Wildfire Woes for Things That Swim, Hop, Crawl, and Eat a Lot

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Clarice Nassif Ransom

Welcome, and thanks for listening to the USGS CoreCast. I'm Clarice Nassif Ransom. The Southern California wildfires in late 2007 impacted more than humans. Wildlife also suffered.

Today, we are joined by USGS Biologist Robert Fisher. Robert will describe what a team of USGS scientists discovered about the wildfire impact on wildlife. He'll also talk about some endangered frogs that were in need of rescue and how falling rocks might have had a profound impact on rainbow trout. Thanks for joining us, Robert.

Clarice Nassif Ransom

Tell me about how these fires affected wildlife?

Robert Fisher

These fires have both direct and indirect effects on wildlife. The direct effects are direct mortality for animals that are active during that period of time where a deer or larger wildlife that might have low mobility to get out of the fire footprint.

A lot of smaller wildlife is already underground during that time of year because it's starting to get colder starting to...their activity's reduced because there hasn't been water for a long time, so a lot of small animals, a lot of reptiles and amphibians, have minimal activities. So their direct mortality maybe lower than some of the bigger animals that are still active.

But the indirect is what's maybe going to hit those later...indirect meaning that the post-fire changes in the landscape. And that's what's really going to be important for understanding their biology and their population status over time.

Indirect factors include what happens with ash and whether the ash may be toxic, whether their food plants come back in the right ways, whether their basking sites are there for some kinds of animals, and a variety of different kinds of ways that they might be affected indirectly from the fires.

Clarice Nassif Ransom

Are there any specific species that you would like to mention directly or indirectly impacted?

Robert Fisher

We have been studying the 2003 fires, and the terrestrial habitats of post- 2003 fires, which were similar to these 2007 events. Certain groups of animals seem to be disproportionately impacted by the fires, and we are not exactly sure of the mechanisms yet.

But one group is the salamanders—the non-forest salamanders; salamanders living in the chaparral habitats and the scrubland habitats. We are not sure if whether there is a physical change in the landscape after the fires where they do not have enough mesic habitats to occur in- wet habitats for their needs—or whether there is a toxic effect of the ash that may be directly causing mortality.

The other group is shrews, and shrews have to eat a lot of food to survive. They're different than other small mammals that are mostly omnivores in our areas...not omnivores. . . they are different than other small mammals that are typically herbivores or granivores in our area. They're actually carnivores. They have high metabolism, and they need to eat a lot of foods.

It could be that either shrews are directly affected after the fires because of the lack of mesic habitats, because they usually prefer some amount of moisture, or that their food hasn't recovered—the invertebrates that they eat have not responded well to the post-fire environment and that they can't find enough food to survive.

Clarice Nassif Ransom

O.K. Thank you. And tell me about dry ravel-R-A-V-E-L-which is...I think you've described before as a river of rocks falling down a hillside. How has that impacted the rainbow trout population after this 2007 wildfire?

Robert Fisher

We very are particularly interested in this population in Orange County because it's one of the last, and maybe the last, genetically pure southern steelhead landlocked form of southern steelhead rainbow trout.

And in studying that site post burn, we saw extreme dry ravel events, which are basically a lot of inorganic or mineral material that's falling down the hillside because the organic material, the plant matter, is gone and the canyon is very steep, and the deep pools are in the steep sections of the canyon.

And so those are the places where the materials are basically filling in the water and displacing the water and creating a shallower pool that is going to have increased temperature and maybe even disappear and have no standing water because the water will be underneath all that material.

And so that is going to directly affect the ability for fish to survive, especially trout that have more cold water conditions than some of the other warm water fishes that are native to the lowlands in Southern California.

Clarice Nassif Ransom

O.K. Is there anything in particular about these rainbow trout that you found or discovered?

Robert Fisher

This trout population, we've been looking at for 20-plus years .It's one of several populations that were persisting in that part of the Santa Ana Mountains in Orange County, and it's the last population left.

The other populations have slowly blinked out due to the extreme drought conditions we've experienced as well as the big floods that took place in 1969 that filled in a lot of areas in this canyon with materials and reduced the amount of perennial water in that area.

This is a fragmented population that's isolated by several reservoirs, so it really is a tiny population of fish that are isolated in an upper headwater canyon.

When I was there in July, there seemed to be 100, maybe a little bit more than 100, fish of all different size classes scattered about a quarter of a mile of the canyon, primarily in maybe 10 to 12 big pools and then scattered in some smaller pools. So it really is a restricted area, a restricted population, and any additional stresses in that type of situation are really going to have an impact on them.

This dry ravel where the pools are actually filling up with material, there's not a lot of options for the fish. They are trapped there so they either are going to make it, survive, or not, based on that.

But the concern is that once the rains hit, and we actually have the dry ravel, the materials that are falling in the canyon now, become mobilized and really homogenize across the creek system and fill in the interstices as they erode in there. That's going to remove all or most of the rest of the perennial water sources that are in that canyon.

Clarice Nassif Ransom

Wow, OK. I hear some of our scientists rescued a frog population—maybe not this fire, but in previous, and what are the frogs doing now, and when can they go home? Tell me a little bit about that.

Robert Fisher

Yeah, we've been working with the mountain yellow-legged frog, which is an endangered species, since 2000 before it was actually listed. During that period of time, there's...it only occurs now in three of the four mountains it occurred in in Southern California, and it occurred in less than less than 15 populations, let's say, since the early 90s. Now it occurs in 8 populations.

And we've been watching the largest populations blink out for different reasons. And in 2003, the largest population at that point basically went to zero after a debris flow event following the 2003 fires. And that population and that habitat really changed.

The next biggest population now is in the mountain range south of that, and we want to use that population to help re-establish frogs in other areas. And so the drought in Southern California in the last 2 years has really limited that population in the San Jacinto Mountains to just a handful of pools and not very many animals. And so as those pools were drying up last summer, we were able to salvage tadpoles to bring into the Wild Animal Park's Center for Reproduction of Endangered Species facility to try to grow them up so that when we get water back into some of these canyons, we can try to bring those frogs back into the wildlands.

At the same time, right after we removed those frogs, the fire burned up the northern part of that mountain range, and luckily it was stopped before it got to the forest that was covering that canyon where we saved these animals.

So, that canyon is still full of a lot of dead trees, and we are concerned that it could ignite relatively easily at any point. We really are hoping to try to, in the short term at least, manage the captive population while we try to get places back in the wild that we can move animals to...so through captive breeding, produce more animals and then move them back into nearby canyons that might be suitable now because they formally had trout stocking programs that no longer exist.

Clarice Nassif Ransom:

Well, thanks again for joining us, Robert. We really appreciate it.

And thanks to all of you for listening to this episode of CoreCast. You can find out more information about the science behind wildfires at usgs.gov/hazards/wildfires.

CoreCast is a product of the US Geological Survey, Department of the Interior. Until next time, I'm Clarice Nassif Ransom.

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Music credit:

"Naughty Hula Eyes" by Any Iona

Mentioned in this segment:

• The USGS Wildfire Natural Hazards Site

• The Center for Reproduction of Endangered Species

  • mountain yellow-legged frog study

• USGS news release on the problems ash can pose to the environment