Forest Research and Outreach Blog
Genetic detective work by an international group of researchers may have solved a decades-long mystery of the source of a devastating tree-killing fungus that has hit six of the world's seven continents.
In a study published September 1, in the peer-reviewed journal Phytopathology, California emerged as the top suspect for the pathogen, Seiridium cardinale, that is the cause of cypress canker disease.
It was in California’s San Joaquin Valley in 1928 that S. cardinale was first identified as the culprit causing the disease. The fungus has made its way since to Europe, Asia, New Zealand, Australia, South America and Africa. In many regions, the pathogen has infected and killed up to 95 percent of native trees in the cypress family, including junipers and some cedars.
"The fungus was likely introduced from California either in the South of France or in Central Italy 60 to 80 years ago, and that introduction resulted in a global pandemic that has devastated the region's iconic Italian cypress trees," said Matteo Garbelotto, adjunct associate professor and Cooperative Extension specialist in ecosystem sciences at UC Berkeley.
The fungus kills a tree by entering through cracks in its bark, producing toxins that wreak havoc with its flow of sap and choke off its supply of water and nutrients. The disease has left an indelible mark throughout Southern Europe.
Infected Monterey cypress trees in California's Central Valley. (Photo by Gianni Della Rocca)
"Italian cypress trees are important to the ecosystem, but they are also considered the quintessential trees of the Mediterranean, the ones that dot the Tuscan countryside and that form the landscape of much of Greece, the South of France and Spain," said study lead author Gianni Della Rocca, researcher at the National Research Council in Florence, Italy. "It is difficult to put a price tag on the impact this pathogen has had. It's hard to imagine the Tuscan or Provence landscape without cypresses."
The relatively sudden appearance and destructiveness of the disease in Europe pointed to an exotic pathogen, but scientists didn't know where it came from. Tracing the origins of the pathogen back to California took some genetic sleuthing by Garbelotto, Della Rocca and their colleagues Catherine Eyre, a UC Berkeley post-doctoral researcher in ecosystem sciences, and Roberto Danti, a researcher at the Italian National Research Council.
The researchers used modern DNA fingerprinting techniques to analyze 96 S. cardinale isolates of diseased tree samples from seven Mediterranean countries, eight California counties, Chile and New Zealand.
S. cardinale is capable of reproducing asexually by creating genetically identical clones of itself, or sexually when a different variant is available for mating.
California emerged as a likely culprit because it hosts populations of the pathogen that are genetically diverse, a strong sign that the pathogen is endemic to the region, the researchers said. The study authors attribute the diversity to the likely sexual reproduction of two genetic variants of the pathogen found in California.
In contrast, the researchers found that one of the two variants of S. cardinale endemic to California is responsible for the epidemic of cypress canker in the Mediterranean, an indication that the fungi there all descended from a "founder" genotype that made its way to Europe.
The second variant found in California, incidentally, has been linked to the epidemic in countries in the Southern Hemisphere such as New Zealand and Chile.
Just how the pathogen moved from California outward is not yet clear, the researchers said. What they can say with certainty is that humans helped the pathogen along in its journey, since air and sea currents alone could not account for the discovery of identical genotypes thousands of miles apart. The paper reports that strains of the pathogen with identical DNA profiles were found hundreds to thousands of miles apart, an indication that humans are actually moving the pathogen, most likely thorough the trade of infected plants.
Following completion of the study, the researchers looked through historical catalogues of large commercial nurseries in Italy and France and found records of mature Monterey cypress trees for sale during the late 1920s and 1930s, indicating significant imports of the California trees and their seeds at that time.
"It is very likely that the pathogen was introduced during that period," said Danti, who added that interviews the research team conducted with people who worked in the nurseries then suggested that cypress canker disease was becoming a problem by the late 1930s.
The researchers found three progenitor strains of the pathogen only in Tuscany, indicating that the disease was brewing there for several generations before exploding beyond the region's borders.
"It could have easily taken 10 to 20 years from the time of introduction for the first major outbreak to occur," said Garbelotto. "In Italy, the pathogen was first identified in 1951, so it could have arrived decades earlier."
The study authors advocate the genetic screening of plants to stem the spread of the disease, just as plant shipments in and out of California are now tested for the Sudden Oak Death pathogen.
"We can develop tests to screen for the presence of S. cardinale on plants that are traded, and even to test for the presence of strains that are currently not present in Europe or in the Southern Hemisphere," said Garbelotto. "Technological advancements of the last few years allow for the easy development of such tests, but it was essential to figure out the source of the pathogen in order to know what to look for."
Garbelotto said that researchers in Europe have spent the past three decades developing cypress trees that are resistant to the current variant of S. cardinale in the region.
"There is no assurance those resistant trees will be resistant to other strains from California, if they are introduced," said Garbelotto. "If another strain were to be introduced into the Mediterranean or in the Southern Hemisphere, this could accelerate and worsen the epidemic in those regions. It could nullify a 30-year long effort to develop trees that are resistant to the pathogen.
“It is imperative to stop the movement of infected plants in order to avoid further introductions that could completely overcome those lines of resistant trees."
Be careful what you plant
The new study spotlights the hazards of planting trees and other vegetation in regions where they are not native. Garbelotto said consumers should be careful about what they choose to plant in their backyards.
"Gardeners tend to pick the easiest plant to grow," said Garbelotto. "Monterey cypress became very popular in Europe because they grow faster, and they grow really well along the shore, while the Italian cypress is better suited for inland regions. The popularity of the Monterey cypress may have inadvertently led to the devastating spread of a deadly fungus throughout the world."
Garbelotto added that the cypress canker pathogen is so aggressive that, even in California, it can kill trees that are planted outside of their natural range.
"When Monterey cypress trees are planted in Monterey or along the coast, they are resistant to the disease," said Garbelotto. "That suggests that in coastal areas, the environment is unfavorable for development of infections, despite the pathogen having been in California for a long time. The pathogen emerges when we place the tree in a foreign environment."
Garbelotto said that chemical treatments for cypress canker disease may become available in the near future, but they are costly, and their effects on the environment are not clear, so prevention is preferable.
To confirm the connection between California and Mediterranean populations of the pathogen, the researchers have conducted a follow-up study using more than 200 genetic markers of S. cardinale isolates. Results of the study should be available within the next year.
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Re-posted from UC Berkeley Department of Environmental Science, Policy, and Management.
This image from a Nelder Plot at Blodgett Forest Research Station in the Sierra Nevada mountains is part of a study designed to find out how trees respond to different levels of competition for resources (light, water, and nutrients). The wagon-wheel pattern provides a space-efficient way to experimentally increase tree density as one gets closer to the center of the “spokes.”
The trees in the image are giant sequoia, a species that is particularly sensitive to competition. After only a few years, one can see from the image that trees near the center of the spokes are smaller than trees near the edges where tree density is low.
The study has implications for how foresters manage tree density, depending on various objectives such as wildlife habitat, timber, or carbon sequestration.
Last week I visited Trinity River Lumber (TRL), a sawmill, in Weaverville, California. The sawmill was almost totally destroyed by a fire in September 2009 and completed rebuilding in January this year. The mill is the largest private employer in Trinity County with approximately 115 full time jobs. The community was relieved that TRL’s owner chose to rebuild the mill after the fire. The new mill is impressive in its versatility to saw a range of products and in its use of technology to maximize production. Both the pony (small log) and main headrig saws make use of 3D scanners to optimize lumber yield from each log. They are currently increasing production to approximately 120,000,000 board feet of lumber per year. The main products are green (undried) douglas fir and white fir dimension lumber.
TRL is classed as a SBA (Small Business Administration) sawmill by the Forest Service. This means that they are eligible to bid on Forest Service SBA set-aside sales (http://www.sba.gov/content/natural-resources-assistance-program). There are only four SBA sawmills left in California: TRL, Shasta Green, Sierra Forest Products and Sound Stud (currently curtailed). TRL do not own timberland and source logs, from public and private lands, within a 200 mile radius. Some logs sourced from the Sierra Nevada are delivered on flat bed trucks with log stakes so that the same truck can then take finished lumber to market.
As part of the UC Woody Biomass Utilization program (http://ucanr.org/sites/WoodyBiomass) I have worked with TRL on a number of projects including deploying new technology at the mill that increases the efficiency of sawing small logs. Most recently I worked with the mill to help them secure a 2011 Forest Service Woody Biomass Utilization (WBU) Grant. The grant of $250,000 was one of three awarded to California applicants (http://ucanr.org/blogs/blogcore/postdetail.cfm?postnum=5184) and will help pay towards the engineering required for a biomass fired boiler to run dry kilns with the potential to add electrical generation in the future. The project will allow TRL to produce kiln-dried lumber, increase the efficient use of sawmill residues and create a new market for woody biomass in the county.
Since 2008 the UC Woody Biomass Utilization program has helped capture almost $5m dollars for California businesses, non-profits and government though the WBU grant program. This represents a significant investment in helping the forest products industry in California retool for smaller logs and woody biomass from ecological restoration projects.
We have helped many businesses like TRL, non –profits and others with understanding technology, markets and sourcing grants – perhaps you could be next?
Woody Biomass Utilization Website (http://ucanr.org/WoodyBiomass)
Woody Biomass Utilization Blog (http://ucanr.org/blogs/WoodyBiomass/index.cfm)
Woody Biomass on Twitter (http://twitter.com/WoodyBiomass)
Wildfire Summit pulls together Tahoe basin residents and agencies on the fourth anniversary of the 2007 Angora fire to improve implementation of defensible space
The Lake Tahoe Wildfire Summit was held in Tahoe City on June 24th, 2011, four years after the Angora fire which started on June 24th, 2007 in South Lake Tahoe. The summit drew together over 100 basin residents, agency staff and policy makers to focus on ways to reduce wildfire risks to Tahoe homes and communities. Presentations centered on wildfire issues in the Tahoe Basin and how to reduce risk to homes and communities by creating defensible space, improving building materials and design, and implementing forest fuels reduction projects. Participants also went on field trips to the nearby Washoe fire, to a forest fuels reduction project implemented at Granlibakken resort (the hosting venue), and to a nearby neighborhood to examine the flammability of home construction.
After reaching a highpoint in 2007 due to the Angora fire, the level of concern about wildfire and motivation to do defensible space seems to be tapering off at the lake according to many fire agency staff. Participants cited residents’ and homeowners’ attitudes as the foremost barrier, saying that people don’t care about fire hazards, don’t think of natural vegetation as needing maintenance, or would rather recreate than do yard work. This attitude may be deeply ingrained at Lake Tahoe, a community where leisure and recreation in the “natural” outdoor environment is deeply valued.
Lack of understanding about the issue and denial that a wildfire could happen again were also cited with some reporting time they had been told by locals that Tahoe had an “asbestos” forest and wouldn’t burn. Other concerns are that vegetation removal for defensible space will look unsightly or reduce privacy. Also, there is a perception that defensible space actions are illegal or clash with water quality best management practice requirements required by local and regional government to preserve Lake Tahoe’s famed clarity.
Ownership patterns, including second home ownership and a high percentage of rental properties, reduce the opportunity and ability for some to complete defensible space. Costs are a factor for some residents, especially during the current recession (though there are currently rebate programs in place that can pay up to half of the cost of defensible space treatments). Disposing of materials can also be difficult.
Attendees at the Summit brainstormed and prioritized strategies to overcome these barriers to defensible space implementation. Education was cites as the major need to increase implementation. Education should focus on increasing awareness and understanding of the fire issue at Tahoe and highlighting the attractiveness of defensible landscapes. A major goal should be to develop a culture that doing defensible space is just a part of living at Lake Tahoe. Helping residents understand that defensible space is not only legal, it’s required and will eventually be enforced was also key. Following up with actual enforcement actions was identified as critical to this effort.
At the end of the day, all participants said the summit helped to clarify wildfire issues in the Tahoe Basin. 88% said it will help their communities work together to reduce wildfire risk and that they personally had a better idea of how to reduce wildfire hazards in their community.
Partner agencies included the seven local fire agencies in the basin, CalFire, the Nevada Division of Forestry (NDF), the Tahoe Regional Planning Agency (TRPA), the US Forest Service and both the University of California and University of Nevada Cooperative Extension. Funding for the event was provided by the NDF, TRPA, fire resistant construction material manufactures, and local defensible space contractors.
For a full account of the event, please download the Summit Report
For more information on how to implement defensible space at Lake Tahoe, go to: www.livingwithfire.info/tahoe
The Northern California Prescribed Fire Council provides continuing education opportunities for those using fire in forest management and conservation activities. Although prescribed fire councils are common in the U.S., this is the first such council in California. Council participants include public and private resource managers, researchers, firefighters, fire safe councils, tribes and regulatory agencies. The council hopes that by working together, this diverse group can increase individual members’ expertise in using fire for resource management and can improve fire-related education in the state. The council aims for a better public understanding of the value of prescribed burning in the state’s fire adapted landscapes, for increased safety in the use of prescribed fire, and for increased delivery of fire-related knowledge to land managers throughout the state.
Prescribed (Rx) fire is used in a variety of landscapes and contexts in northern California. The versatile nature of prescribed fire is evidenced by its diverse users, which include state and federal land management agencies, timber companies, tribes, non-governmental organizations (including fire safe councils), and private landowners, among others. Prescribed fire is complex in nature and successful implementation requires thorough planning. Major obstacles include:
- Narrow burn window (conditions, such as wind speed, relative humidity, and fuel moisture, do not fall within conditions outlined in the burn plan)
- Air quality regulations and environmental laws
- Lack of trained personnel
- Public opinion
- Lack of funding
- Liability/insurance limitations
The Northern California Prescribed Fire Council works collaboratively to improve techniques, increase training opportunities, and ameliorate permitting and other regulatory hurdles.
Join us at the fall meeting of the Northern California Prescribed Fire Council in November in Humboldt.