Wildfires spark burn recovery study at 9 UC Natural Reserves

burn recovery study
Vegetation has already begun to resprout in burned areas of Hastings Natural History Reservation. Image: Jen Hunter

By Kathleen Wong, UC Natural Reserve System

August wildfires incinerated tens of thousands of acres across seven UC Natural Reserves and affected parkland adjacent to two more reserves. This fall, the UC Natural Reserve System (NRS) will deploy rapid response teams to characterize the extent and intensity of the burns, as well as the effects of wildfire on a wide range of California ecosystems.

“Although the burns are tragic in many ways, they present an unparalleled opportunity to understand how California’s ecosystems recover from wildfire,” says Peggy Fiedler, executive director of the UC Natural Reserve System. “Our teams will gather baseline information that can guide recovery efforts on our reserves and across the West.”

The burn recovery study will analyze a variety of factors affecting how vegetation, soils, wildlife fare after fire. These include how natural features such as the types of vegetation, insects, and small mammals have changed; how water quantity and quality was affected; and whether blistering temperatures have altered the ability of soils to absorb water and support plant life. The study will also analyze how the burns have altered the amount of wildfire fuels remaining on the landscape.

burn recovery study
As part of the post-burn analysis effort, CHI coordinator Becca Fenwick collected drone images of a 200-acre section of Hastings that included both burned and unburned areas. The reserve headquarters, located near the Lower Barn area, did not burn. Drone data can provide insights about the landscape that are difficult to gather any other way, such as detailed visual spectrum images (left); hill shade elevations (center); and surface elevations (more ground was uncovered by the fire when plants burned; patterned bumps are vegetation such as trees.) Image: Becca Fenwick

Comprehensive surveys

Scientists will collect information about field conditions both on the ground and from the air using drones, and compare the data against satellite imagery of each region. The team hopes to repeat these surveys to capture seasonal changes and ecological recovery. Future researchers will be able to use the information to understand how different ecosystems recover from flames that move across that landscape at different rates and intensities.

Many of the areas burned are extremely rugged. The capacity to fly drones across hazards such as ravines, cliffs, thick brush, and poison oak will enable the scientists to obtain more comprehensive surveys of areas charred by fire.

“The intensity and frequency of wildfires is skyrocketing with climate change. That means these assessments will be relevant to an ever increasing number of scientists, parks, and land management agencies,” says Becca Fenwick, program director of the California Heartbeat Initiative.

burn recovery study
The River Fire burned roughly a third of Hastings Natural History Reservation in late August. The perimeter of the reserve is outlined in blue. CHI postdoctoral fellow Yinan He combined several difference reflectance band images obtained via satellite (far left and center images) to generate burn severity data for the fire. Image: courtesy Yinan He

Growing the California Heartbeat Initiative

The burn recovery study is an expansion of the NRS’s California Heartbeat Initiative (CHI), which deploys a combination of ground sensors and aerial imagery to monitor the effects of climate change on state ecosystems. The post-fire surveys are being funded by a $150,000 grant from the Gordon and Betty Moore Foundation, which supports CHI. The grant will cover costs for teams to conduct a at least one round of surveys this fall. The NRS seeks additional funding for follow-up surveys.

The NRS reserves scorched this August were Blue Oak Ranch Reserve, Landels-Hill Big Creek Reserve, Hastings Natural History Reservation, McLaughlin Natural Reserve, Quail Ridge Reserve, and Stebbins Cold Canyon Reserve. Together, these reserves encompass some 20,000 acres. Roughly a month later, the Oasis de los Osos, a satellite of the James San Jacinto Mountains Reserve, burned when a vehicle on a nearby road ignited the Snow Fire in the Coachella Valley. Together, these fires have burned more than 16,500 acres of NRS lands.

Point Reyes National Seashore, home to Point Reyes Field Station, and Año Nuevo State Park, which encompasses Año Nuevo Island Reserve, were also scarred by fire in August. Although Point Reyes Field Station survived, about 4,700 acres of Point Reyes National Seashore burned.

“Each reserve has a long history of intensive scientific study. The fact that we can compare information gathered before and after the fires makes these data particularly valuable going into an increasingly fire-prone future,” Fiedler says.

Data gathered by the project will be made freely available to researchers at UC and beyond.

burn recovery study
A drone image of Hastings shows gray stippling in areas that suffered high intensity burns, while lower temperature grass fires appear a sooty black. These images indicate chaparral generally burned at higher temperatures than grasslands. Image: Becca Fenwick

First survey at Hastings

In early October, the CHI team kicked off its post-wildfire study with a drone survey of Hastings Natural History Reservation. Hastings is one of nine reserves that the team and its partners will sample over the next two months. The flights demonstrate how useful the post-fire surveys will be.

Wildfire burned about 600 acres, or a quarter of the Carmel Valley reserve. Drone images reveal a landscape dramatically altered by flame.

Large swaths of former grassland appear a uniform, sooty black, indicating they burned at relatively low temperatures. Sections of former chamise chaparral burned much hotter, appearing as stippled areas of white that suffered high intensity burns. Gray areas burned at somewhat lower temperatures.

burn recovery study
Burn severity information generated from relatively low-resolution satellite images layered atop the higher resolution drone image of Hastings. Both the satellite and the drone images show green tree canopies as unburned areas. However, ground surveys indicate fires did burn grasses beneath some of these trees. Image: Yinan He (burn severity map), Becca Fenwick (drone image).

Oak halos

Most curious of all, the green canopies of surviving oaks sport halos of unburned golden grass. These rings are evidence of a slow-moving fire not driven by high winds. “The additional moisture from fog drip under the tree was enough to spare the grass from burning,” Fenwick says. “This also keeps the fire from climbing into the tree’s canopy, which has the potential to kill or severely damage the plant’s photosynthetic system.”

CHI postdoctoral fellow Yinan He has compared the drone imagery with a burn analysis based on lower resolution satellite images. Overlaid, the images suggest drones and satellites excel at estimating burn severity in open areas, but that their data become problematic for interpreting the effects of fire among trees.

“What the they’re seeing from the top of a 120-foot tree tells us nothing about the ground underneath the tree canopy,” Fenwick says.

Since these eyes in the sky can’t see beneath the green tops of unburned tree canopies, their data indicates such areas are completely unburned. Surveys conducted on foot, however, often tell a different story. Areas beneath trees are frequently just as singed as the open grassland around them.

“You can imagine an area mapped as low severity because the tree canopies look fine, but there are actually moderate to severe burns underneath,” Fenwick says.

burn recovery study
A close up of chaparral areas burned by the River Fire at Hastings Natural History Reservation. Image: Becca Fenwick

Burn data discrepancies

These differences suggest burn estimates based on remote sensing data can seriously underestimate post-wildfire hazards. Government agencies and land managers use burn information to forecast the risk of mudslides and floods after wildfires. Fires can clear slopes of vegetation that hold soil in place. To make matters worse, soils that experience intense heat may become hydrophobic. Water sheets off hydrophobic soils like an omelet sliding off a Teflon pan. In a deluge, these soils can trigger debris flows like the one that buried the town of Montecito in 2018 after a major wildfire.

Burn intensity information is also used to protect water quality. “If a lot of water runs off from an area where buildings and cars have burned, that water may cause potentially hazardous chemicals to enter stream systems or catchments for drinking water systems. If managers are unaware of severe burns upstream, they won’t be expecting these inputs and won’t know to manage for them,” Fenwick says.

burn analysis
CHI coordinator Becca Fenwick conducting a post-fire drone flyover of Blue Oak Ranch Reserve. Image: Becca Fenwick

Ground game

Ground survey teams will soon compare areas that burned with similar unburned plots. Plots will examine three types of habitat: grassland, each reserve’s dominant shrub type, and a vegetation type specific to the given reserve, whether redwood forest or blue oak woodland or serpentine grassland. In each plot, teams will count and identify all plant species, the characteristics of the soils, and the occurrence of small mammals using a combination of live traps and trace DNA (eDNA) analysis.

The plots established for the study can be used as a teaching tool for future classes. Students can both further the research and practice field skills by comparing the colonization of invasive plants; soil stability and behavior; and array of insects and small mammals on burned versus unburned plots.

While some burned habitats are expected to rebound completely, others may reach a new steady state, Fenwick says. She points to shifts in the Sierra foothills, which have suffered massive fires over the past decades. “Many of lands that burned appear to have shifted from pine-dominated forest to shrub and chaparral. Grey and ponderosa pines didn’t recover because many were already dead or stressed from drought, and water resources haven’t returned due to drought. What has grown back is better adapted to the relative scarcity of water available now.”

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