Posts Tagged: oaks
Native oaks stressed by drought may recover
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?
The situation
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 can be accomplished by moving a hose around under the tree's canopy during the day for a day or two at a low flow or a trickle stream, such that the water percolates into the soil, not simply run down the hill. Water a few feet away from the base of the tree to avoid inviting damage from crown rot caused by the fungi Phytophthora cinnamomi. Water-saturated soil increases the chances of infection of the tree trunk.
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.
UC researchers discuss oak health in LA
The goldspotted oak borer continues to threaten oak trees, Tom Scott, area natural resource specialist located at UC Riverside, told participants at conference on sustaining native oak woodlands in Los Angeles, the Monrovia Patch reported.
Scott said there is still a quarantine on moving firewood out of San Diego County to prevent the spread of the damaging insect.
Reporter Sandy Gillis wrote that Larry Costello, UC Cooperative Extension environmental horticulture advisor emeritus, described the power of oaks to access water deep in the soil.
UC adds 4,584 acres of forest to its research lands
The Los Angeles Times and San Francisco Chronicle reported on UC's acquisition of 4,584 acres of Northern California mixed-conifer forest as part of a PG&E bankruptcy settlement.
Debra Levi Holtz, who wrote the article for the Chronicle, quoted Keith Gilless, dean of the UC Berkeley College of Natural Resources, which houses the UC Center for Forestry, as saying, "For us, this is a dream come true to have a network of research sites on a north-south transection through the Sierra Nevada and Cascade ranges that will dramatically improve our capacity to do work on forest ecosystems that is responsive to the questions we all have about the impacts of climate change on those regions."
San Luis Obispo County ranch featured in newspaper story
The cover story in the Feb. 4 edition of the color magazine New Times is a well-written 2,300-word history of Avenales Ranch, east of San Luis Obispo, which has been the site of UC collaborative research for decades.
The story centered on 92-year-old family patriarch Jim Sinton, who inherited the 12,000-acre ranch from his grandfather. The owner of a local general store, Sinton's grandfather provided goods on credit to homesteaders who held the property in the late 1800s. As they went broke, he acquired the land and assembled the vast acreage where today cattle run, majestic oaks dot the landscape and a hunting club helps generate income.
Sinton, a UC Berkeley agricultural economics alum, helped design and execute an experiment in the early ’60s to test the validity of ranchers’ then-accepted belief that acorns were harmful for cattle to eat. According to the story, he concluded that the presence of oak trees on a grazing range is beneficial.
Writer Kathy Johnston spoke to San Luis Obispo County-based UC Cooperative Extension natural resouces specialist Bill Tietje, who said the ranch is “one of the hotspots in the county” for mountain lions and bears. He told the reporter that 100 species of birds, a dozen types of small mammals, plus bobcats, gray foxes, and a variety of reptiles and amphibians can be found on the ranch. The mix of wooded areas, chaparral and grassland the Sintons have maintained supports the wildlife, he said.
The article mentioned that the Sinton family occasionally opens the Avenales Ranch to the public by hosting UC Cooperative Extension workshops on oak regeneration.
Plants are feeling the 2008 drought
The first indicator cited in a San Jose Mercury-News story about the 2008 drought is the number of phone calls coming into the local UC Cooperative Extension office.
The second paragraph of the article says the "unusual number of calls" are from people asking why their camphor trees and liquid ambars are wilting.
"This year we've had so little rain that for trees that are not adapted — and even those that are — there is simply no moisture in the ground except for (what) we are applying," the Mercury-News quoted Bethallyn Black, UCCE urban horticulture advisor in Contra Costa County.
She said some areas have even less water in the ground because the water table has fallen below the reach of trees whose roots have not adapted to a Mediterranean climate, according to the article.
The Mercury-News article, written by Rowena Coetsee, runs parallel to a press release distributed by the UCCE News and Information Outreach office last week that noted native blue oak trees in foothill areas are losing their leaves and turning color way before normal.
According to UCCE oak specialist Douglas McCreary, the ability to shed foliage early is a survival mechanism of the native trees. When faced with low soil moisture, the trees can either keep their foliage and continue losing water through leaf pores, or drop their leaves and conserve moisture. In the long term, shedding leaves keeps the trees from drying out completely and dying.
Native blue oak trees.
UCCE advisor's media relations may save lives
UC Berkeley Cooperative Extension natural resources specialist Doug McCreary knew it was a matter of life or death . . . . This spring, landowners were wondering whether they should yank out oak trees that were uncharacteristically brown or bare.
McCreary took quick action to save trees' lives. He gathered information for a news release assuring people the die-back was probably not a sign of Sudden Oak Death and urging them to wait at least a year before pulling out trees. The story was picked up by the Associated Press and run in several Northern California newspapers, including the San Francisco Chronicle and San Jose Mercury News.
The AP article included McCreary's points that many oaks in the Sierra foothills and along the North Coast have been left leafless this spring because of a cold snap, not disease. Most trees should recover.
Meg McConahey of the Santa Rosa Press Democrat called McCreary to localize the story. Her article said landowners and forest stewards on the North Coast are particularly sensitive to oak health because of the devastating spread of SOD. "Sonoma is by far the hardest hit of 14 counties now under state quarantine in California," the article said.
Oak tree damaged by spring frost.