation, in Agua Hedionda Lagoon in San Diego County, covered as much as 11,300 square feet at its peak. Immediate emergency treatment—patches were covered with plastic enclosures that were then injected with chlorine—combined with extensive educational efforts, seem to have been successful. No C. taxifolia has been found in Agua Hedionda Lagoon since September 2002, and none in Huntington Harbor (the second, much smaller California infestation) since November 2002. “As far as we know, this was the only successful marine alga eradication project in the world,” said Hoffman. “All the others made the decision to act too late, so they entered control mode. That’s what happens with most invasive species programs.”

This highly invasive strain of tropical seaweed was developed in Germany for saltwater aquarium use, then widely distributed to European marine aquaria. It most likely entered the Mediterranean when tanks were flushed at the Oceanographic Museum of Monaco. From the square-yard patch reported there in 1984, C. taxifolia has spread to cover about 32,000 acres off the coasts of Spain, France, Monaco, Italy, Sardinia, Croatia, and Tunisia. This invasive Caulerpa tolerates much colder water than the original, and grows on almost any kind of seafloor. It grows fast and spreads rapidly, outcompeting native species and creating a monoculture carpet, eliminating seagrass meadows that many creatures depend on for survival. As the alga can reproduce from fragments as small as one millimeter in length, even infestations that seem to have been eradicated must be continually monitored to prevent recurrence. The qualities that made the alga desirable for aquaria turned out to make it an extremely successful invader, and it was likely introduced into California waters as it was into the Mediterranean—by an aquarist flushing a tank.

The rapid response to the California Caulerpa infestation included legislation that now prohibits the sale, possession, import, transport, and release of Caulerpa taxifolia in the state. The threat is far from over, however, as many home aquarists must still have the alga in their tanks, some of which may eventually find its way into state waters. Hoffman says that the Southern California Caulerpa Action Team is putting together a program to educate the public, including aquarists and their suppliers, about the dangers of this Caulerpa strain, while the Department of Fish and Game has organized a team of senior volunteers in San Diego to monitor stores. Any coastal construction or restoration projects must now include Caulerpa searches in order to get permits.

Beautiful Banes

One reason that invasive alien plants are so difficult to control is that people are very fond of many of them.

When word of Caulerpa taxifolia’s appearance in California first reached Coast & Ocean in 2000, I did a web search on the name. Much to my surprise, there were almost as many sites that advertised the alga for sale for use in home aquaria as there were sites that reported its invasive impacts in the Mediterranean. I even stumbled onto a chat room where some home aquarists were wondering how to get rid of “feathery caulerpa” in their tanks, while others were begging for samples. Much has changed since then. Now even aquarists who had been harshly critical of the proposed ban have calmed down, and I no longer find it for sale on line.

On the day I joined the Spartina expedition, by the highway I could see ice plant, scattered tufts of pampas grass (or, more likely, jubata grass), and invasive brooms. Eucalyptus and invasive oxalis grow nearby. I was surrounded by many of the most troublesome alien plants in California. Have we already lost the battle against the green invaders?

On the Spartina front, Zaremba, Grijalva, and Golan were all at least slightly optimistic. They find that volunteers who help remove invasives tend to become well-informed proselytizers, spreading the word to others. In the Bay Area, at least, they see a growing awareness of the problem and a willingness to help do something about it.

On the other hand, who knows what invader may turn up next?

Many people believe that none of this is a problem, that it’s man’s destiny to transform the face of the planet, and that we should accept altered environments as inevitable. Humans and their works are as much a part of nature as anything else, after all, and we have no idea into what we may be evolving.

Once we gain some awareness of these invaders, however, it’s easy to observe what happens when we ignore the impacts of our actions or surrender to apparently overwhelming forces. We find ourselves in the midst of a monoculture, where diversity is lost, and only the most aggressive competitors can survive—whether they have anything to offer to the rest of us or not.

The print version of this story includes information on these other invasive species: eucalyptus, oxalis, pampas and jubata grass.

CLICK HERE for sources of Invasive Plant Information on the Internet