Dec 14, 2016

Drought strikes centuries-old California oaks

Pepperwood Preserve Rd, Santa Rosa, CA
USA
by
Kathleen Wong
,
Phys.org
While forests at all three study sites (Pepperwood Preserve to the north, Blue Oak Ranch, and Canyon Ranch to the south) showed signs of water stress by August 2015, the leaf canopy of trees held progressively less water the further south they were. Photo: Todd Dawson
While forests at all three study sites (Pepperwood Preserve to the north, Blue Oak Ranch, and Canyon Ranch to the south) showed signs of water stress by August 2015, the leaf canopy of trees held progressively less water the further south they were. Photo: Todd Dawson

The most severe drought in living memory did a number on California's blue oaks. A new study by UC Berkeley researchers shows how even centuries-old trees struggled when landscape water disappeared between 2012 and 2015.

Some showed stress by producing miniature leaves, some by shedding leaves, and some simply died.

...

Two species of trees, valley oaks (Quercus lobata) and blue oaks (Quercus douglasii), produced striking responses. The changes were easiest to see in their leaves. The first year of severe drought, the blue oaks at the driest southern site produced freakishly shrunken leaves. Normal blue oak leaves are about the length of a human thumb. At Canyon Ranch, the foliage of the most water-stressed trees was the size of a pinky fingernail.