- Author: Jeannette Warnert
Reposted from the UCANR News
California oak woodlands are highly prized ecoregions where stately trees, many of them hundreds of years old, are cornerstones of a habitat for wildlife and native plants. Sadly, some of these ecosystems are seriously threatened by exotic pests and diseases, encroachment by less desirable vegetation, and wildfire.
Each year, UC Cooperative Extension hosts workshops to share scientific developments aimed at conserving these important habitats – and the economic value of ranching – on oak woodlands, which are found on the lower elevation slopes of the Sierra Nevada, the Coast Range and other foothill areas of California.
Typically, the workshops are held in person and draw moderate-sized audiences for presentations, questions and answers, and field trips. Because of the COVID-19 pandemic, this year's workshop was offered online in April with pre-recorded presentations available for viewing at the participants' convenience and a live question-and-answer session on Zoom.
The retooled event garnered 500 registrants, over 300 views of the YouTube videos and 140 participants in the live Q&A session. The presentations and Q&A session are still available online for future viewing as well at http://cemendocino.ucanr.edu/Forestry/Workshops/California_Oak_Health.
“People from all walks of life participated, including those with professional and personal interest in oak woodlands,” said Yana Valachovic, UCCE forest advisor in Humboldt and Del Norte counties and a conference organizer.
Presentations at the 2020 conference included the following topics:
Encroachment by Douglas-fir
In Northern California, the biodiversity of oak woodlands is being threatened by Douglas-fir encroachment. The oaks' shade helps the young conifers get established with protection from harsh sun. In time, the fast-growing Douglas-fir trees pierce the oak canopies and begin to crowd out the areas' native understories, which are important for the diversity of birds, mammals and reptiles attracted to oaks.
As the Douglas-fir continue to grow and multiply, they threaten the very lives of the oak trees and the unique ecosystem they dominate.
To better understand the Douglas-fir encroachment, Valachovic established 10 research sites in Humboldt and Mendocino counties to gather information about the fate and the age of oaks. She and her research partners determined the ages of the oaks and firs, and counted the seedlings, saplings, snags and understory vegetation.
“With this research, we were able to demonstrate that even though the oak trees can be smaller in diameter, they are much older than the Douglas-fir trees,” Valachovic said. “The encroachment process is happening quickly, and the oaks are falling out of the system.”
The shift appears to have been initiated in the mid-19th and early-20th centuries, coinciding with the Gold Rush and wildfire suppression.
With the data confirming Douglas-fir encroachment, Valachovic turned her attention to oak woodland restoration. At 14 sites in Humboldt and Trinity counties, her team studied the effects of Douglas-fir removal.
“Grasses and forbs under the oaks reestablished. Diameter growth on the oaks increased,” she said.
These research findings contributed directly to changes in policy that had previously limited landowners' ability to remove and sell conifers encroaching on oak woodland. The research also helped create new funding opportunities to support oak woodland restoration and conservation in Northern California.
Case study of oak woodland wildfire recovery
In July 2018, about two-thirds of the 5,289-acre UC Hopland Research and Extension Center was burned by the River Fire.
The transformation of the land, which had likely been without a large wildland fire for at least 100 years, was intense and stressful, said UC Cooperative Extension forest advisor Michael Jones. However, it also provided a unique opportunity for researchers to compare the impact of wildfire on the resiliency of vegetation on grazed and ungrazed oak woodland.
Jones established 35 one-fifth acre research plots at the research center and collected data two months following the fire and one year later. The research will continue in the future to better understand long-term impacts, but Jones was able to share revealing early results at the workshop.
Right after the fire, in severely burned areas areas, the future of the oaks looked ominous. Jones predicted 40% tree mortality.
“The oaks were exposed to persistent, intense heat. They were cooked,” he said. “But two months after the fire, we were already seeing basal sprouts. This was an amazing response by the trees. Oaks are pretty damn tough.”
A year after the fire, surveys showed that tree mortality in the burned areas was 25%, much less than Jones' early predictions. While some management for specific situations in severely burned areas may be necessary – such as removal of hazard trees, reducing fuels in defensible spaces or removal to control invasive species – the results of this work show the trees recover naturally.
“Esthetically, I know these systems aren't as pleasing as they were before, but ecologically, they are healthy and recovering,” he said. “In 100 years, it will look just as good as before the fire.”
Fire impacts in woodland areas previously grazed and not grazed
The fire on the research station also permitted Jones to compare the fire's differing impact on non-grazed and grazed oak woodland. At first, the grazed areas looked almost unscathed with minimal flame scorching on the bark, while an area where the pasture hadn't been grazed for 25 years had evidence of much higher severity fire.
“Grazing is a phenomenal way to help manage fuels,” Jones said. However, the grazed areas displayed ecological shortcomings a year later.
“In grazed pastures, the large mature trees were still alive, but there was no oak regeneration (basal sprouting or seedlings),” Jones said. “In the ungrazed area, a lot of biomass had been killed, but there's nearly 100% resprout of oak trees and we have an impressive amount of oak seedling recruitment.”
Jones said he isn't discouraging grazing.
“But it is important to protect sites from grazing, and especially wildlife browse, when a landowner or land managers' objectives are to regenerate or conserve oak woodlands,” Jones said.
New ambrosia beetle another threat to California oaks
Akif Eskalen, UC Cooperative Extension specialist in the Department of Plant Pathology at UC Davis, has identified a new insect-fungus team that causes oak borer wilt in Northern California Valley and Blue Oaks. It is an ambrosia beetle, commonly known as Mediterranean Oak Borer, which carries several fungi in its mouth. The beetle bores into the tree and introduces fungi to grow for food. The fungi spreads and disturbs the transportation of water and nutrients, causing wilt in the tree.
The oozing and staining lesions on the bark are similar to other oak fungal diseases, such as sudden oak death. The beetle – native of Mediterranean basin countries in Africa, Asia and Europe – cannot fly far, so most likely is transported for long distances on infested firewood.
During the workshop, Eskalen suggested not moving firewood, removing heavily infested trees and chipping infested wood into 1-inch particles to reduce the spread of the ambrosia beetle and its fungal partner. He asked viewers to report any suspected oak tree infestations to the local agricultural commissioner, CDFA Diagnostic Laboratories, UC Cooperative Extension advisors or CALFIRE. Chemical options for sparing oaks from the ambrosia beetles' devastation are under investigation.
Threats to oaks and other native plants from root rotting Phytophthora
Restoration plantings have inadvertently introduced plant pathogens to native oak woodland ecosystems in California, said Ted Swiecki of Phytosphere Research, an organization that provides consulting services related to natural resource management, horticulture, urban forestry and agriculture. The group of pathogens causing the damage are largely from the Phytophthora genus, first described in the 1860s. The name translates from Greek to “plant destroyer.”
Swiecki has observed when Phytophthora infested plants and soils are introduced to native habitats, the pathogens can attack various native plants, including toyon, madrone, manzanita and full-grown oaks. Once established, the pathogen can spread along drainages, by moving soil from one area to another and by hitchhiking on equipment, tires and hiking boots.
The pathogen can easily be overlooked at nurseries, which, by their nature, have conditions that favor Phytophthora development. Plants at nurseries are well watered, have high root density and are often placed on the ground where they can pick up pathogens.
He said the best approach to tackling Phytophthora is not using nursery stock for restoration or beautification of natural oak woodland. Direct seeding, using natural regeneration, or onsite propagation are safer ways to enhance vegetation in oak woodland.
“It's easier to prevent Phytophthora from being introduced in the first place and much cheaper and more effective than trying to eradicate it later,” Siewcki said.
Finding an Ecological Niche: Selected Foothill Woodland and Chaparral Species, Part 1 of 3: The Blue Oak
By Laura Lukes, UC Master Gardener of Butte County, February 22, 2019
[Note: Blue oak (Quercus douglasii), gray pine (Pinus sabiniana), and buckeye (Aesculus californica) are three species that thrive in rugged local foothill woodland and chaparral habitat. Today and in the following weeks, this series will look at these species and the adaptive strategies they have evolved over time to thrive in their challenging environment.]
What drives the evolutionary journey of the flora and fauna that populate our globe?
Some species cooperate by sharing resources. For example, in Tortuguero, a tiny strip of beach along the northeastern shoulder of Costa Rica, four separate species of sea turtle lay their eggs each year. They migrate to the beach at different times, ranging from early March to October, and feed on different resources. Millions of turtles, and untold numbers of their babies, have shared the same tiny piece of real estate for eons.
Here in our own backyard, there are species that have evolved to exploit ecological niches that very few others claim. These are the various oaks, conifers, and woody shrubs that populate the foothill woodland and chaparral zone of the Western Sierra Nevada and Coast Range mountains. A dominant species in this environmental nook is the blue oak (Quercus douglasii). According to Andrew Conlin, Soil Scientist with the Natural Resources Conservation Service (NRCS), “the presence of blue oak woodlands indicates really rough growing conditions: shallow, tough soils” as opposed to the rich loamy soils of the valley, which are preferred by valley oaks.
Quercus douglasii also goes by a number of other common names, including white oak, mountain oak, mountain white oak, and iron oak. But it acquired its most familiar and descriptive common name from the same person from whom its Latin binomial (scientific name) is derived. In 1831 David Douglas, a Scottish botanist, christened it the blue oak for the bluish cast of its deeply lobed leaves. (A digression: Douglas, for whom the Douglas-fir and hundreds of other western plants are named, lived from 1799 to 1834. He made three trips to the American Northwest between 1823 and 1831, encountering the blue oak on his last trip while traveling from the Columbia River in Oregon to San Francisco. He died under curious circumstances, apparently after falling into a bull trap while climbing Mauna Kea in Hawai'i.)
Blue oaks are native to California's foothills, South Coast Range, North Coast Range and San Francisco Bay Area, forming a botanical loop around the Central Valley. Depending on the source consulted, these trees average between 30 and 80 feet tall. But all sources agree that the blue oak is the most drought tolerant of all the deciduous oaks in the state.
Surviving Drought and Fire:
Adaptations to survive the long, hot, dry summers and sparse winter rains of our Mediterranean climate include thick leaves with a bluish-green color. According to the US Department of Agriculture (USDA), blue-gray-green leaf color reduces heat absorption. During severely hot and dry years, blue oaks will sometimes shed their leaves and go dormant to conserve energy, allowing these tough little oaks to survive temperatures above 100° F for several weeks at a time. Like many plants growing in marginal soils, blue oaks are slow growers, usually increasing only a few inches each year.
Although blue oaks can tolerate fast-burning grass fires, they have less success in surviving hotter brush fires, according to University of California Department of Agriculture and Natural Resources (UCANR). If a tree does survive a fire event, it can reproduce both through seeds and by sprouting from burnt stumps. Blue oaks can produce sprouts after a low- to moderate-severity surface fire, and younger trees have the edge on older trees for fire survival odds. On younger trees, the light-colored bark (hence “white oak”) is thick and helps reduce fire damage, the USDA notes, whereas the bark of mature blue oaks is thin and will flake off as the trees age, making older blue oaks less insulated against fire. After a fire, blue oaks can also re-establish from acorns that have dropped from surviving parent trees and/or been dispersed by animals, among other possibilities.
USDA research also reveals that the blue oak's post-fire recovery is likely aided by the fact that it withstands extreme drought by dropping leaves under water stress and producing a flush of new leaves when wet weather returns. In fact, in wet years, crown-scorched blue oaks may produce a flush of new leaves soon after fire.
Native American Uses:
All parts of the blue oak were woven deeply into the culture and survival of California's native peoples. It was one of more than a dozen oak species whose acorns contributed a major source of dietary nutrients and calories. Because of their superior flavor, blue oak acorns were among the most commonly gathered.
A Plant Guide published by the Natural Resources Conservation Service (NRCS) provides an exhaustive list of the ways California Native Americans used blue oak wood, bark, and acorns, including as “medicine, dyes, utensils, games, toys, and construction materials.” Locally, the Maidu used oak shoots to frame cradleboards and oak posts to construct shelter, and the Yana used an oak paddle in cooking. Traps for birds were baited with acorns, and split acorns became dice for gambling.
Besides providing physical sustenance to native peoples, I imagine that the peaceful beauty of blue oak woodlands fed their souls. Twisted, dwarfed blue oak silhouettes are a classic component of the California landscape. These trees are prime examples of successful adaptation to truly demanding habitat and climate conditions.
Sources and further information:
UCANR: Oak Woodland Management: Blue Oak
NRCS:BLUE OAK: Quercus douglasii Hook. & Arn.
Rising From the Ashes
Master Gardeners are taking note of the vegetation emerging on property destroyed by the Camp Fire. On Fay Crociani's Upper Paradise lot, native salvia reappeared in early January, sprouting from roots of plants that had burned to the ground. A potted erodium (Alpine geranium) also showed leaves in January, followed in February by green leaves emerging from desiccated black iris rhizomes. More irises, planted in plastic pots, survived the fire even though the plastic melted around them, and other plants and leaves continue to rise from the scorched ground. Fay encourages folks to watch and see what comes up before totally digging up an area. She says “there is real magic and joy in my heart when I spot new growth. I know hundreds of plants will never come back, but many, many will if we have the patience to wait.”
/h2>- Author: Jeannette E. Warnert
Researchers with UC Agriculture and Natural Resources (UC ANR) have worked with landowners for decades to help them manage these oak woodlands in ways that balance the ranchers' economic needs with ecological considerations.
In the late 1990s, Tulare County ranchers Jim and Gay Versteeg were interested in thinning their blue oak stands in order to improve biodiversity of the forage growing on the land. The family offered UC ANR researchers three acres to study blue oak tree management practices to better understand the impacts of various thinning practices.
For thousands of years, fire was an important part of California's oak woodlands. Native Americans and, more recently, ranchers set fires to improve habitat and enhance desirable vegetation. However, aggressive fire exclusion during the last 30 years has led to significantly denser stands of blue oak trees.
“We looked into the fire history on the Versteeg ranch,” said Richard Standiford, UC ANR Cooperative Extension specialist based at UC Berkeley. “It burned about every 13 years prior to 1965, but since then, there have been no fires at all.”
Standiford conducted the study with two San Joaquin Valley-based Cooperative Extension natural resources advisors, Neil McDougald of Fresno and Madera counties and Ralph Phillips of Kern County. One-third of the study area was moderately thinned, and one-third was heavily thinned. For comparison purposes, the researchers left one-third of the study area untouched. The study area excluded livestock, but it was accessible to deer and rodents.
“The Versteegs thought that, with more sunlight, the amount of native grasses would increase, but that wasn't the case,” Standiford said. “The vegetation in all the plots was mostly grasses and forbs that were introduced after Europeans began settling California, as it is in most oak woodland around the state.”
Thinning did result in the growth of younger trees from stump sprouting.
“We want the sprouts to come back to provide the next generation of trees so when the big ones die or blow over, there are young trees to take their places,” Standiford said. “The main way in which blue oaks regenerate is sprouting from stumps.”
Acorn production on a landscape scale was not impacted by thinning. Trees in the thinned plots produced more acorns per tree, however, because there were fewer trees, the same amount of acorns per acre was produced.
Standiford shared the results of the study with ranchers, land managers and researchers at the 7th California Oak Symposium in 2014; the research will be published in the symposium proceedings later this spring. He said the study results validate for landowners that thinning is an appropriate management practice on blue oak rangeland. Forage increases, the trees survive and grow back.
“If ranchers intend to thin every 15 years or so, moderate thinning is acceptable,” Standiford said. “If this is something they would do every 30 years, they could thin heavily.”
An initiative to maintain and enhance sustainable natural ecosystems is part of UC Agriculture and Natural Resources Strategic Vision 2025.
- Author: Douglas McCreary
- Editor: Sophie Kolding
Towards the end of January, an unusual phenomenon occurred in the Sierra foothills - some of the blue oaks began leafing out. While the vast majority of trees remained leafless, one could see occasional light-green canopies interspersed with their bare neighbors. This is unusual in that the earliest leaf-out most people recall observing doesn’t start until late February or early March.
So what is causing this? Clearly the weather pattern this past winter has been very unusual in terms of precipitation. There was abundant early rainfall in October and November, followed by a December and January that were some of the driest on record. However, dormancy and its subsequent breaking are much more controlled by temperature than by rainfall. That is, a significant period of cold is necessary before most temperate plants resume growth in the spring. Photoperiod – or the relative daily lengths of light and darkness - also often plays an important role but this obviously doesn’t vary from year to year.
Has the temperature pattern been abnormal? The CIMIS (California Irrigation Management Information System) long-term data was compared with this past winter’s averages and nothing stood out as particularly different, although there is apparent, large variability from year to year. There was a day or two of somewhat colder-than-average temperatures in mid-January, but below-freezing temperatures in the foothills occur almost every year. Therefore, at this point, the cause of early leaf-out remains a mystery.
![Doug leafing out II Doug leafing out II](http://ucanr.org/blogs/OakCon/blogfiles/10351.jpg)
What about the impacts? It is likely that some of these “early leafers” will suffer frost damage. This occurred several years ago in mid-spring when there was an unusually late freeze and many blue oaks had their foliage killed back. Most of this occurred at mid-elevations, presumably because trees at higher elevations hadn’t leafed out yet, and those at lower elevations were so far advanced that their foliage was hardier. While this certainly wasn’t good for the trees, they were able to recover and produce a new crop of leaves within a month or 6 weeks and no increase in mortality was noted. It seems likely that, as a species, blue oaks have evolved individuals that leaf out at different times of the year so that at least a portion of their population can take advantage of different weather conditions. The “risk takers” might get hammered now and then, but under the right conditions, they can take better advantage of unusual weather patterns than their more conservative colleagues. In the event of significant warming in California as a result of climate change, these may even be better adapted to survive and prosper in a changing environment.
- Posted By: Sophie Kolding
- Written by: Jim Sullins and John Maas
Four head mature cows have been reported dead in Tulare County foothills from 2500 feet to 1000 foot elevations. All were in the vicinity of Blue Oaks with heavy crop of acorns.
Neil McDougald, Livestock Range Advisor of Madera County indicated that this year is similar to other years he has seen where there have been incidents of acorn toxicity. There is a very large acorn crop, and recent rains has led to some early green-up under Oak Trees which can result in some cows camping and eating an overload of acorns resulting in acorn poisoning.
Most cattle in California spend at least part of the year in areas where oak trees abound. Health problems due to ingestion of oak leaves or acorns are certainly not an everyday problem; however, when problems do occur they can be catastrophic. Several years ago, in a few northern California counties, about 2,700 cattle died due to oak toxicity1.
Some years have much higher production of oak acorns than others and this year, 2011 in the Foothill Ranges of the Southern Sierras, has been reported as one of the highest production years observed. In addition early rains may increase the risk of acorns by reducing the nutrient value of last year’s forage, as well as causing an early greening of grass under the oaks where acorns are accumulating.
During the week of October 10, 2011 four head mature cows were reported to be found dead in Tulare County foothills from 2500 feet to 1000 foot elevations. All were in the immediate vicinity of Blue Oaks with heavy crop of acorns. These cattle were not available for necropsy and cause of death was not confirmed, however oak acorn toxicity is suspected.
Oak toxicity symptoms usually appear when cattle eat 50% or more of their diet as oak (acorns, leaves, buds). Toxicity can be prevented by supplementing cattle with hay or other supplements when forage conditions are poor and acorns are abundant. A higher risk may occur if early or late snowstorms covers available forage and knocks down oak limbs with large amounts of buds and young leaves or acorns, be sure to start hay supplementation immediately. A delay of only a day or two could result in many deaths.
There are two recommendations to avoid cattle loss due to acorn toxicity. One is to provide supplement to draw cattle away from the acorns, so that their exposure decreases. The other is to remove cattle observed eating acorns from fields with high levels of acorns.
It is recommended that producers work with their local veterinarian and/or diagnostic laboratory, to be certain of the actual cause of death in all livestock losses. There are many other factors that can cause sudden death and although oak toxicity may be likely and immediate actions should be taken to prevent further deaths, a follow up with a veterinarian is often the best course of action to prevent further losses. For a more comprehensive discussion on identification and recommended actions for Oak Toxicity and Acorn Calf syndrome in cattle please refer to the link below.
Dr. John Maas, UC Davis Extension Veterinarian, informative article on oak toxicity (OAK TOXICITY UCD Vet Views California Cattleman, Jan 2001):
http://www.vetmed.ucdavis.edu/vetext/INF-BE_cca/INF-BE_cca01/INF-BE_cca0101.html.Blue Oak Acorn
Cattle Pasture amongst Blue Oaks