Bearing no fruit

Heading to and from Chico State, Mark Stemen regularly passes a cherry tree planted to memorialize John Bidwell’s orchard. That land, bequeathed by the city’s founder in 1887, became what’s now the university; trees with map markers denote corner boundaries, including the venerable cherry by the campus-entrance side of Laxson Auditorum.

Last week, between rain showers, Stemen stopped his bike at the tree. He gently grasped a branch and inspected the buds. Unlike neighboring flora, the cherry had no blossoms.

“Bidwell’s orchard wouldn’t grow today,” remarked Stemen, a Chico State professor and chair of the city’s Sustainability Task Force. “And he wouldn’t recognize the weather.”

Fruit trees, nut trees—of varieties old and new—along with other staples of North State agriculture have become affected by shifting conditions connected to climate change. A recent study from scientists across multiple University of California campuses, including UC Davis, details “consequent impact on crop yields … and agricultural vulnerability to climate risks.”

That report (titled “Climate Change Trends and Impacts on California Agriculture,” published Feb. 26 in the journal Agronomy) meshes with work Stemen has undertaken with former student Molly Marcussen, a CivicSpark fellow assigned jointly to Chico and Butte County. Using data and forecasting models from state-authorized software CalAdapt, along with analysis from Stemen’s students, Marcussen is preparing climate vulnerability assessments for both the city and county that will set the stage for climate adaptation measures required under state law.

These findings don’t just involve growers and governments.

They hit home for anyone with a garden—or a fruit tree.

Stemen planted a cherry tree in his mother’s front yard around four years ago. This year, he wanted to put in a plum. He realized, however, he couldn’t select any varietal in the nursery section of any store and expect it to bear fruit by the time it’d mature. He went to Hodge’s Nursery in Durham, where he found a Santa Rosa plum instead of the Burgundy plum he’d initially eyed for aesthetics.

Even more striking, as the statewide climate changes, entire types of fruits and nuts “will no longer be viable,” Stemen explained. “For example, cherries: It’s estimated that by 2040, there will be no more place available to grow cherries. Or pears. Or apples.

“Almonds probably aren’t going to be affected; but stone fruits—like peaches, nectarines, plums—are going to be problematic, and another crop that falls into that same category is walnuts.”

Thinking back to the cherry tree he planted, a Rainier variety, Stemen added: “The [UC] study points out, and I even realize this, that people are making 10- to 25-year investments here. It’s going to take 10 years for my cherry tree to ever get to being a big, producing cherry tree, and by then it won’t work.”

The change in climate most Californians notice is heat, which can hurt some crops. For fruit and nut trees, though, cold is the more significant problem.

At issue is the cumulative total of chilling hours, time spent below 45 degrees. Stemen pointed to the study’s summation that “the lack of adequate chilling hours can delay pollination and foliation,” or the emergence of leaves, and result in “reduced fruit set and poor fruit quality.” Walnuts and pistachios have male and female flowers whose synchronized timing “is regulated by the number of chilling hours.”

Around 1950, chilling hours in the Sacramento Valley ranged between 700 and 1,200 per winter, depending on the spot. During the past four years, chilling hours have fallen below 500. That’s fine for almonds and olives, which need just 200—but not for stone fruits and walnuts (700) nor apples and cherries (1,000-plus) over the long haul.

Marc Walsh, a physical scientist who’s been forecasting for Chico-based Western Weather Group since 1989, said his firm’s agricultural clients have noticed the recent years’ trend. In fact, it’s been evident to anyone who’s observed that Tule fog no longer is a routine occurrence.

“By just that phenomenon alone, I’d say there were more chilling hours 10 to 20 years ago than there are now,” Walsh said by phone. Although dry years, such as the mid-2000s and 2011-15, and urban development are factors, “1 or 2 degrees can make a difference in the fog formation in the valley.”

That trend will continue, based on forecasting from CalAdapt and other models in the UC study.

Ken Hodge, who owns Hodge’s Nursery, said by phone that he’s seen the difference chilling hours make, even year to year. Cherries have been “hit and miss” recently; “the previous winter we had lots of chilling hours and cherries bore like I’ve never seen before,” but other years have had “mild winters and we won’t have enough chilling hours to trigger the fruit buds.”

A nuance such as chilling hours, he said, “most people don’t think about.”

Yet chill—and heat—have ripple effects. Eye-opening effects.

“If you know that’s what’s happening in your garden,” Stemen said, “imagine what’s happening in the California garden.”