The Root Race : Invasive Plants Are Outpacing Native Species on Charred Laguna Hillsides

On the once-charred slopes of Emerald Canyon, a hard-fought contest is pitting California native plants against a gangly South American interloper that can grow up to 10 feet in a single season and is moving from hillside to hillside with amazing speed.

The invader is called tree tobacco--a non-smokable distant cousin to common tobacco--and it is rising phoenix-like, its lettuce-green leaves instilling new life in land left black and barren by the 1993 wildfires.

But such greening is no cause for rejoicing among biologists keeping close watch over the recovering landscape.

Although native plants are coming back, the tree tobacco is sprouting even faster, digging its roots deep into ground that once nurtured cactus and competing with other plants for water, food and breathing room.

Brought to the region from South America hundreds of years ago by the Spaniards, tree tobacco commonly sprouts in fire-scarred and other disturbed areas. The open space of the burned acres and the nutrients in the soil have allowed the plant to prosper.

For biologists, the fire-seared hills above Laguna Beach are a gigantic laboratory, a rare chance to watch hundreds of acres of native Southern California wildlife renew itself.

So the hills’ caretakers find themselves doing battle with the hardy plant--uprooting it, cutting it, even painting its stumps with herbicide--to give bona fide California sage and cactus the chance to return.

Like so many laboratory studies, the one under way in the San Joaquin Hills is producing some surprises: the triumphant growth of tree tobacco, the slow return of cactus and the lingering question of what happened to dozens of rare songbirds that apparently scattered as the flames approached.

Scientists remain confident that the landscape will renew itself, although they say that as many as 20 years may pass before the vegetation is as abundant as before.

The rebirth takes on special urgency because the fire swept through one of Orange County’s largest and most important remaining expanses of coastal sage scrub, a distinctive mix of California sagebrush, buckwheat, cactus and dozens of other plants that once carpeted low-lying hills throughout the coastal region.

“It’s a very species-rich community, and it’s a very threatened community,” said Robin Wills, a Nature Conservancy ecologist and fire expert who is studying the Laguna hills.

Today, with 75% to 90% of coastal sage scrub lost to development, the rebirth of the Laguna burn area is considered a key part of maintaining Orange County’s native plants, animals and open space.

So several teams of scientists are monitoring these hills, including the Nature Conservancy, a research program called the Superpark Project and consultants for the county’s toll road builders.

Flames destroyed nearly 14,000 acres of sage scrub and other natural vegetation in the San Joaquin Hills, leaving behind ashen hillsides, singed oaks and the carcasses of cactus.

“This was a black, empty landscape,” Wills said as he drove along a dirt road through Emerald Canyon. “I remember driving down here the day of the burn. All of Emerald Canyon was just trashed. Black.”

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Today, few outright reminders of the fire are visible from atop Emerald Canyon, with its breathtaking view of brush-spotted slopes plunging toward the Pacific Ocean.

Signs of rebirth are visible everywhere--new-grown California sage brush, red-tinged deer weed, even pale green miniature cactuses sprouting from charred ones.

Scientists point to the new growth as proof of how fire can reinvigorate old habitat, increasing diversity.

“All of a sudden, there’s an abundance of light, there’s an abundance of water, of growing space, of nutrients,” Wills said. “It gives everything an opportunity to grow.”

But one of biologists’ biggest concerns is that the light and nutrients unleashed by the fire could lead to a burst of growth by non-native plants such as tree tobacco, artichoke thistle and non-native grasses. That could slow the return of native plants and animals.

In fact, one riddle still puzzling scientists is the ultimate fate of two rare birds--the California gnatcatcher and the cactus wren--that live in coastal sage scrub.

The gnatcatcher is the tiny songbird that triggered a regional tug of war between developers and environmentalists in the early 1990s. It is listed as threatened under the federal Endangered Species Act.

The Laguna fire area was once home to hundreds of these birds--127 pairs of gnatcatchers and 282 pairs of cactus wrens, according to one published study.

Those numbers dropped precipitously after the fire, with only 12 gnatcatcher pairs found in the spring of 1994, and five pairs a year later. A new study shows the numbers climbing to 11 pairs this year.

Experts believe that few of the birds were killed by the fire, but that they fled to surrounding areas, where their numbers were found to rise noticeably in 1994. But the 1995 winter rains and cold may have further thinned their ranks.

The cactus wrens’ future is intrinsically tied to the return of cactus, which takes longer to grow than shrubs and grass.

That in turn heightens concern about the post-fire surge of tree tobacco, which seems to flourish in spots where cactus once grew.

Still, each month, clues emerge that life is returning to normal.

More deer and coyotes have been spotted in the reserve area, said Trish Smith of the Nature Conservancy.

And this year, the surviving oak trees produced their first major crop of acorns since the fire.