Climate Change Made Me Do It

A sapsucker stretches after its winter arrival at the Dipper Ranch orchard.
This one looks like a cross between the red-naped sapsucker and the red-breasted sapsucker.  

Me in October:

Hardly any walnuts have fallen on the ground at the Dipper Ranch and they're all pecked open by birds. There will be no walnut harvest party this year.  It must be the four-year drought. The walnut trees leafed out in June this year - two months late. It must be climate change.

 The Dipper Ranch walnut trees in December:

Here's a few thousand walnuts on the ground for you. Sorry, dropped them in their husks this year. And it's going to rain soon so you better pick them up before they mold. Isn't climate always changing?

It's easy to blame everything on global climate change. The new "dog-ate-my-homework" excuse. But even before the changes to the earth's atmosphere as a result of human industrial development, California had a lot of fluctuation in its weather from year to year. Its climate is largely influenced by the shifting of a high pressure system over the northern Pacific Ocean, fluctuations in ocean surface temperatures, and the many versions of interplay between them. Were the Dipper trees so late in breaking bud and dropping walnuts this year in response to one of the natural oscillations in California's weather?

A modest but delicious harvest from two English walnut trees in 2015.
Notice the series of pecked holes in the bark of these walnut trees - made by sapsuckers.   

We don't irrigate the two English walnut trees behind the barn. They seem to survive the dry summers on whatever rain they get in the winter. Like most orchard trees, they have a big crop one year followed by a small crop the next year. The handsome trees are over fifty years old, so they survived the 1976-77 and the 1987-92 California droughts.

The 2011-2015 California drought is possibly the most severe in our state in 1200 years. By studying tree-ring chronology of blue oaks and other environmental indicators, scientists believe there have been longer periods of droughts and other three-year periods with less precipitation in California, but  the record high temperatures of recent years combined with the lack of precipitation caused very low soil moisture levels, a great stress on plants (Griffin and Anchukaitis, 2014).

Some scientists are now saying that higher temperatures of human-induced climate change may have contributed to this recent California drought (Williams, et al, 2015):

"Precipitation is the primary driver of drought variability but anthropogenic warming is estimated to have accounted for 8-27% of the observed drought anomaly in 2012-2014 and 5-18% in 2014.  Although natural variability dominates, anthropogenic warming has substantially increased the overall likelihood of extreme California droughts."

Scrubbing the sodden husks off the walnuts.   

In most years, I just pick a handy date between Halloween and Thanksgiving, invite a bunch of friends, and we have a walnut harvest party. Dipper Ranch walnuts are exceptionally good-tasting, but the harvest party is as much about celebrating the upcoming rainy season, eating pie and watching the sunset as it is about collecting walnuts off the ground. Even if they can't come to the party, certain people get a bag of walnuts on their desk or doorstep every year to keep me in their good graces. So canceling the traditional harvest party this year was a big deal.

Drying the walnuts   

In 2015, because the walnut ripening cycle was so late, December storms were knocking the walnuts to the ground still in their husks rather than the husks splitting open on the tree and dropping wooden-shelled nuts one-by-one to the ground in the dry weather of early October. With the surprise late drop of walnuts, there wasn't time to organize a party. To save the harvest I was picking up walnuts after work in the winter dark and gathering them in the rain. I immediately rubbed off the soggy brown husks and rushed the mess into the house for an agitated rinse in the sink and then an hour of drying in the oven so the walnut meat inside the shells would not mold. Even though I was wearing gloves while harvesting and processing the nuts, the dark husks soaked through and stained my fingertips. I went to many a holiday party hiding my hands. But all the work was worth it because this year's crop is delicious and it gave me time to think about California's wet-dry weather and climate change.

A red-breasted sapsucker waiting for rain.   

It was the sapsuckers that really got me thinking about climate change. This year and every year, certain woodpeckers and sapsuckers show up at the Dipper Ranch in November or December. My first clue to their arrival is the squeaky call of the red-breasted sapsucker. Then I start seeing downy woodpeckers, Nuttall's woodpeckers and even red-naped sapsuckers in the orchard trees. These winter visitors join the resident red-shafted flickers, acorn woodpeckers and scrub jays and Steller jays feasting on the persimmons and walnuts but usually not until after my walnut harvest party. In most years the birds get a few walnuts which I don't begrudge, but never before had I found such big piles of pecked walnuts falling from the trees. What was going on?

In the coast range, we've seen signs of plants responding to this most recent drought: less germination of the annual plants, earlier onset of blooming and summer dormancy, and more dead trees. The US Forest Service mapped 27 million trees which have died in California's forests in this current drought, and other scientists have detected 58 million large trees experiencing severe canopy water losses indicating stress that could result in future tree death or forest changes over 2.5 million acres in California (Ashner 2016).

Zaggy zebra-stripes across the entire back = Nuttall's woodpecker.   

Migratory birds move around and are not as immediately susceptible to fixed conditions such as soil moisture in their winter range. This year when the sapsuckers arrived on their regular November schedule, there were still plenty of walnuts hanging in the tree where they prefer to sample them and they benefited from the shift in walnut ripening. But if the orchard trees eventually die, the sapsuckers may stop visiting the Dipper farmyard every winter.

Mango the cat wonders what these walnuts are doing in his territory.  

Whether the Dipper Ranch walnut harvest this year was affected by natural cycles, human-induced climate change or both, it's not that hard for me and my fellow walnut enthusiasts to adjust. But sometimes something insignificant but personal, like canceling a party, gets you thinking about the bigger picture. Plants and animals won't be able to shift in response to climate changes at the same rate together. Plants will be more susceptible at first since they can't move. Animals that can travel long distances may be able to find substitute niches for a time. But the longstanding ecological dependencies between plants and animals will change and new patterns will have to emerge.

As Margaret Atwood says it, "It's Not Climate Change - It's Everything Change." Although she is describing the social impacts of climate change on a global scale, the recent California drought is mentioned twice in her cleverly illustrated article.

Now that the 2015 Dipper Ranch walnut harvest is in, you know what the next step is, right? The annual Dipper Ranch walnut label contest. Coming up soon. I hope you like snakes.

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D. Griffin and K. J. Anchukaitis, 2014, How Unusual is the 2012-2014 California Drought?, Geophysical Research Letters, 41, 9017-9023.

A. Williams, A.P.R. Seager, J.T. Abatzoglou, B.I. Cook, J.E. Smerdon, and E. R. Cook, 2015, Contribution of Anthropogenic Warming to California Drought During 2012-2014, Geophysical Research Letters, 42, 6819-6828.

Gregory P. Asner, Philip G. Brodrick, Christopher B. Anderson, Nicholas Vaughn, David E. Knapp, and Roberta E. Martin, 2016,  Progressive forest canopy water loss during the 2012–2015 California drought, Proceedings of the National Academy of Sciences 113: E249-E255.

Margaret Atwood, July 27, 2015, It's Not Climate Change - It's Everything Change.

Some other California climate change sources:

Climate News Archive, California Department of Water Resources
Climate of California, Western Regional Climate Center
Indicators of Climate Change in California - Report Summary, California Office of Environmental Health Hazard, August 2013
California's Most Significant Droughts: Comparing Historical and Recent Conditions, California Department of Water Resources, February 2015.
Tens of Millions of Trees in Danger From California Drought, The Carnegie Airborne Observatory.