- Author: Julie Singer
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.”
- Author: Kat Kerlin
Reposted from UC Davis News
As climate change transforms California's landscape in the years to come, coastal habitats appear to be more resilient than many other places in the state. (Getty Images)
Current levels of greenhouse gas emissions are putting nearly half of California's natural vegetation at risk from climate stress, with transformative implications for the state's landscape and the people and animals that depend on it, according to a study led by the University of California, Davis. However, cutting emissions so that global temperatures increase by no more than 2 degrees Celsius (3.2 degrees Fahrenheit) could reduce those impacts by half, with about a quarter of the state's natural vegetation affected.
The study, published in the journal Ecosphere, asks: What are the implications for the state's vegetation under a business-as-usual emissions strategy, where temperatures increase up to 4.5 degrees Celsius by 2100, compared to meeting targets outlined in the Paris climate agreement that limit warming to 2 degrees Celsius?
“At current rates of emissions, about 45-56 percent of all the natural vegetation in the state is at risk, or from 61,190 to 75,866 square miles,” said lead author James Thorne, a research scientist with the Department of Environmental Science and Policy at UC Davis. “If we reduce the rate to Paris accord targets, those numbers are lowered to between 21 and 28 percent of the lands at climatic risk.”
The report notes that this is a conservative estimate because it only examines direct climate exposure. It does not include increased wildfire or insect attacks on forests, which are also intensifying and likely to increase with further warming. These secondary effects are likely to have large impacts, as well, the authors say. For example, during the recent drought, more than 127 million trees died primarily due to beetle outbreaks, and wildfires have consumed extensive amounts of natural vegetation.
68 percent of LA, San Diego regions impacted
The study features maps of the state and shows the climate risk to 30 different vegetation types under different climate scenarios. It projects that at current rates of greenhouse gas emissions, vegetation in southwestern California, the Central Valley and Sierra Nevada mountains becomes more than 50 percent impacted by 2100, including 68 percent of the lands surrounding Los Angeles and San Diego.
“This is the map of where we live,” Thorne said. “The natural landscapes that make up California provide the water, clean air and other natural benefits for all the people who live here. They provide the sanctuary for California's high biodiversity that is globally ranked. This map portrays the level of climate risk to all of those things. In some cases, the transformation may be quite dramatic and visible, as is the case with wildfire and beetle outbreaks. In other cases, it might not be dramatically visible but will have impacts, nevertheless.”
Resilient areas also identified
The study and its maps are being used by state agencies and land managers to make decisions under changing conditions. Commissioned by the California Department of Fish and Wildlife, the data is helping the agency understand not only which parts of the state are vulnerable to climate change, but also which areas are more resilient, such as some coastal areas and parts of northwestern California, so they can ensure they remain resilient.
“In California, we have good information on the vulnerability of fish and wildlife to climate change,” said Whitney Albright, a project manager with the California Department of Fish and Wildlife. “But we were missing this crucial piece of climate risks to underlying habitat. This study helped fill the information gap. We've already started to use its data in our conservation planning efforts.”
The study also provides a risk assessment for policymakers to consider the benefits to California of reaching Paris climate agreement emission targets that limit global warming to 2 degrees Celsius, and the risks to the state of remaining on the current business-as-usual level of emissions and temperature warming.
Co-authoring institutions included the California Department of Fish and Wildlife, Sequoia and Kings Canyon National Parks, and the U.S. Geological Survey.
The study was funded by the U.S. National Park Service and the California Department of Fish and Wildlife./h2>/h2>/figcaption>
- Author: Jeannette Warnert
Reposted from the UCANR Green Blog
UC Cooperative Extension researchers convey need for more climate change communication and curriculum tools
Reducing greenhouse gas emissions from natural and working lands is one of California's key climate change strategies. In particular, the potential for farm and rangeland soils to serve as carbon sinks has been getting a lot of attention lately in the national media — and during California Healthy Soils week, which wrapped up Dec. 7.
These are areas where UC Cooperative Extension, with its local presence across the state, is well-positioned to drive change. But as a recent survey of UCCE advisors, specialists and faculty found, while there is a good deal of climate work happening, there are also some significant obstacles.
The survey results — reported in an article by UCCE academics Ted Grantham, Faith Kearns, Susie Kocher, Leslie Roche and Tapan Pathak in the latest issue of California Agriculture — showed that while nearly 90 percent of respondents believe it is important to incorporate climate science into extension programming, only 43 percent currently do so.
Respondents pointed to a number of issues. One was "limited familiarity with climate science fundamentals." It's one thing to cite the overwhelming scientific consensus that climate change is real and is being driven largely by human activity; it is another to be able to respond quickly and convincingly to detailed questions from doubters. This list from Grist, for instance, details more than 100 common arguments raised by climate skeptics, many of which have non-trivially complex answers.
Another important issue cited by respondents was "fear of alienating clientele by talking about a contentious topic," a response that highlights the importance of personal relationships in UCCE's work, and the challenge of communicating an area of science that is highly politicized.
The authors conclude: "To further increase the capacity of UC ANR staff to support the needs of their clientele and the broader public, professional development around climate science fundamentals, communication, and adaptation strategies is critical." As an initial follow-up, the UCANR climate change program team (led by authors Grantham, Kocher and Pathak) is presenting a workshop and professional development meeting for extension professionals in February.
For more from California Agriculture, the research journal of UCANR, see the full issue with articles on mapping soil salinity in the San Joaquin Valley via satellite; choosing forage seed mixes for rangeland restoration; growing oilseeds in winter without irrigation; keeping dairy cows cool in the summer; breeding better carrots; and more.
- Author: Jason Alvarez. University Communications
Reposted from UC Merced News
Yosemite Valley in the western Sierra Nevada Mountains.
What if nature were to become a polluter, discharging millions of tons of planet-warming carbon into the atmosphere in much the same way as diesel-fueled trucks or coal-fired power plants?
This nature-as-polluter scenario might seem far-fetched, but it's well on its way to becoming reality, according to a recent study co-authored by UC Merced Professor LeRoy Westerling.
In a paper published recently in Scientific Reports Opens a New Window.— “Potential decline in carbon carrying capacity under projected climate-wildfire interactions in the Sierra Nevada” — Westerling and collaborators from the University of New Mexico and Penn State University used three climate models and data from the Intergovernmental Panel on Climate Change to examine how rising global temperatures and increasingly severe wildfires will affect Sierra Nevada forests.
Their conclusion: Changing conditions will turn today's Sierra Nevada forests into tomorrow's greenhouse gas emitters.
“Forests play an important part in regulating the levels of atmospheric carbon,” Westerling explained. “Forests are carbon sinks, essentially giant stockpiles of carbon. Forests are also active carbon consumers. They remove carbon dioxide from the air and convert it into biomass. This traps the carbon, which is no longer free to act as a greenhouse gas in Earth's atmosphere.”
Professor LeRoy Westerling
But projections from Westerling and colleagues suggest that this may change. According to their models, Sierra Nevada forests will experience both a dramatic loss of stored carbon and a substantial decline in their ability to remove CO2 from the atmosphere.
Rising temperatures are creating a warmer, drier Sierra Nevada climate. Westerling previously showed that these changes are leading to dramatic increases in the frequency, size and duration of wildfires. The new study suggests that these same changes will make it harder for forests to regenerate, leading to a loss of forest density, with plants better suited to the new climate eventually replacing trees.
“As trees are displaced, the Sierra Nevada will lose its ability to sequester carbon,” Westerling explained. “The plants that spring up in their place will be significantly smaller, making them less effective carbon sinks than the trees they replaced.”
But the carbon stored in forest trees has to go somewhere.
As trees are burned in more frequent wildfires, and as dead trees undergo decomposition, Westerling and his colleagues predict that as much as 73 percent of the carbon in Sierra Nevada forests will be released, resulting in a dramatic spike in atmospheric carbon. This will transform the Sierra Nevada from a carbon sink into a carbon emitter, making the nature-as-polluter scenario a reality.
Westerling and his collaborators note that their predictions are actually conservative. The effects might be more extreme than their models suggest.
“Our study does not account for a number of factors that might influence the dynamics of forest carbon,” Westerling said. “However, the factors we ignored are likely to accelerate the loss of forest. Our predictions likely underestimate the severity of actual effects.”
Though the predictions are alarming, the authors remain optimistic, hopeful that their findings can contribute to a larger conversation about environmental policy and promote avenues of research that lead to sustainable forest management.
- Author: Jeannette Warnert
Reposted from the UCANR Green Blog
To help California forest property owners adapt to the changing climate, UC Agriculture and Natural Resources (UC ANR) has produced a 13-page peer-reviewed paper that outlines actions owners can take to sustain their forests' value even when temperatures rise.
“Managers of forest land have always had to adapt to changing conditions – such as markets, urban encroachment, droughts and floods,” said Susie Kocher, UC Cooperative Extension forestry and natural resources advisor. “We wrote this paper to help forest managers better understand the evolving science of climate change and how they can help their forests adapt to the climate of the future.”
Forests are shaped by the climates in which they grow. The current rapid pace of climate change has not happened for thousands of years, according to climate scientists. Nevertheless, the authors assure forest landowners that there are land management decisions they can make to ensure the resiliency of their resources, and perhaps even improve them.
“Some trees may grow faster under the warmer conditions we experience with climate change,” Kocher said, “especially those at highest elevation where there is adequate precipitation.”
The paper details the solid scientific evidence that indicates the rise in global average temperatures over the past 100 years. The temperatures, it says, “will likely continue to rise in the future, with impacts on natural and human systems.”
The document provides specific recommendations for care of three common types of forest in California: mixed conifer, oak woodland and coastal redwood forests.
Mixed conifer forests – typically composed of white fir, sugar pine, ponderosa pine, incense cedar and California black oak – are susceptible to moisture stress caused by warmer temperatures and reduced snow and rain. The drier conditions make the trees more vulnerable to fire and insect attack.
The drought of 2010-2016 has already had a substantial impact on mixed conifer forests in the Sierra Nevada. Aerial detection surveys show that more than 102 million trees have died since 2010; more than 62 million died in 2016 alone.
The UC ANR climate change adaptation paper suggests reducing competition for water by thinning trees and managing for species and structural diversity. The authors suggest property owners consider the source of seedlings when planting new trees.
“Select seedlings adapted to a slightly lower elevation or latitude than your property,” Kocher said. “These would be more likely to thrive under the 3- to 5-degree warmer temperatures we expect in 50 years or so.”
Oak woodlands are widely distributed and diverse in California, which gives them moderate to high capacity to adapt to climate change. Mature oaks are more resilient than young trees and seedlings.
One potential impact of climate change on oak woodlands is increasing precipitation variability and increasing spring rains. The moisture change could increase the spread and prevalence of Sudden Oak Death (SOD), a disease caused by a bacterium that was introduced into California from outside the U.S. SOD is primarily a concern in areas with tanoaks in Central to Northern California coastal areas.
“To reduce the spread of sudden oak death, land owners should prevent the movement of infected leaves, wood and soil,” according to the paper.
The primary concern for coastal redwood forests is the decline in fog. Fog frequency in coastal redwoods is 33 percent lower now compared to the early 20th Century. Less fog and rain plus warmer temperatures would leave coastal areas where redwoods typically thrive drier. But that doesn't mean redwoods will disappear. Areas with deep soil and areas close to streams and rivers may provide refuge for redwood forests.
The new publication, Adapting Forests to Climate Change, can be downloaded free from the UC ANR Catalog. It is the 25th in the Forest Stewardship series, developed to help forest landowners in California learn how to manage their land. It was written by Adrienne Marshall, a doctoral student at the University of Idaho; Susie Kocher, UC Cooperative Extension forestry and natural resources advisor; Amber Kerr, postdoctoral scholar with the UC John Muir Institute of the Environment; and Peter Stine, U.S. Forest Service.