War of the Weeds

Arundo for miles? Nonnatives threaten to take over wildlands

Invasive weeds-imported plants that hitchhike to new territory and displace native plants-are rolling across our landscape, and no one really knows how to stop them.

What's the big deal about exotic, or nonnative, plants? After all, most of them are benign, even useful. You won't find any objection from Steve Schoenig, president of the California Invasive Plant Council. 'I'm not against exotic plants,' he said. 'I eat them every night for dinner.'

Of all the invasive weeds in Southern California, Arundo grass is the most hated. The plant grows to enormous heights with ferocious speed, causing tremendous damage to ecosystems. photo © John Randall / The Nature Conservancy

Unfortunately, a small percentage of exotics do become invasive, wreaking massive havoc on California's environment. Ice plant, pampas grass, and cape ivy have turned thousands of acres of coastal prairie and sage scrub into sterile monocultures. Yellow starthistle has invaded over 20 million acres of habitat in California, crowding out native plants and degrading wildlife habitat.

'Everyone who knows about yellow starthistle wishes they could go back in time and stop it,' said Ray Smith of the L.A. County Agricultural Commissioner's Office. 'We wish we didn't have it here, but what are you going to do? There is absolutely no hope of eradicating it.'

Little green bulldozers

Superweeds like yellow starthistle are experts at beating the odds. They take up lots of water, nutrients, and space, germinate fast, grow rampantly, and reproduce prolifically. Some produce hundreds of thousands of widely dispersed seeds.
Others clone themselves from the tiniest of stems. Some invasives poison other plants, salt the soil, create flammable leaf litter, or simply smother everything in their path. Spared from the predators, competitors, and diseases that stunted their ambitions back home, they become little green bulldozers.

With rare exceptions, birds, insects, and other wildlife can't adapt to these newcomers. As pavement replaces earth and weeds damage what's left, they have nowhere to go. That's why invasives are hastening the decline of rare and endangered species across the globe.

In the words of NASA, which recently signed on to monitor invasive organisms from space, 'nonindigenous invasive species may pose the single most formidable threat of natural disaster of the 21st century.'

Global weeding

How do the weeds get here? On their own, few are able to overcome the natural barriers of mountains, deserts, and oceans. So they find their way in as contaminants in seed, in shipping materials, on agricultural machinery, or in baggage and mail. Weeds hitch a ride on horses, cars, agricultural equipment, and practically anything else that moves, including the currents of the water and wind. Many invasive plants enter through the nursery trade, which is always looking for the next new thing.

It's hard to know in advance which weeds will take root here. Exotic species can change existing habitat niches and open up new ones, which makes it hard to estimate how they will affect ecosystems. Alarmingly, said Smith of the commissioner's office, 'almost every nonnative organism has some potential to be detrimental to our agriculture and wildlands.' The challenge faced by agencies like Smith's is figuring out which few organisms will have significant impacts and responding quickly enough to keep them in check.

Once the weeds are here, habitat disturbance creates a welcome mat. Disturbing wildland areas opens them up to invasion, like getting a cut opens your skin up to infection. Disturbance can take the form of wildfire, insect invasion, or human activity such as development or off-road vehicle use.

Habitat disturbance isn't a prerequisite for invasion, though. Plenty of weeds propagate independently, moving into completely intact, healthy ecosystems. Changing rain fall patterns and nitrogen deposition from exhaust, courtesy of global warming, make it even easier for invasives to enter unspoiled areas.

That means that protecting lands from development isn't enough. 'On protected lands like parks,' said Schoenig, 'invasive species are the No. 1 threat-not logging or dirt bikes.'

Our wildlands may soon become eerily like our cities, with the vegetative equivalent of Starbucks, Wal-Mart, and McDonald's as far as the eye can see.

Bermuda grass on steroids

What about Southern California-what weeds are the worst here? European grasses, storksbill, and yellow starthistle cover the vastest acreages, but it's Arundo donax that everyone really hates. Arundo, aka giant cane or Arundo grass, grows to monstrous heights, spreads by rhizomes, despoils wildlife habitat, sends segments downstream to take root, hogs sparse moisture, silts up streams, and introduces fires into riparian ecosystems. It's unpleasant to eradicate, and it's ugly.

Three years ago in Santa Clarita, acres of arundo burned to the ground in the Copper Hill fire. Yet within six weeks it was four to five feet tall. 'It's an incredible plant,' said Jim Hartman, acting deputy commissioner for pest management at the Los Angeles County Agriculture Commissioner's office. 'You can literally see it grow. It's Bermuda grass on steroids.'

The county commissioner's office, along with state and national parks and volunteer groups, are waging war on arundo up and down the state-with notable success. Since the Copper Hill fire, the commissioner's office and the National Park Service have eliminated all the arundo in San Francisquito Canyon with foliar spray.

'It's been a great success,' said Hartman. 'At best, you try to reduce the spread of a weed. In this case, we eradicated it.' Progress has been so promising that Schoenig foresees a day when arundo may be gone from the state altogether.

To spray or not to spray?

Arundo brings up divisions within the environmental community over herbicides. Most ecologists, according to Schoenig, acknowledge that herbicides are the only way to go when dealing with large areas. 'Shovels,' he said, 'only go so far.' Yet to many environmentalists, exchanging chemicals for weeds is no bargain.

Schoenig argued that today's herbicides are safe. 'The pesticides used to control wildland plants have been consistently shown in hundreds if not thousands of studies to have no significant impact on human health or the health of wildlife,' he said. 'It may be hard to believe if you're coming from an environmentalist or anti-toxics point of view, but it's true when you look at the science.'

Suzanne Goode, an ecologist with the California State Parks, goes a step further. 'Any concerns people might have about pesticides,' she said, 'are outweighed by the damage being done to the ecosystem by invasive plants.'

She's also not convinced that there is any other way to get rid of persistent re-sprouters like arundo. She cites two removal projects underway in the Santa Monica Mountains: one in Malibu Creek using the herbicide glyphosate, another in lower Topanga Canyon relying on hand methods. The chemically treated arundo is mostly gone; the slashed cane has re-sprouted.

Hand removal can work given enough determination. But there's the issue of volunteer exhaustion. Taking a machete to a 20-foot stand of clumping cane is a Sisyphean task, and Goode noted that fewer people have been coming to the arundo cuttings in recent months.

Opposition to pesticides continues to have positive effects, however, nudging government agencies to adopt integrated pest management practices and galvanizing community ownership of the weed problem.

Biocontrol: A way out?

One increasingly promising solution is biocontrol-releasing a weed's predators into the environment to keep the population in check. In the past, ill-fated introductions of voracious predators hurt more than they helped. But biocontrol horror stories are a thing of the past, said UC Riverside biocontrol expert Mark Hoddle.

Scientists worldwide are busy scouring weeds' home ranges for natural enemies, like insects and fungi, and testing their appetite to make sure they won't prey on anything else. Using molecular tools, researchers are even finding distinct predators for different ecotypes within a single weed species.

The chances of host-specific predators mutating into voracious generalists are microscopic, said Hoddle-natural selection is just too lazy. And biocontrol has a big upside. 'It reduces pesticide usage immensely,' he said, 'and it's not invasive-you don't have to press tractors or large crews of people through fragile environments to spray, burn, till, or rip out the weeds. The bugs can just move in and do the job without leaving a footprint. They work seven days a week for free.'

There have been remarkable biocontrol success stories-beetles were so successful at controlling St. John's wort in Northern California that grateful ranchers erected statues of the six-legged heroes.

Ending the leafy scourge

Never before has there been a more concentrated effort by so many people to fight invasive weeds. The arundo invasion has galvanized people at opposite ends of the political spectrum, bringing together conservationists, farmers, hunters, and private landowners-people who often won't sit down at the same table together.

Almost all counties in California now have a Weed Management Area (WMA), which brings stakeholders together to fight weeds. In the U.S. Congress, a recent amendment to the Plant Protection Act authorized $100 million in funding for WMAs.

Thanks to early detection and response, California has been largely spared from fiendish weeds such as leafy spurge, camel thorn, and hydrilla that are running roughshod over other states. 'It's not exactly a victory,' said California Invasive Plant Council's Schoenig, 'but it could be a hell of a lot worse.'

National publicity has taken off, too, with invasives starring in National Geographic and even Parade, the ubiquitous Sunday-newspaper insert. Articles like April's Discover magazine cover story, a reductionist grab bag of out-of-context quotes that pooh-poohed the invasive species threat, are in the minority.

Schoenig summed it up: 'Invasives are a great outreach opportunity for the environmental community. After all, there aren't many people who are pro-weed. If the Sierra Club and other environmental groups can capture public interest in the issue, they will be able to make new allies and score an environmental victory at the same time.'

Take Action!

• Learn to identify invasive specis, and teach others. Visit www.invasivespecies.gov/plants/alien.
• Remove invasive species from your landscape and replace them with native alternatives.
• Volunteer for California Native Plant Society or the Mountains Restoration Trust
• Avoid using garden plants that may become invasive; think twice before ordering plants by mail.
• Complain to nursery staff when you see invasive plants being sold to the public, especially near sensitive areas.
• Clean your vehicles, bikes, equipment, shoes, and pets when exiting weedy territory.
• Join the California Invasive Plant Council (www.cal-ipc.org).
• If you have horses, use weed-free hay and feed.
• Stage an event for California Invasive Weeds Awareness Week, July 18-24.