Wild Enemies

'We try to get the worst first...we've got a fair shopping list of plants," says Jim Harrison, river committee coordinator for the San Diego Audubon Society. "We hope that, over time, we'll be able to put the river back into some semblance of what it used to look like naturally versus a collection of junk and so forth running down through the valley and great huge masses of plants from South America all over the place." As an affiliated member of the San Diego River Coalition, the Audubon Society has adopted the segment of the river that runs west of Interstate 5 to the mouth of the river along the south edge of Mission Bay Park. For the second annual San Diego River Day Celebration on Saturday, May 21, the Audubon Society is hosting a cleanup. "[The coalition groups] will all be out there observing the day in some way. We chose to move our cleanup day in order to coincide with the river celebration," says Harrison. Typically, the Audubon Society hosts a cleanup for its segment every other month.

"We're at the bottom of the river," says Harrison. "Anything that washes downstream gets deposited along our banks." Volunteers are asked to collect refuse. "We're talking about paper scraps, abandoned clothing, and a lot of cans. We've found old bicycles and mattresses. Our segment does not have any regular [transients]. Occasionally some people will try to set up there, but it's not the same quality as the next area upstream. It's pretty visible."

Trash is only part of the problem. Invasive plants along the river's edge threaten indigenous species. "Any plant growing out of its ordinary area that doesn't have any natural enemies can just run wild. That puts the plant on our priority list. If they're here and they prosper here, they do so at the expense of our native plants that already have enemies, but then have to take on the added burden of these [invaders]."

There are six plants that volunteers are instructed to look for and remove. Harrison says he has "almost always had to deal with the Russian thistle, or tumbleweed...it has ferocious thorns on it, it's not edible for the wildlife in the area, and it's harmful to the people who walk around and get scratched up by it."

Another pest is the castor bean plant. Though humans have used its oil for centuries, the plant itself is poisonous. It's scientific name, Ricinus communis, is Latin for "common tick." Swedish naturalist Carolus Linnaeus, who named it, thought the plant's seeds resembled large, blood-engorged ticks -- an image that should deter most people from experimenting with the poisonous seed's taste.

Ice plant is one of the most dangerous, for even if it dies, its salt deposits leave the area uninhabitable. "This is an imported plant from a different environment entirely. I'm not aware of any animal that uses it for food, and it has the ability to suppress the plants around it. Once a patch of ice plant is in place, nothing else can grow there; it uses the resources and takes over the land, and native plants just can't survive against it." Harrison's back yard was covered in ice plant for many years before he removed it almost a decade ago.

Of the Brazilian pepper tree, Harrison says, "It has no merit other than it's green." This tree is a rapid-growing, nutrient-sucking detriment to native plants. The Brazilian pepper tree and the tree tobacco plant (an invasive easy to spot because of its bright yellow, tubelike flowers) were originally brought to San Diego for their ornamental value.

Pampas grass is one invasive plant "so prolific and ferocious, there have been some attempts to try and get it put on a blacklist," meaning it would be illegal to possess or plant it locally. "It forms great, huge stalks with a seed head up on top." Each stalk produces millions of seeds that require no pollination in order to develop. "The problem is that once they get more mature, they form a dry bed [that creates] a fire hazard. If someone walks by and throws a cigarette, there will be a brush fire."

"This is a loser of a year," says Jim Peugh, coastal-wetlands conservation committee chair for the San Diego Audubon Society. "Other years we make a lot of progress, but this is very much a defensive year because of the rain." At the last cleanup, volunteers filled around 40 large plastic bags with invasive plants and a dozen with refuse. -- Barbarella

San Diego River Day Celebration and Cleanup Saturday, May 21 9 a.m. to noon San Diego River, west of I-5 to the river mouth along the south edge of Mission Bay Park Info: 619-682-7200 or www.sandiegoriver.org