Sudden oak death study aids reserve, teaches field research
It’s a late November morning in Big Sur, and four UC Santa Barbara students are pushing through the forest on the steep western slopes of the Santa Lucia range. The fog that still shrouds the coastal highway is just a memory here, and the late winter sun shines strong through the lattice of overhead foliage.
Mark Readdie, director of Landels-Hill Big Creek Reserve, leads the students past dense stands of madrone, bay laurel, and coast live oak. Dry leaves crunch underfoot with every step.
The group pauses often to take compass bearings, unspool measuring tape, and apply standard forestry techniques to characterize the trees along this steep slope.
“Canopy position?” calls Derek Stanley-Howarth, holding the clipboard. Stanley-Howarth and his four classmates are all taking Ecology and Management of California Wildlands at UCSB this quarter. Their instructor, ecologist Nicole Molinari, has brought the students on a three-day expedition to learn about this ecosystem while acquiring field study skills.
Student Hailey Allison cranes her neck upward to assess the reach of this coast live oak’s branches. “Dominant,” she answers.
“Health?” Stanley-Howarth asks. The tree’s branches are dense with glossy leaves. “Healthy,” Allison responds.
Then Sarah Russ points out an orange spot on the tree’s gray-brown bark. “Is that a canker?” she asks.
The spot resembles a knife gash. The bark surrounding the rust-red gape is stained by ooze from the wound.
Nodding grimly, Readdie produces a knife to collect a sample of the canker for later analysis.
Notorious plant killers
Cankers like this one are a telltale symptom of sudden oak death, or SOD. Since its introduction to the West Coast via nursery plants in the mid 1990s, the disease has killed millions of native trees from southern Oregon to Big Sur.
The disease agent responsible is Phytophthora ramorum, a member of a group of microscopic, filamentous, fungus-like organisms called oomycetes. Oomycetes include many notorious plant pathogens, among them the agent behind the Irish potato famine of the mid-1800s.
While P. ramorum won’t cause mass human deaths, it is devastating coastal California’s native forests. The disease fells ancient landmark trees, leaves glaring brown holes in otherwise green forest canopies, and ratchets up the risk of catastrophic wildfires.
Sacrificing bays to save oaks
At Landels-Hill Big Creek Reserve, ecologist Kerri Frangioso is testing a method to manage SOD and minimize true oak casualties. The reserve is part of the UC Natural Reserve System, a network of 39 California wildlands managed for research and education.
“Our biggest and best tool at this moment is to keep SOD’s bay laurel and tanoak hosts away from true oaks,” says Frangioso, citing observations by the USDA Forest Service. Frangioso works with UC Davis plant pathologist David Rizzo, who first described the pathogen responsible for SOD and continues to research the disease.
Abundant in mixed evergreen forest, bays and tanoaks appear to be the Typhoid Marys of sudden oak death. They often populate the understory beneath larger true oaks, and spread the infection readily to trees within a 30-foot radius.
At Big Creek Reserve, Frangioso can manipulate the composition of the forest to determine whether a new control method can in fact protect oaks.
She and reserve director Readdie have set up two hectare-sized plots dominated by true oaks but with a few bay laurels in the understory. All the bays will be removed from one plot, but left alone in the other. Over the next five to ten years, they hope to discern a difference in true oak survival.
“I’m charged with providing a pristine environment at the reserve for research, teaching, and conservation’s sake. I don’t want to lose these live oaks, to have them die on my watch,” Readdie says.
Learning and research for classes to come
At the same time, the study will let visiting students lend a hand with a study critical to California ecosystem health.
“I wanted to save these oaks. Nicole applied to bring her class. I thought, wait, this is a wildland management class; we’ll have 25 students all learning about management, so let’s enlist them,” Readdie says. “We’ll look for other classes to follow up with monitoring.”
Frangioso delayed her project slightly to coordinate with the arrival of the class. “I had been pressuring Mark for awhile, saying Big Creek should do SOD management. But he wanted to ensure it would not be just another experiment but a learning and teaching opportunity. Classes could learn field techniques, forest ecology and management, and all the while collect valuable data for Big Creek in the future.”
Despite having to clamber up and down steep slopes while dodging poison oak and dense foliage, her student volunteers are enthusiastic. “This work is more interesting than other labs we’ve had because what we’re doing is applicable to a problem that hasn’t been solved,” says Shannon Malone.
“I’m really happy to be here. It gives me a chance to try out techniques and participate in this research project, talk to experts and land managers,” says Sarah Russ.
Ratcheting up fire risk
Researcher Frangioso is not only interested in learning more about SOD, but has a personal stake in preserving local forests. She’s a resident of Big Sur as well as a volunteer firefighter.
“It’s not just the loss of trees, which is horrible enough, but the aftereffects of downed trees,” Frangioso says. “SOD is decreasing our ability to handle fires.”
The exotic pathogen is even harming coast redwoods, a species impervious to most forest afflictions. “Redwoods are typically resistant to both SOD and fire, but when facing both together are not as able to survive,” Frangioso says. In fact, Frangioso and colleagues have found that medium-sized redwoods (20-50 cm in diameter) in areas hit by the disease are twice as likely to die after fires.
Fires in disease-afflicted areas last longer and burn hotter than typical blazes. The dry, dead hulks of the largest SOD-killed trees can burn white-hot for many hours or days. “It’s difficult to put those fires out, and logs can blow embers into new areas to start another fire,” Frangioso says. “If you keep an open understory forest, you’re reducing the risk of catastrophic, more intense fire but also reducing the potential to harbor the disease,” Frangioso says.
The intense, persistent heat from big log fires can also damage the shallow root systems of trees like redwoods, as well as sterilize seeds lying dormant in the soil. Forests then require an unusually long time to regenerate.
Little can be done at present to protect trees in Big Creek’s moist, shady canyon bottoms from SOD. But the reserve’s upper slopes are clad in mixed evergreen forest, which also covers a goodly part of central California. The hope is that within these widespread bay-tanoak-live oak woodlands, people may be able to keep this exotic disease out and the state’s heritage oaks healthy.