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Monday, Nov. 5, 2007 | As scientists throughout the region begin surveying wildfire damage, they say they are concerned about one fact: A large swath of land that burned in 2003 went up in flames again in the late October firestorm.
The fires rushed through approximately 145 square miles that burned in 2003, according to a San Diego County estimate. That’s equal to the size of Oceanside and Camp Pendleton combined.
The overlapping flames increase the possibility that native plants will be replaced with invasive weeds, which provide fewer habitats for animals and increase fire risk. If that happens, it will exacerbate a problem that has already affected huge portions of San Diego County’s landscape. Jon Keeley, a U.S. Geological Survey research ecologist, said he estimates that over time 25 percent of San Diego County’s natural plant life has been lost to invasive weeds.
The repeat fire can damage native plants that aren’t accustomed to such high-frequency fire. The native vegetation that blankets the region’s hillsides has adapted to infrequent fires that hit once or twice a century. Occasional fires allow enough time for plants to regenerate and create new seeds that they then drop when the next fire hits.
But across large swaths of San Diego County, fire returned before many native plants recovered from the 2003 Cedar, Paradise and Otay fires.
“We have a potential major ecological disaster we’re looking at here,” Keeley said. “Potentially we could have lost tens of thousands of acres of native vegetation to this event.”
In chaparral, the term that describes the major plant community found throughout the region, plants regenerate in two ways. Plants such as California lilac grow from seeds. Plants such as chamise sprout from their root systems.
The repeat fires will have a sharper effect on plants that sprout from seeds, Keeley said. After being hit by fire, some need 10 years before they can regenerate, create new seeds and safely burn again. While plants that sprout from their root systems will have their populations thinned out, Keeley said seed-sprouting plants could be instantly wiped from large swaths of the landscape.
“They are toast,” said Janet Franklin, a San Diego State biology professor, “because they don’t mature in four years.”
If the land was left undisturbed, Franklin said, the root-sprouters would recover first and the seed-sprouters over time would return to the plant community. But even the root-sprouters may struggle, because they’ve had so little time to recover from the 2003 fires.
And even that is the perfect vision for how nature would recover.
Invasive weeds complicate the recovery. The repeat fires give a boost to weeds, the kind of grasses that turn hillsides blonde in late summer.
Invasive grass first arrived in San Diego County sometime around the 16th century, Keeley said, likely tangled in the fur of sheep that the first explorers brought.
The ensuing grass invasion is a problem throughout the Southwest. In Arizona’s Sonoran Desert, scientists worry that introduced grass is causing too-frequent fires in a landscape that never burned before. The saguaro cactus, which has not adapted to fire, is suffering as a result.
Here’s the problem with invasive grasses: As they spread, they increases the likelihood of fires. The grasses sprout each year, drop seeds and dry out by summer. If fire sweeps through, the grasses will return the next year — leaving the landscape ready to burn, making native plant recovery more difficult.
It’s a self-fulfilling prophecy. More fire brings more grass, and more grass causes more fire. While native plant communities can take several years to grow back, grasses can rebound within a year.
If native plants struggle to rebound, “there’s a lot more bare ground,” Franklin said, “and that’s more opportunity for grasses to invade and inhibit the reestablishment.”
Some are optimistic that the plant communities affected by both the 2003 and 2007 fires will recover. Tom Oberbauer, chief of the county’s Multiple Species Planning Division, said fast-moving and low-intensity flames passed through many already-burned areas.
“I have a lot of faith in the recoverability of the vegetation we have here,” Oberbauer said.
Oberbauer said he is concerned, though, about the Harris Fire this year and 2003 Otay Fire. The two overlapped on about 25,000 acres, including land near Otay Mountain that has been set aside for habitat preservation.
While the Harris Fire burned part of Otay Mountain, the flames appear to have dodged populations of Tecate cypress. The mountain is home to the largest remaining population of the cypress, which is home to the rare Thorne’s hairstreak butterfly.
David Hogan, conservation manager of the Center for Biological Diversity, an environmental group that has unsuccessfully petitioned to have both species listed as federally endangered, said the Harris Fire’s path on Otay Mountain was “a very, very close call for a species that could go totally extinct in just one more fire.”
Biologists caution that the fires’ full effect may not be known for some time. While fire leaves the landscape looking charred and black, plants can bounce back quickly. In Cuyamaca Rancho State Park, where all but 500 of the park’s 26,000 acres burned in 2003, springtime brings a prolific explosion of white lilac blossoms amid the blackened tree snags.
But concerns still linger about the regrowth of the park’s trademark conifers, said Mike Wells, superintendent of California State Parks’ Colorado Desert District. Very few survived the fire. Of 800 pines in one survey area Wells monitored, just three trees remained after the Cedar Fire.
While some seedlings are now sprouting, said Franklin, the SDSU professor, “it could still be a very long time before it would look like the forest we all loved.”