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Too Warm To Grow Tree Crops? Farmers Work To Temper Climate Change Effects

Ezra David Romero
Valley Public Radio
Tom Coleman's crews are working across the region to prune pistachios trees before buds set in.

The valley’s fruit and nut trees need cold temperatures in the winter in order to go to sleep and wake up healthy in the spring. New research suggests that in as little as 30 years, it may be too warm in the valley to grow these trees due to climate change. Valley Public Radio’s Ezra David Romero reports that the agriculture industry is taking the issue very seriously.

Tom Coleman is busy pruning branches off pistachio trees that aren’t budding at an orchard just north of Fresno in Madera County. He farms and manages more than 8,000 acres of pistachios across the state.

"This is something that could impact a lot of farmers. . . and in fact it's already impacting farmers on random given years across the state." - David Doll, UCANR

“Here’s an example of some hanging down nuts from last year that just wouldn’t come off because of the position on the tree so we want to remove that,” says Coleman.

Coleman’s worried these trees won’t get enough sleep this winter. Crops like pistachios, peaches and almonds need a certain amount of cold weather every year. This is what the agricultural industry refers to as chill hours.

Frigid temperatures between 32 and 45 degrees help set buds that in the spring will turn into flowers and then in summer into fruit and nuts. The problem is there’s a decrease in the amount of hours growing areas actually reach these temperatures. Coleman’s trees need to get more than 700 hours of sleep every winter, but for the past four years many have routinely slept less than 500 hours.  

“And as result of that they do not bloom uniformly and when they don’t have uniform bloom it can dramatically reduce the yield of the field,” says Coleman.

Credit Eric Leudeling
Safe winter chill in California's Central Valley in 1950, 2000, 2041–2060 and 2080–2099, calculated with the Chilling Hours Model.

This is a problem that farmers are facing across California and consumers should care because if this keeps happening prices for these products could go up. Predictions from multiple University of California studies say that within 30 to 50 years it may be too warm to grow many tree crops where they flourish today.

In EikeLeudeling's research he found that climate conditions in California by "the middle to the end of the 21stcentury will no longer support some of the main tree crops currently grown" here. He adds that those who grow tree crops will either need to find alternative crops to grow or establish ways to mitigate warming temperatures.

One UC Davis researcher recently published a study in the peer-reviewed journal California Agriculture. In Hyunok Lee’s studyshe found that winter temperatures are increasing more than any other time of year. Her modeling looks at the year 2050 in Yolo County.

“Our agriculture will continue,” Lee says. “But if you look at . . . like 20 years or 30 years. The pattern may change a little bit, crops may move a little bit north.”

"I know that there are people that think that global warming is not man-made, but regardless we have to deal with it. I think that making plans around it are necessary." - Tom Coleman, Pistachio Grower

Credit File Photo / Creative Commons/g.h.vandoorn
Creative Commons/g.h.vandoorn

She says tree crops like walnuts would be harmed the most and that annual crops like tomatoes could benefit if temperatures keep rising. This is all a big deal for growers with huge investments in the ground with trees that have life cycles of 25 years or more. 

Merced County UCANR Farm Advisor David Doll is trying a number of things to get the trees more sleep like using overhead sprinklers above the trees and even painting them white with liquid clay to reflect sunlight.

“So this is something that could impact a lot of farmers over the next 10, 20, 30 to 40 years,” Doll says. “And in fact it’s already impacting farmers on random given years across the state.”

Credit David Doll / UCANR
UCANR Farm Adviser David Doll paints pistachio trees white with liquid clay to reflect sunlight. This in turn cools the trees.

This problem is so prevalent that climate change deniers really can’t get away from it. Crops have failed because of warming temperatures. (Doll explains more about chill hours here.)

In 2015 the California pistachio industry was hit hard by a lack of chill hours. As a result the crop was nearly split in half. The UC system and the pistachio industry have invested about a million dollars to figure out a way around warming temperatures. Kern County UCANR Farm Advisor Craig Kallsen is trying to breed a pistachio tree that needs less sleep.

“We’re trying to use the other species of pistachios actually to see if we can come up with something that has a low chill requirement. It’s pretty hypothetical at this stage,” Kallsen says. “We made quite a few crosses this spring and we actually hope to put a trial in a low chill area.”

It’s not just pistachio trees that aren’t getting enough shuteye. Kern County Farmer Steve Murraysays his cherries may suffer this year due to a warmer winter.

"Initially it was looking like 2017 was going to be a disastrous year because not only were the trees not getting chilling, but they were actually heating up." - Steve Murray, Cherry Farmer

“Initially it was looking like 2017 was going to be a disastrous year because not only were the trees not getting chilling, but they were actually heating up,” Murray says. “When the sun hits the wood – the temperature of the wood can be 20 and even 30 degrees warmer.”

Murray says the only real way to fix this problem is for the temperature to drop. And to complicate the matter even more all the researchers and farmers I spoke with say there isn’t enough known about why the trees need sleep to understand it all. Plus, a decrease in the amount fog in the region is also a factor in why the trees aren’t staying cool. That has to do with rain.

Back on Tom Coleman’s plot of 160 acres of pistachios it’s rained so much that a large creek has formed in the middle of his property.  He’s hoping the ground is saturated enough that fog forms this winter lowering the temperature around his trees.

Credit Ezra David Romero / Valley Public Radio
Valley Public Radio
Tom Coleman hopes all the rain increases fog levels around his orchards.

“The fog is a good thing because it keeps a little more uniform cooler temperature on the ground, but we just haven’t seen that over that last several years even with the rain,” says Coleman.

For Coleman the facts are evident. The climate is warming and he has to adapt his practices.  

“I know that there are people that think that global warming is not manmade, but regardless we have to deal with it. I think that making plans around it are necessary,” says Coleman.

These tree’s that he’s prided himself on since the 70s could live well beyond him and his children.  He’s taking warming temperatures seriously, because what happens with the climate today could mean severe cuts or total crop loss in the coming decades.  

Ezra David Romero is an award-winning radio reporter and producer. His stories have run on Morning Edition, Morning Edition Saturday, Morning Edition Sunday, All Things Considered, Here & Now, The Salt, Latino USA, KQED, KALW, Harvest Public Radio, etc.
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