Posts Tagged: oaks
Knowing the names of trees is a point of pride for many California Naturalists. So a walk among the diversity of oaks at the Pepperwood Preserve left many feeling humbled.
The three-hour excursion was part of the UC California Naturalist Regional Rendezvous in October at the 3,200-acre nature preserve nestled in the foothills between Napa Valley and Santa Rosa.
Excursion leader Steve Barnhart, academic director emeritus at Pepperwood, said there are 500 oak species in the world; 21 in California. But cohabitating on the rolling hills and valleys of the Golden State, many oaks have produced hybrids that combine characteristics, making identification challenging.
Doctoral candidate Phrahlada Papper, who is studying oak tree genetics, said, “I'm of the mind that you shouldn't ever name an oak.”
Even the tan oak, long thought to be misnamed, is coming under new scrutiny.
“It's not an oak,” Barnhart said. “It has acorns, male and female flowers on the same stalk, but tan oaks are insect pollinated. True oaks are wind pollinated. Tan oaks are closer to chestnuts.”
But Papper raised his hand. “Genetically, it might be an oak,” he said.
Barnhart laughed. “So tan oak is up in the air. That's why it's so much fun to be in science,” he said. “I learned something today.”
In popular culture, oaks are thought to be majestic, towering trees, with wide spreading branches. However, Barnhart said, most California oaks are shrubs, including the leather oak.
Leather oaks grow in serpentine soils and have the ability to produce two types of flowers, one in the spring and another quite different in the fall. Leather oaks are monoecious, they have both male and female flowers on the same plant. On a particular leather oak at Pepperwood, Papper was surprised to find male and female flower parts in one bract and surmised that weather patterns may be responsible.
“California has weird weather and with climate change, it's getting even more weird,” Papper said.
Papper believes tracking phenology, the cyclic and seasonal changes in plants, is an ideal citizen science project for California Naturalists. One such project underway at Pepperwood is led by Wendy Herniman. A University of Edinburgh, Scotland, master's student, Heniman is documenting the phenology of 10 Pepperwood oak trees: 2 blue oaks, 3 coast live oaks, 2 black oaks and 3 Oregon oaks.
“Pepperwood is looking at climate change. It's a designated sentinel site. We're monitoring fog, we have soil probes, and we're collecting all weather and climate information. We can tie that to phenology,” she said. “We're trying to find out if phenophases are changing.”
Understanding the changing phenophases is important, Barnhart said.
“Everything is connected,” he said. “If acorns are produced early, animals species that depend on the food source will be disrupted. You have imbalances in the timing of the natural world. With climate change, what are the effects we'll be seeing?”
Results of the 2015 Sudden Oak Death Blitz survey reveal coastal mountain infestations in areas such as Big Sur (19% infection), the Santa Cruz Mountains (13% infection), and western Sonoma County (12% infection) remain high despite an overall decline in infection rates from 4.4% to 3.7% across California's 15 infested counties.
Sudden oak death (SOD) symptoms have been seen in Alameda, Contra Costa, Humboldt, Lake, Marin, Mendocino, Monterey, Napa, San Francisco, San Mateo, Santa Clara, Santa Cruz, Solano, Sonoma and Trinity counties.
“Understanding the current disease distribution is key to preventing sudden oak death spread. Citizen scientists have been an invaluable help with this task over the last decade,” said Matteo Garbelotto, UC ANR Cooperative Extension specialist in the Department of Environmental Science, Policy and Management at UC Berkeley, who organizes the annual SOD Blitz.
Several new SOD outbreaks of note were identified during the blitzes. Two infected California bay laurel trees were confirmed near UC Berkeley's West Gate, a high-traffic, high-risk area with many heritage oaks. An infected California lilac shrub was found in the Presidio of San Francisco's (part of the Golden Gate National Recreation Area) southeastern quadrant. An infected California bay laurel tree was confirmed in Danville (eastern Contra Costa County) in an area where SOD had not previously been reported, and an urban park in Saratoga was found infested for the first time.
Nineteen citizen science-based SOD Blitzes (largest number of blitzes to date) were held this spring, two of which were new this year – one in Trinity County and one on Kashia Band of Pomo Indian land in Mendocino County. The 504 volunteers surveyed nearly 10,000 trees from San Luis Obispo County, north to Mendocino and Trinity counties. Each volunteer was trained to identify Phytophthora ramorum (the plant pathogen known to cause SOD) symptoms on California bay laurel and tanoak leaves. “Blitzers” had up to three days to collect and record locations of symptomatic samples, which were then sent to the Garbelotto lab for DNA analysis to determine the presence or absence of the pathogen.
Garbelotto is sharing results from the spring blitzes as well as new recommendations for SOD management at workshops being held around the Bay Area. Workshops will be held in Sebastopol on Nov. 3, in Berkeley on Nov. 4, and in San Rafael on Nov. 13. For details, see “Community meetings” at sodblitz.org.
For landowners in infested areas concerned about protecting their oak trees, Garbelotto will reveal his updated three-step SOD management plan. He will show them how to:
- Use the SODMap mobile app to help assess risk of oak infection (see sodmapmobile.org).
- Determine if California bay laurel trees near high-value oaks should be considered for removal (using a new buffer zone new chart - http://nature.berkeley.edu/garbelottowp/?page_id=2345).
- Apply phosphonates to high-value oak and tanoak trees to boost immunity (updated dosages and application frequencies at http://nature.berkeley.edu/garbelottowp/?page_id=2348).
Infection on California bay laurel and tanoak leaves indicates arrival of P. ramorum to an area, but true oak (California black oak, coast live oak, canyon live oak and Shreve's oak) infection typically requires a couple of years with wet conditions after pathogen arrival. Therefore, preventatively treating oaks to help ward off infection is best done when early indicator species first show symptoms, prior to oak infection and optimal conditions for the pathogen – cool and moist.
These surveys are made possible thanks to funding from the USDA Forest Service and the PG&E Foundation as well as help from the California Native Plant Society.
For more information on the workshops, go to sodblitz.org or contact Katie Harrell at (510) 847-5482 or firstname.lastname@example.org. For more information on sudden oak death and P. ramorum, visit the California Oak Mortality Task Force website at suddenoakdeath.org.
Bill Tietje is a UC Cooperative Extension area natural resources specialist in the Department of Environmental Science, Policy and Management at UC Berkeley. He is based in San Luis Obispo.
Early leaf drop is a deciduous tree's adaptation for conserving water that it otherwise would lose through transpiration from its leaves, which can occur as long as the leaves are green.
More recently, another deciduous oak, the valley oak, kept its brown, dead leaves longer than usual. This could be due to the virtual lack of rainfall and wind last fall and early winter, both of which typically contribute to an earlier leaf drop.
So why are these things happening?
As you know, it's dry out there! In fact, the past 12 months have been the driest on record, going back to 1870. Not surprisingly, many oaks are under water stress—and they show it.
This situation reminds one of the conditions during the drought of 1988-1990, one of the most widespread and severe droughts in the state's history. Coincidentally during that time in three counties on the Central Coast, UC Cooperative Extension was conducting a study that included the monitoring of coast live oak, blue oak, and valley oak trees on study plots scattered throughout Monterey, San Luis Obispo and Santa Barbara counties. Many of the oaks looked stressed. Some of the trees succumbed to the drought. Small oak trees in the undergrowth and on steep terrain with southern exposure, and shallow, infertile soil, were most vulnerable. Such sites are typically drier than other slopes and orientations. However, large, mature trees—or, large branches on these trees—on more gentle slopes, also died. Usually there is not only a single factor that causes the decline and mortality of oak trees. Drought stress lowers the trees' defense, making the trees more susceptible to mortality factors such as decay fungi and boring beetles. Most likely the drought caused early death of some oak trees that would have persisted otherwise.
What can be done?
Surely our native oaks have been through droughts before. So the oak trees, other than the very small or very old trees, should be okay. Nonetheless, given the very low rainfall this year it may be prudent to give a valued tree in the urban landscape a “deep watering”.
A deep watering followed by soil drying for a month or two should not harm the tree. In fact, a deep watering may be the best recommendation for invigorating your thirsty oak tree, thus providing some insurance that the tree will survive this current drought.
I should mention that unless California receives normal or better rainfall the rest of the rainfall season, it is likely that early leaf drop will occur next summer. Remember, as suggested above, the early browning and fall of leaves does not mean that your tree will die. This is simply the tree's way of adapting to conserve water when soil moisture is low. Unless the tree is severely weakened by some other cause, it will leaf out normally the following spring.
For more information: Tietje, W., W. Weitkamp, W. Jensen, and S. Garcia. 1993. Drought takes toll on Central Coast's native oaks. California Agriculture 47(6):4-6.