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Monday, December 10 , 2018, 1:15 pm | Mostly Cloudy 63º

 
 
 
 

Los Padres National Forest Won’t Seed Areas Burned in Thomas Fire

Slow vegetation regrowth is reported on South Coast hills, with concern that there will be a similar risk of post-fire debris flows next winter

 

More than half of the Thomas Fire burn area is Los Padres National Forest land, and the U.S. Forest Service has not and is not planning to seed or hydromulch, said Kevin Cooper, BAER team leader.

Burned Area Emergency Response reports are developed within a week of wildfire containment to analyze impacts, including an increased risk of erosion, sedimentation, flooding and debris flows.

Losing vegetation in the fire causes more erosion, and heavy rainfall can cause post-fire debris flows and flooding, as it did in the deadly Jan. 9 Montecito debris flow. 

During an update on the condition of local watersheds after the fire and debris flow, Cooper told the Santa Barbara County Board of Supervisors that the burn area is experiencing very slow vegetation regrowth, including the coastal slopes on the South Coast. 

They would expect to see 50 to 60 percent ground cover by now, he said, but there was 5 to 10 percent cover as of April, as growth is hampered by dry soils and below-average rainfall.

Cooper said no slope treatments — seeding or hydromulching — would be effective in these conditions, with steep hills and dry soils.

“Normally the issue with regrowth is not the native seed; there is plenty of seed up there now,” he said. “The chokepoint, or the limiting factor here, is the soil moisture.”

Teams have observed stump sprouting and vegetation “in stasis,” waiting for moisture, he added.

“One other thing about that, when we put vegetation in there, when we plant, it is usually lighter grasses and plants that grow quickly to give us good cover, that also provides a very fine fuel bed — one of the worst things we could see is another reburn in this area, we don’t want to have that happen.”

Planted vegetation also can out-compete native plants, he said. 

The Los Padres National Forest team will give the county an updated report on vegetation growth in the summer.

debris flow hazard map Click to view larger
A U.S. Forest Service and U.S. Geological Survey debris flow hazard map developed between the Thomas Fire and the Jan. 9 Montecito debris flow.  (BAER photo)

“I don’t think it’s going to change much based on the soil moisture that’s out there,” Cooper said.

The 281,893-acre Thomas Fire scorched public and private land in Santa Barbara and Ventura counties with varying degrees of soil burn severity, which impacts how fast plants grow back and the risk of post-fire debris flows.

Soil burn severity is all about how much heat was delivered to the soil, Cooper said, adding that it is the basis for debris flow hazard maps and other risk assessments. 

“Grassland fires and shrub-land fires can remove all the vegetation on the surface but not cook the soil too deeply, which is a good thing, but if it is burned very deeply, we get more erosion and issues that way,” he said.

The BAER team and WERT — the CalFire Watershed Emergency Response Team — used the same soil burn severity map for their assessments, including the debris flow potential hazard map developed Jan. 3, just six days before the deadly Montecito debris flow.

Representatives from both groups told the county that it looks as if there will be a similar risk of post-fire debris flows next winter. There is still a lot of material in the burned hills that could come down in a flash flood or debris flow, they said.

Kevin Cooper Click to view larger
Los Padres National Forest BAER lead Kevin Cooper speaks at a community meeting May 1 in Santa Barbara.  (Brooke Holland / Noozhawk photo)

Soil burn severity was moderate for 65 percent of the Thomas Fire area and low for 23 percent of areas because of high pre-fire ground cover, according to the BAER report.

“In most of the moderate burn severity, and some of the high burn severity (particularly on south-facing slopes), there is very little vegetation or ground cover remaining except surface rock,” the BAER report stated.

“Within the Thomas Fire burned area, slope failures such as rock fall, debris slides, debris flows, dry ravel, surface erosion and gullying have shaped the landscape in the past. Those processes will now be exacerbated, relative to the degree of fire burn severity, and the intensity, frequency and duration of future storms.”

County supervisors asked if there were any post-fire treatments that could provide erosion control, and Cooper said the Los Padres National Forest is not recommending seeding or hydromulching Thomas Fire-burned areas.  

“It’s hard to hear this I think, unfortunately, but in these cases we have to wait for mother nature to take its course and beyond that it’s moving people out of harm’s way. Of course, that’s another kind of treatment. But I don’t believe there’s a slope treatment that would be effective under these conditions.”

burned hills Click to view larger
Slopes burned in the Thomas Fire had very little vegetation growth in April, according to the Los Padres National Forest BAER team.  (BAER photo)

The Forest Service makes post-fire seeding decisions on a case by case basis, Cooper said. The agency used to do it frequently, in the 1980s and 1990s, but research found that planted vegetation did not help erosion control any better than natural growth in the Central Coast area, he said.

Post-fire treatments identified in the BAER report mostly include trail, road and campground closure/warning signs, and installing some culverts. 

Cooper said the Forest Service has used hydromulching for soil retention, but the method works only on moderate slopes for moderate rains, and most South County hills are too steep.

“The kinds of rains that produce a debris flow are the same rains that would take out hydromulching,” he added.

It has been used in some areas burned in the Gap Fire and Jesusita Fire, he noted.

In the case of the Jesusita Fire burn area, Los Padres National Forest used aircraft to drop the mulch on a 200-acre area, which was determined to be “the most effective method to minimize erosion across the burned slopes and help the watershed recover.” ​

The post-Thomas Fire vegetation recovery is stronger for the north slopes of the Whittier Fire and Sherpa Fire, on the slopes near Lake Cachuma and Highway 154, according to the BAER report.  

There is 20 to 50 percent ground cover and some reduced risk of flooding in that area, though the south, coastal slopes of the burn areas have had less regrowth, Cooper said.

Growth along Highway 154 will reduce sedimentation for Lake Cachuma, said Rob Lewin, director of the Office of Emergency Management.

The BAER report can be viewed online here and the WERT report can be viewed online here. They also are linked from the county's emergency information page.

The Federal Emergency Management Agency's new flood hazard maps are expected to be released in mid-June, officials said at a recent community meeting. 

In Montecito, the Romero Canyon, San Ysidro Canyon, Hot Spring Canyon and Cold Spring Canyon drainages are the largest and “present the most widespread hazards due to the large number of residential structures located downstream and at the mouths of tributary canyons,” the WERT report states. “Additionally, numerous structures are located within the FEMA 100-year and/or DWR Awareness Floodplain in this area.”

The report also notes: “The southernmost portion of Montecito located along the coastal strip contains low lying topography that is prone to flooding. As such, debris flows originating in channels above Montecito can flow downslope through the community and impact the low lying coastal strip as sediment and debris laden floods.”​

Noozhawk managing editor Giana Magnoli can be reached at .(JavaScript must be enabled to view this email address). Follow Noozhawk on Twitter: @noozhawk, @NoozhawkNews and @NoozhawkBiz. Connect with Noozhawk on Facebook.

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