Walt Koenig

ScienceShot: Oak Trees Listen to the Weather

Trees that produce huge fruit crops one year and none the next can also show spot-on timing, even when far apart: Among valley oaks (shown here) and blue oaks, individual trees separated by hundreds of kilometers often have simultaneous acorn booms and busts. But what kicks off this synchronized acorn extravaganza? To find out whether environmental conditions or wind-borne pollen are key, researchers made annual acorn-counting pilgrimages to 12 sites ringing California's Central Valley. They matched acorn tallies with temperature and rainfall records. In the current issue of Ecology, they found both species of oaks bearing bumper acorn crops in the same week or two during boom years, even when trees were more than 600 kilometers apart. That's too far for pollen to travel reliably. Instead, the researchers found, when it comes to oaks matching their acorn output, weather during springtime flowering seemed to be key.

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