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ALEX CHADWICK, host:

This is Day to Day. I'm Alex Chadwick.

MADELEINE BRAND, host:

I'm Madeleine Brand.

In a few minutes, Hillary Clinton, take note how Argentina's former first lady and now president has handled her first 100 days in office.

CHADWICK: First, the great spring rains brought a carpet of green to southern California hillsides burnt by last fall's huge wildfires. But ecologists say this lush new growth actually is not a good thing.

BRAND: In fact they are calling it a warning sign that the Golden State will face some more big fires. NPR's Ina Jaffe reports.

INA JAFFE: Orange County, south of LA is known for its endless suburban developments, shopping malls and Disneyland. But there are also tens of thousands of acres of wildlands just 20 miles from the coast. A big chunk's managed by the non-profit Irvine Ranch Conservancy. David Olson is the director of science. He stops a pickup truck on a windy ridge in an area that burned last fall in the fierce Santiago fire. It's now a brilliant green, but Olson doesn't see the beauty.

Dr. DAVID OLSON (Director of Science, Irvine Ranch Conservancy): When we look at that, we say those areas are highly dominated by non-native species that sprout very quickly.

JAFFE: Field biologist Jutta Berger, also with the Conservancy, explains it this way.

Dr. JUTTA BERGER (Field Biologist, Irvine Ranch Conservancy): Many of the non-natives can geminate more quickly than the natives and for that reason they have an edge when the first rains come.

JAFFE: These non-native plants were introduced here hundreds of years ago accidentally by Spanish colonists. The native plants squeezed out are a mix of fire-tolerant grasses, deeply-rooted shrubs and even some cactus. It's an ecosystem called California Sage Scrub. Olson said scientists used to think it was adapted to fire. Their thinking now is, well, sort of.

Dr. OLSON: We estimate that these ecosystems in their natural conditions probably burned in the range from 60 to 100 years.

JAFFE: Because the fires used to be caused mostly by lighting and in the scrub-dominated areas it isn't that common. Now with development bumping up against wildlands, fires are almost always caused by people, cigarette butts, sparks from vehicles or machinery and sometimes arson. As a result...

Dr. OLSON: Right now we are seeing fire return intervals of about five to 15 years across large areas of the natural landscape in southern California.

JAFFE: And when non-native plants take over, it only makes the fire situation worse, says Jon Keeley who studies wildfires for the United States Geological Service. The problem, he says, is that the non-natives, what he calls annual grasses, dry out faster than the shrubs, so they're more likely to ignite.

Professor JON KEELEY (Ecology and Evolutionary Biology, UCLA; United States Geological Service): Shrublands are probably more susceptible to fire for - in an average year, half the year, whereas the annual grasses make the fire season 12 months. All it takes is a few days without rain and most annual grasses will carry a fire.

JAFFE: Especially if it's driven by the Santa Ana winds that come howling out of the east on a regular basis. These winds have gusts of 50, 60 or even 100 miles an hour. And, says Keeley...

Prof. KEELEY: It is not uncommon for a Santa Ana wind-driven fire to spread 10,000 or 20,000 acres in one hour.

Unidentified Man # 1: The majority of these plants are introduced species.

JAFFE: This grass we are plotting through?

Unidentified Man # 1: That's right.

JAFFE: We trekked through weeds to get to a place that looks, to the biologist's eyes pretty much the way it should. It burned here too, but the fire blackened oak trees now rise about a field low leafy plants, some lacy knee-high shrubs and on a small hill, an explosion of wildflowers.

Dr. BERGER: There are tens to hundreds of wild flowers in these areas and each slope is different. It has its own particular sweet.

JAFFE: But even in this spot, non-native species are gaining a foothold.

Dr. BERGER: Oh, I just pulled out a black mustard that was growing in this grassland shrub mix because maybe that will make a little bit of difference?

JAFFE: Mustard is common in California. Right now its yellow blossoms decorate fields and hillsides up and down the state. But, Olson and Burger say, like the rest of the invaders, it's not much use to the animals that survived the fire.

Dr. OLSON: They don't find good food or forage within the non-native habitats. They often don't find places to build their homes or their nests as well.

Dr. BERGER: So, what you have is the direct loss of habitat. You also have direct matality after the fire, so it's a multi-prong problem.

JAFFE: Without restoration, it's a problem that's not likely to improve as people continue to move closer to wildlands and the California fire season grows longer. Ina Jaffe, NPR News.

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