If global warming projections hold up, tree crops that rely on the 'winter chill' in California's Central Valley could be in peril, say researchers in a new study. If you aren't aware, California's Central Valley fields produce 25 percent of America’s table food, which seems like a big responsibility for a state that is below Romania in world standing in the eyes of financiers who gauge whether or not a government can pay its bills.
The study is the first to map winter chill projections for all of California, which is home to nearly 3 million acres of fruit and nut trees that require chilling. The combined production value of these crops was $7.8 billion in 2007, according to the California Department of Food and Agriculture.
Overview of California's Central Valley, showing the distribution of orchards that require winter chill, the major producing counties and the subdivisions of the Central Valley analyzed separately in this study. PLoS ONE 4(7): e6166. doi:10.1371/journal.pone.0006166
Why is winter chill important?
Most fruit and nut trees from non-tropical locations avoid cold injury in the winter by losing their leaves in the fall and entering a dormant state that lasts through late fall and winter.
In order to break dormancy and resume growth, the trees must receive a certain amount of winter chill, traditionally expressed as the number of winter chilling hours between 32 and 45 degrees Fahrenheit. Each species or cultivar is assumed to have a specific chilling requirement, which needs to be fulfilled every winter.
Insufficient winter chill plays havoc with flowering time, which is particularly critical for trees such as walnuts and pistachios that depend on male and female flowering occurring at the same time to ensure pollination and a normal yield.
"Depending on the pace of winter chill decline, the consequences for California's fruit and nut industries could be devastating," said Minghua Zhang, a professor of environmental and resource science at UC Davis.
So what is the solution, since wind farms will likely be as useless as they have always been and Californians won't accept the science behind nuclear power?
"Our findings suggest that California's fruit and nut industry will need to develop new tree cultivars with reduced chilling requirements and new management strategies for breaking dormancy in years of insufficient winter chill," said Eike Luedeling, a postdoctoral fellow in UC Davis' Department of Plant Sciences.
Fruit and nut growers commonly use established mathematical models to select tree varieties whose winter chill requirements match conditions of their local area but obviously if those conditions change, tree varieties may have to change also.
To provide projections of winter chill, the researchers used hourly and daily temperature records from 1950 and 2000, as well as 18 climate scenarios projected for later in the 21st century. They then introduced the concept of "safe winter chill," the amount of chilling that can be safely expected in 90 percent of all years. Using those combined hypotheses they calculated the amount of safe winter chill for each scenario and also quantified the change in area of a safe winter chill for certain crop species.
The researchers found that in all the scenarios they used in their models, the winter chill in California declined substantially over time. Their analysis in the Central Valley, where most of the state's fruit and nut production is located, found that between 1950 and 2000, winter chill had already declined by up to 30 percent in some regions.
Using data from climate models developed for the Intergovernmental Panel on Climate Change Fourth Assessment Report (2007), the researchers projected that winter chill will have declined from the 1950 baseline by as much as 60 percent by the middle of this century and by up to 80 percent by the end of the century.
Their findings say that already by year 2000 winter chill had already declined to the point that only 4 percent of the Central Valley was still suitable for growing apples, cherries and pears — trees which have high demand for winter chill.
The researchers further project that by the end of the 21st century, the Central Valley might no longer be suitable for growing walnuts, pistachios, peaches, apricots, plums and cherries.
"The effects will be felt by growers of many crops, especially those who specialize in producing high-chill species and varieties," Luedeling said. "We expect almost all tree crops to be affected by these changes, with almonds and pomegranates likely to be impacted the least because they have low winter chill requirements."
The research team noted that growers may be able change some orchard management practices involving planting density, pruning and irrigation to alleviate the decline in winter chill. Another option would be transitioning to different tree species or varieties that do not demand as much winter chill.
There are also agricultural chemicals that can be used to partially make up for the lack of sufficient chilling in many crops, such as cherries. A better understanding of the physiological and genetic basis of plant dormancy, which is still relatively poorly understood, might point to additional strategies to manage tree dormancy, which will help growers cope with the agro-climatic challenges that lie ahead, the researchers suggested.
Citation: Luedeling E, Zhang M, Girvetz EH (2009) Climatic Changes Lead to Declining Winter Chill for Fruit and Nut Trees in California during 1950–2099. PLoS ONE 4(7): e6166. doi:10.1371/journal.pone.0006166
- PHYSICAL SCIENCES
- EARTH SCIENCES
- LIFE SCIENCES
- SOCIAL SCIENCES
Subscribe to the newsletter
Stay in touch with the scientific world!
Know Science And Want To Write?
- Schrödinger's Cat Is Not Just Alive And Dead, He's Both In 2 Places At Once
- Case For Moon: Humanity's Gateway To The Solar System - Open Ended Exploration With Planetary Protection At Its Heart
- Mindfulness Is Not A Waste Of Time
- B0 Meson Lifetime Difference Measured By ATLAS
- Voluntary Birth Control To Stop Climate Change - Or Else
- Arctic Ocean Methane Does Not Reach The Atmosphere
- We’re Not In Europe Any More: BfR Statement On EDCs Embraces The Risk-Based Approach
- "this must be mystery, Cat Mystery. lol..."
- "Vampire are not real, and can never be. This stuff is limited to movies only...."
- "Milk is so tasty. Soy, Oy! CO2 is fertilizer for plants. We need more of it. Meat is tasty too..."
- "Both the Pacific Salmon Forum and the Cohen Commission agree there is scant evidence farming salmon..."
- "If interested in an electromagnetic model of the photon structure and its absorption process, as..."
- The Name Game: How Unethical Environmental Groups and Toxic Fanatics Scare You With Words
- Naturopathy: A Pre-holiday Rant
- Misdiagnosis of Dehydration in Older Folks
- The Amazing Things Poo Can Tell Us About Health
- This Dinner Plate Sucks—Literally
- Gwynn’s Appeal to Jury Could Overshadow Medical Science
- New meta-analysis shows ketamine effective against persistent post-surgical pain and could provide major cost-savings globally
- Refusing access to surgery recovery area at a UK hospital unless WHO Safe Surgery Checklist is fully complete
- Investment in energy storage vital if renewables to achieve full potential
- The Lancet Oncology: Teenagers and young adults still fare worse than children for many common cancers, according to Europe-wide
- Coping with active surveillance anxiety in prostate cancer