Posts Tagged: oak woodland
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.
Oak woodlands are "some of the most biodiverse ecosystems in the North West," said UC Cooperative Extension forest advisor Yana Valochovic. "They are preferentially used by a lot of different bird species."
In the past, fires would burn out conifers and underbrush on oak woodland annually, but aggressive fire suppression is enabling them to spread unchecked, crowding out oaks.
Yanachovic is finishing a three-year research project on conifer encroachment, and AB 1958, if passed, would put policies in place so people can get rid of the conifers without jumping through as many bureaucratic hoops as before, the article said.
“It clarifies that the cutting of younger conifers out of oak woodlands does not qualify as conversion of timberlands,” she said.
But UC Cooperative Extension advisor Greg Giusti has found a surprising level of interest from the public in his Northern California research project about turkey vultures' nesting preferences in oak woodland.
“Animals with cute fuzzy faces are far more attractive in our culture,” said Giusti, a wildland ecology expert. “Turkey vultures have been overlooked. Very little is known about their biology and environmental needs.”
In the study area, the researchers counted 417 trees in all; seven of them had suitable nesting elements for turkey vultures. They found that the vultures at the Hopland facility select large hollow trees – either dead or alive, either shaded or in the sun – to lay eggs and rear their young. The tree species in the study included blue oak, interior live oak, Oregon white oak and valley oak.
“This is very different from other large birds, like eagles and osprey, who build open cup nests high up in tall trees, which they may use for generations,” Giusti said.
After turkey vulture chicks hatch, the parents drop into the cavity five or six times a day to feed their young, Giusti said. How birds with a five-foot wingspan traverse a deep vertical tunnel is a mystery.
“They just shimmy up and down, I would imagine,” Giusti said. “We don't know how the young birds do it when they fledge. We've never witnessed the adult birds calling them out.”
Giusti said the scientists will continue to build on the turkey vulture nesting database they have started with results from this project. In the coming years, they hope to learn whether turkey vultures will re-use successful nesting sites and whether they may be found nesting in fallen logs or rock piles.
In the video clip below, a turkey vulture explores a possible nesting cavity at the UC Hopland REC.
An initiative to maintain and enhance sustainable natural ecosystems is part of the UC Division of Agriculture and Natural Resources Strategic Vision 2025.
In addition, several studies have found that open space and residential properties containing oak trees have higher property values than those areas without oak trees. Ecosystem services provided by oak forests and savannahs include recreational opportunities, shade and shelter, increased property values, aesthetic values, erosion control, air and water filtration, and food and fuel.
However, the threats to oaks are many:
- Construction removes entire trees or damages the root zone resulting in oak tree death
- Subdivision of property and fragmentation in land use reduces open space for oak savannah and forest, threatening seedling recruitment in some oak species
- Inappropriate landscaping practices, designed to support exotic landscape species, threaten oak health
To ease the impacts of these threats, UC Cooperative Extension Central Sierra will bring oak education to five counties in the Sierra Nevada foothills – Amador, Calaveras, El Dorado, Mariposa, and Tuolumne. Public meetings and multiple-session training seminars will help educate land owners, policy makers and Master Gardeners in ways to protect, enhance and regenerate natural oak woodlands. Training will also provide information that Master Gardeners can disseminate to their clientele to help home owners protect landscape oaks.
The program is funded with a grant from Renewable Resources Extension Act (RREA), a USDA-administered program that serves to sustain the nation's forest and rangeland resources for future generations. According to the USDA National Institute of Food and Agriculture website, “RREA serves a broad array of forest and rangeland stakeholders, including landowners and managers, natural resource professionals, forest products industry, range-based cattle industry, and non-consumptive.” Recognizing that, as the website notes, “the sustainability of the nation's forest and rangeland resources is largely dependent on the actions of millions of private forest owners, farmers, ranchers, and land managers,” this series of educational workshops will focus on providing information to a broad audience.
In Tuolumne County on May 13, the Biological Resources Review Guide Ad Hoc Committee of the Board of Supervisors will meet to discuss various county policy options regarding oak mitigation. Richard Standiford, UCCE specialist in the Department of Environmental Science, Policy and Management at UC Berkeley, will address the committee, presenting his research related to oaks and property values. He will also provide information regarding mitigation policies.
On May 9, the Calaveras County Master Gardeners will receive the first session of an oak ecology, identification and landscaping practices workshop. They will identify oaks in the field, inspect trees damaged by construction and look for evidence of insect and other wildlife interactions. This will be followed by an interactive discussion exercise about how (or why not) to landscape around oaks. Standiford will visit the foothills at a later date to present oak ecology information to Master Gardeners.
The beauty of rolling hills studded with majestic oaks, other trees and shrubbery isn't the only reason to regenerate vegetation. The trees and shrubs create a much more hospitable habitat for a wide assortment of wildlife. Oak woodland vegetation also protects the quality of California water. The majority of the state's water flows through oak woodlands in streams and rivers that support fisheries, farms and cities. Plants and trees anchor the soil, preventing erosion and stream sedimentation.
One of the difficulties ranchers face in regenerating trees is supplying water for seedling establishment. Ranches often stretch for thousands of acres. Hauling water to remote sites or installing irrigation can be prohibitively expensive.
Third-generation San Miguel rancher George Work heard about a new tree establishment invention from Holland – a Groasis Waterboxx. Over the years, Work has collaborated with UC Cooperative Extension on oak planting projects and consulted with UCCE experts about squirrel diseases, ranch animal vaccinations and pasture management. He turned to UCCE natural resources advisor Royce Larsen for his thoughts on the Waterboxx.
“Because of Royce here, our Cooperative Extension agent, he provided a little added incentive when I wanted to try this thing,” Work said. “Royce said, ‘I'll help you.' Well, that was enough to get the job done.”
Work, Larsen and UC Cooperative Extension natural resources specialist Bill Tietje installed 10 Waterboxxes, which cost about $30 each, in a remote area of the 12,000-acre Work Ranch in southern Monterey County. Other plant regeneration methods – including traditional drip irrigation and tree teepees – were also installed for comparison.
The Waterboxx is a round plastic hat box-shaped reservoir that fits around the seedling trunk. When the seedling is planted, the reservoir is filled with about four gallons of water. A rope on the bottom continuously wicks moisture to the plant roots.
The box is covered with an inward-slanting corrugated top that cools during the night and channels condensed dew and fog into the reservoir, keeping it full of water. The Waterboxx provides a protective barrier around the trunk and shades and cools the soil beneath. At the Work Ranch, the plants are also enclosed in bale-wire fence to keep out wildlife poking around for water or hungry for tender green growth.
“The trees are doing surprisingly well," Larsen said. "In just three months, the seedlings have grown more than two feet."
Larsen said he will continue monitoring the project to see if the self-watering system can establish trees. If successful, UC scientists may study the Waterboxx more thoroughly in a replicated research design in Monterey County, San Luis Obispo County and other parts of the state.
See the components of a Waterboxx in the video clip below.