Forest Research and Outreach Blog
To see dwarf mistletoe seeds is to experience them. These are not typical seeds that gently drop from a mature plant. Rather, they are explosive — forcibly ejected from their fruits at high rates of speed. I remember learning about this in college: that dwarf mistletoe seeds can travel up to 60 mph and fly more than 60 feet from their hosts (Hinds et al., 1963). This process is triggered by internal heat production (called thermogenesis) within the mistletoe fruit — something that's never been observed in another plant (Rolena et al., 2015). It wasn't until many years after college that I actually experienced the phenomenon for myself. I remember driving along the Trinity River here in northern California and seeing a sudden splattering of little gelatinous green balls all over my windshield. I still remember how excited I was when I realized what they were: seeds that had flown as fast as I was driving.
Dwarf mistletoe fruits. Credit: Thompson Rivers University shared via Flickr Creative Commons.
It turns out that the seeds are only one of many intriguing things about mistletoe. There are more than 1,300 species of mistletoe; they grow all over the world (on all continents except Antarctica!); they support and interact with wildlife in all kinds of neat ways (Watson, 2001); and they are part of human culture and tradition (even evoking a kissing response in some!). And yet they're parasitic — not usually our favorite type of organism. More specifically, they're hemi-parasitic, meaning that they obtain all of their water and minerals from their host plant, but have some ability to provide for themselves. For example, leafy mistletoe, which is common in oaks where I live, is fully photosynthetic and therefore has a limited impact on its host trees. Dwarf mistletoe is a more demanding guest, requiring water, minerals and other nutrients, and taking a much greater toll on the many species of plants that it inhabits.
Leafy mistletoe is fully photosynthetic and therefore has a limited impact on its host trees. Credit: Dan Kidwell shared via Flickr Creative Commons.
As a major forest pathogen, dwarf mistletoe has a strong and well-studied connection to fire. Studies conducted in the 1970s clearly noted the relationship, pointing to fire suppression as the primary driver of increasing dwarf mistletoe abundance in many North American forests (Alexander and Hawksworth, 1975). At that time, dwarf mistletoe was recognized as one of the most damaging pathogens in many important forest types, and its impacts on the timber industry — with estimated losses of 3.2 billion board feet annually (Shea and Howard, 1969) — spurred quite a bit of research into its ecology and potential control tactics. Wildfire and prescribed fire naturally emerged as focal points for research, and those topics have continued to lure researchers, just as dwarf mistletoe has continued to wreak havoc. In a 2008 paper, Paul Hessburg and others argued that due to its wide distribution and habitat versatility, “dwarf mistletoes are probably responsible for more tree growth and mortality losses each year than all other forest pathogens combined.”
Like most forest pests and diseases, the relationship between fire and dwarf mistletoe is a two-way street: mistletoe affects fire, and fire affects mistletoe. For example, research has shown that mistletoe-infested stands of ponderosa pine have higher snag densities and higher fuel loads than uninfested stands, and that infested stands have higher crown fire potential (Hoffman et al., 2007). Mistletoe also has a number of tree-level effects that increase flammability and fire behavior potential, including the establishment of witches' brooms (dense, twiggy growth around areas of infection) and resinous stem cankers (Alexander and Hawksworth, 1975). Other research has documented reduced self-pruning and stunted growth in infected trees, both of which effectively lower the height of the live crown and thereby increase the potential for torching and canopy fire (Conklin and Geils, 2008).
The effects of mistletoe on fire behavior are fairly intuitive, but I find the effects of fire on mistletoe to be a little more intriguing. For instance, a study by Zimmerman and Laven tested the effect of smoke on the seed germination of three species of dwarf mistletoe, and they found that smoke exposure can reduce germination or prevent it altogether (when exposure exceeds 60 minutes) (1987). Earlier work by Koonce and Roth had also indicated that heat and smoke might have a disproportionate effect on dwarf mistletoe compared with their effects on the host plant (1980). Other studies have looked at the sanitizing effect that fire can have on mistletoe-infected trees. Conklin and Geils studied ponderosa pine stands in New Mexico, and they observed reductions in the dwarf mistletoe rating (DMR) — a categorical system for assessing infection (Hawksworth, 1977) — in 12 of 14 frequently burned plots (2008). This sanitizing effect was associated with average tree scorch above 25 percent, and it points to the potential utility of prescribed fire for dwarf mistletoe management, assuming that fire intensity is able to meet these minimum “scorch pruning” thresholds. Hessburg et al. also found that thinning and burning could be effective treatments for dwarf mistletoe in ponderosa and Douglas-fir forests, but that treatments would have to be implemented on regular intervals, as effects diminished after 20 years (2008).
Foresters using prescribed fire to treat mistletoe infestations in the 1970s. Credit: U.S. Department of Agriculture shared via Flickr Creative Commons.
Of course, the relationship between fire and mistletoe — and the approach to fire-based treatments — is highly dependent on the fire regime of the specific forest type in question. Much of the literature on dwarf mistletoe and fire comes out of frequent-fire forests like ponderosa pine and western mixed conifer, but lodgepole pine and black spruce are also common hosts, and their fire regimes are much different. In those types of forests, which are adapted to less frequent, more severe fire regimes, stand-replacing fire may be important for protecting future cohorts of trees from infection. Research in Rocky Mountain lodgepole pine forests showed that the time elapsed since the last stand-replacing fire was a good predictor of mistletoe infestation, and that the presence of remnant infected trees increased rates of infestation in younger, post-fire stands (Kipfmueller and Baker, 1998). In these forest types, the authors suggest that effective prescribed fire treatments would need to be intense and stand replacing.
I've always thought that mistletoe was interesting, but working on this blog opened a whole can of unexpected worms. Who knew that it was mistletoe, with its many interesting wildlife synergies, that inspired Charles Darwin to study evolution (Watson 2001)? Or that the term “mistletoe” is an ancient reference to some mistletoe species' reliance on seed dispersal by birds, who eat the seeds then deposit them on tree branches — the name comes from “misteltan,” an Anglo-Saxon word meaning “dung twig” (!!). Mistletoe has also been used by humans to bait deer for hunting (the foliage is quite tasty!); to treat infertility, syphilis, bubonic plague, epilepsy and other ailments; and to celebrate the return of summer, which mistletoe hints at with its evergreen foliage (Paine and Harrison, 1992). So with this blog, I celebrate mistletoe — i.e., dung twig, kissing plant, ballistic seeder, fire friend and foe — as quite possibly the coolest plant ever!
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Alexander, M. E., & Hawksworth, F. G. (1975). Wildland fires and dwarf mistletoes: a literature review of ecology and prescribed burning (Vol. 14). Rocky Mountain Forest and Range Experiment Station, Forest Service, US Department of Agriculture.
Hawksworth, F. G. (1977). The 6-class dwarf mistletoe rating system. The 6-class dwarf mistletoe rating system., (RM-48).
Hinds, T., Hawksworth, F. & McGinnies, W. Seed discharge in Arceuthobium: a photographic study. Science 140, 1236–1238 (1963).
Hoffman, C., Mathiasen, R., & Sieg, C. H. Dwarf mistletoe effects on fuel loadings in ponderosa pine forests in northern Arizona. Canadian Journal of Forest Research, 37, 662-670.
Kipfmueller, K. F., & Baker, W. L. (1998). Fires and dwarf mistletoe in a Rocky Mountain lodgepole pine ecosystem. Forest ecology and management, 108(1-2), 77-84.
Koonce, A. L., & Roth, L. F. (1980, April). The effects of prescribed burning on dwarf mistletoe in ponderosa pine. In Proceedings of the Sixth Conference on Fire and Forest Meteorology, Seattle, Wash (pp. 22-24).
Paine, L. K., & Harrison, H. C. (1992). Mistletoe: its role in horticulture and human life. HortTechnology, 2(3), 324-330.
Rolena, A. J., Paetkau, M., Ross, K. A., Godfrey, D. V., & Friedman, C. R. (2015). Thermogenesis-triggered seed dispersal in dwarf mistletoe. Nature communications, 6, 6262.
Shea, K. R., & Howard, B. (1969). Dwarf mistletoe control; a program for research and development in the West. West Forest Conserv Assoc West Reforest Coord Comm Proc.
Watson, D. M. (2001). Mistletoe—a keystone resource in forests and woodlands worldwide. Annual Review of Ecology and Systematics, 32(1), 219-249.
Zimmerman, G. T., & Laven, R. D. (1987). Effects of forest fuel smoke on dwarf mistletoe seed germination. The Great Basin Naturalist, 652-659.
Reposted from UC Agriculture and Natural Resources news
Although individual extreme weather events cannot yet be reliably linked to global climate change, the warming planet may be contributing to recent weather disasters in California. Across the state, 129 million trees died as a result of the drought of 2011-2016, many of them in the Sierra Nevada. Last fall, the worst wildfires in the state's history whipped through wildland areas and neighborhoods, and then were followed by a January deluge and deadly mudslide.
Climate change is also impacting agriculture. The winter chill that farmers rely on to re-boot cherry, pistachio, walnut and other important fruit and nut crops has been curbed by unseasonably warm nighttime temperatures. Sustained summertime heat waves are damaging crops and putting diminishing water resources under stress.
Climate change isn't just about the planet. Increased frequency and intensity of climate extremes impact peoples' lives by forcing evacuations and migration from fire- and flood-prone areas, reducing the availability and safety of food, and dampening emotional well-being.
How can Californians grapple with climate change?
On the front lines of climate change education, mitigation and adaptation is UC Cooperative Extension (UCCE), with its network of scientists headquartered throughout the state, living and working in communities where local climate change impacts must be addressed.
In 2015, UCCE's parent organization, UC Agriculture and Natural Resources (UC ANR), formed a Climate Change Program Team to lead a coordinated effort by UC ANR staff and academics dealing with climate change. The team surveyed UC ANR academics to find out about their current role in California climate change resilience.
“Eighty percent of respondents thought incorporating climate change impacts, mitigation and adaptation in their programs is important,” said UCCE specialist Ted Grantham, a member of the program team. “Less than half are actually doing so.”
The barriers respondents shared to working on climate change include technical complexity, lack of relevant information, and discomfort with the difficult conversations climate change can trigger. The program team brought together a diverse group of specialists, advisors and staff for a two-day workshop in February to increase capacity to raise public awareness about climate change, find practical ways to reduce the impacts of climate change, and help communities adapt to the reality of a changing planet.
Keynote speaker Michael Crimmins, a climate science extension specialist at the University of Arizona, said land-grant outreach programs have the interdisciplinary expertise and connections to provide decision support to farms and communities facing a warming world.
“Climate change is too big to tackle alone,” he said. “We have a lot of programs that can nibble at the edges. If everyone nibbled at the edge, we can make a difference.”
Resources are available for climate change extension
Myriad climate change resources were presented. UC Davis professor Arnold Bloom shared a free online college course posted at http://climatechangecourse.org. The course examines the factors responsible for climate change, the biological and social impacts, and the possible engineering, economic and legal solutions. Forty-eight mini-lectures, assignments and even exams are available to anyone willing to devote time to understanding climate change.
UCCE specialist Jeff Mitchell explained ongoing efforts to implement conservation agricultural practices on California row crop land. Research has shown the potential for climate change mitigation with precision irrigation and tillage reduction, practices that sequester carbon in the soil, reduce fertilizer needs, improve soil quality and increase yield.
Greg Ira, coordinator of the UC California Naturalist program, said a new advanced training module on climate stewardship is in development. The training will be provided to select certified California Naturalists, volunteers who work with partner organizations across the state on environmental stewardship, nature education and citizen science.
UCCE specialist Maggi Kelly introduced the website http://Cal-Adapt.org, which contains volumes of climate change projections and climate impact data from California's scientific community. Users can explore projected changes in temperature, precipitation, snowpack and sea level rise in California over this century with interactive climate data visualizations. They can download data, find peer-reviewed research and learn how to use climate projections.
Leslie Roche, UCCE rangeland management specialist, conducted rancher interviews after the 2011-2016 drought to gauge whether they consider climate change an important consideration for their ranching businesses, and whether they believe future climate will be different from the past. She found that ranchers are generally confident that they have the skills to manage for long-term drought, and that they are interested in learning about climate change and its potential impacts on their industry.
Roche has aggregated rangeland drought- and climate-management resources online at the Rangeland Drought Hub. The website includes “Voices from the Drought,” the personal stories of ranchers discussing the agonizing decisions they made during the drought – such as culling cattle, reducing staff, paying more for feed, and allocating limited water resources.
Steve Ostoja, the director of the USDA's California Climate Hub, said the program helps California farmers, ranchers, forest landowners and tribes maintain sustainable communities and ecosystems by adapting to climate variability and change. Guido Franco of the California Energy Commission said the organization recently released its fourth Climate Assessment. The assessment presents research on the impacts of climate change on the state, as well as strategies to dramatically reduce greenhouse gas emissions.
“I found the information and materials compiled by the Climate Change Program Team very useful,” Mitchell said. “I will be consciously using these in extension education when I can.”
UC California Institute for Water Resources academic coordinator Faith Kearns led a segment of the workshop on climate communication, taking into account the emotional side of climate change by practicing active listening and empathy building. She shared climate change communication strategies used by effective national advocates, such as Katherine Hayhoe, an evangelical Christian and climate scientist who recommends a soft approach that starts by establishing personal connections with individuals before diving into climate science.
Another approach is that of Sarah Myhre, a climate scientist at the University of Washington who believes scientists should speak boldly about climate change facts.
“… scientists are naturally risk-averse when it comes to public dialogue,” Myhre wrote in an essay on Guardian.com. “The verbal, argumentative skills common to professions in law, politics, or business do not come easily to most scientists. … Our job is not to objectively document the decline of Earth's biodiversity and humanity, so what does scientific leadership look like in this hot, dangerous world?”
At the meeting, UCCE advisor John Karlik pointed out that some listeners want to hear straight science, just facts.
“We're all needed,” Kearns said. “We all come with a difference set of circumstances and groups that we can connect with.”
The workshop closed with action planning and next steps. Among the needs presented during the session were:
- A climate change online portal with resources, tools and data that allow advisors and specialists to translate information into decision support.
- Simplified scientific information and case studies to personalize climate change impacts.
- Training for educators, advisors, specialists and volunteers.
- Research-based evidence on the impacts of climate change on food security and the cost of healthy food.
- A glossary of climate change terms.
In their article on the climate change survey in California Agriculture journal, the members of the UC ANR Climate Program Team said they believe UCCE is well positioned to understand and communicate the consequences of climate change to the public, and to identify strategies to mitigate negative outcomes for local economies, the environment and public health.
“UC ANR can become a powerful catalyst for climate adaptation and we should embrace a leadership role in advancing the knowledge and tools needed for a climate-resilient California,” they wrote.
Reposted from the Fire Adapted Communities Learning Network blog
Reposted from UC Berkeley's CNR News
In their announcement of the award, the Faculty Senate commended Gilless for being a “colleague of uncommon energy, commitment, and skill,” whose work “demonstrates exceptional devotion to the life and mission of the campus as a whole.” Gilless has been a professor of forest economics at Berkeley since 1983, and has served on a number of Senate committees including Academic Planning and Resource Allocation (1996-99), Educational Policy (2001-06), and Undergraduate Scholarships and Honors (1991-93, 1999). His deep involvement in the work of the Berkeley Division of the Faculty Senate demonstrates his commitment across a wide range of issues.
In addition to his service at Berkeley, Gilless has been a leader in committees across the UC system, including serving in the systemwide Academic Senate, the University Committee on Committees, and four years on the University Committee on Educational Policy.
In recognition of Gilless's accomplishments, former chair of the Berkeley Faculty Senate Division, Elizabeth Deakin, said, “Keith belongs to a group of faculty who are energetically engaged, seek to represent the welfare of the faculty as a whole, work hard to obtain and assess data on the issues, investigate the pros and cons of various viewpoints, develop expertise in the subject matter, find positive ways forward, and provide the leadership needed to see their ideas implemented in many cases. Keith has been a campus treasure.”
Champions of the Forests Researchers receive $2.5 million to study the effects of climate and climate change on trees along river channels
Riparian forests — the ribbons of trees that grow along river channels — play an important ecological role as refuges for endangered species in dry areas. But these natural havens are increasingly threatened by the changing frequency and intensity of drought, both of which are byproducts of climate change.
Scientists at UC Santa Barbara are studying how riparian forests respond to climate change that manifests as hotter and drier conditions over time. With $2.5 million in combined funding from three grants, Michael Singer, a researcher with UCSB's Earth Research Institute (ERI), and colleagues seek to understand the impact of nonstationary climate — trends in temperatures and precipitation — on riparian forests.
“As a river starts drying up, groundwater-dependent trees like those in a riparian forest might disappear, or the moisture within the soil might dry up, affecting more shallowly rooted trees and shrubs,” explained Singer, who also is a lecturer at Cardiff University in the United Kingdom.
Through the National Science Foundation's Geography and Spatial Sciences Program, one project — led by associate professor John Stella of the State University of New York College of Environmental Science and Forestry (SUNY-ESF) — is being conducted near UCSB in Ventura County's Santa Clara River Valley. A basin with competing water needs — ecological, urban and agricultural — the Santa Clara, because it goes dry, relies largely on subsurface groundwater. Continual pumping of groundwater from the aquifer for agriculture, when that aquifer is not recharged by rainfall, causes wells to go dry and forces pumping efforts to reach deeper and deeper.
Innovative new legislation in California, the Sustainable Groundwater Management Act (SGMA), shifts the management of groundwater resources from the state to local basins, requiring regional stakeholders to create action plans for managing water resources. With the grant, Singer and Stella will collaborate with UCSB geography professor Dar Roberts and The Nature Conservancy to develop an improved understanding of forest health along the Santa Clara River. They'll investigate matters including what happens to trees that are rooted at depths below the surface with diminishing groundwater, and their findings can be used to administer SGMA.
Through another NSF grant, in its Hydrologic Sciences Program, Singer, Stella and ERI director Kelly Caylor, also a professor in UCSB's Bren School of Environmental Science & Management, will study riparian forests along a major European river. The Rhône, which flows through France from Lake Geneva to the Mediterranean Sea, warms 2 degrees Celsius along its climate gradient. The researchers plan to measure the variation in temperature, precipitation and climate to model what might happen under climate change and determine how water availability to forests shifts due to climate and how trees are using water, as well as their corresponding growth and health outcomes over time.
The scientists also will core trees to determine their age and will extract cellulose from individual rings for isotopic analysis. Oxygen isotopes are used to distinguish water sources such as groundwater or rainfall, while carbon isotopes reveal how efficiently trees are using that water — a calculation of photosynthesis versus water loss.
The third project is funded by the Department of Defense through the Strategic Environmental Research and Development Program. Singer, Stella, Roberts and Caylor will develop a toolkit and provide quantitative support for land and water conservation management to promote the sustainability and resilience of riparian forest ecosystems located on DOD lands. The endeavor focuses on three dry area bases in drought-prone regions: Vandenberg Air Force Base near Lompoc; Marine Corps Base Camp Pendleton in San Diego County; and the driest, U.S. Army Fort Huachuca in southeastern Arizona.
“In all of these studies, we're developing water stress indicators, which can be physical manifestations such as dropping leaves or branches or trees becoming less green,” Singer explained. “Such markers can be seen in remote sensing imagery and tree-ring isotopes, but we're also looking at climate records for precipitation and temperature, along with numerical modeling to determine what type and how much water has been delivered to a basin in the first place. If we see trends that tell us the forest is really suffering, we hope to establish an early warning response window in which managers can act quickly before important patches of forests are lost.
“Combined, those various metrics give us a good idea of how well trees are doing,” Singer added. “We hope to integrate the results of these projects to eventually predict the thresholds of species collapse and perhaps even forest collapse. If we can identify what the dominant controls on those thresholds are climatically, we may be able to assess whether trends in temperature are more relevant than those for precipitation.”