The idea seemed too crazy to Rod Simmons, a measured, careful field botanist. Naturalists in Arlington County couldn’t find any acorns. None. No hickory nuts, either. Then he went out to look for himself. He came up with nothing. Nothing crunched underfoot. Nothing hit him on the head.
Then calls started coming in about crazy squirrels. Starving, skinny squirrels eating garbage, inhaling bird feed, greedily demolishing pumpkins. Squirrels boldly scampering into the road. And a lot more calls about squirrel roadkill.
The absence of acorns could have something to do with the weather, Simmons thought.
To find out, Simmons and Arlington naturalists began calling around. A naturalist in Maryland found no acorns on an Audubon nature walk there. Ditto for Fairfax, Falls Church, Charles County, even as far away as Pennsylvania. There are no acorns falling from the majestic oaks in Arlington National Cemetery.
Simmons has a theory about the wet and dry cycles. But many skeptics say oaks in other regions are producing plenty of acorns, and the acorn bust here is nothing more than the extreme of a natural boom-and-bust cycle. But the bottom line is that no one really knows.
A word about the mighty oak. Long before people paved over the area, much of the Washington region was covered by oak and hickory forests. There are at least 20 different species of oak trees in the region, and they produce acorns on different cycles: white oaks every year and red oaks every two years. Each tree, too, has its own two- to four-year cycle, producing many acorns one year and few in other years. Stressed trees, including those trying to survive extended drought conditions in the Washington region, often wildly overproduce acorns to ensure the survival of the species.
Oaks are one of the few trees that can self-pollinate and “clone” themselves. But they prefer the genetic variety that comes from the flowers of male trees pollinating the flowers of female trees. That’s a dance that takes place every spring, usually in May, for anywhere from seven days to two weeks, depending on the weather.
And the weather is critical. A late frost can kill the flowers and any chance of pollination. But there was no late frost in this area last year, according to the National Weather Service. Gypsy moths and other insects can damage trees, but because the pollen is airborne, insects don’t play much of a role in oak reproduction.
That leaves Simmons’s theory. Last spring was so wet, he reasoned, perhaps the pollen was washed out of the air and down storm drains before it had time to do its work.
Ed Zimmer, regional forester for the Virginia Department of Forestry, doesn’t buy that.
But last May, when the oak trees would have been busy flowering, coating cars and sidewalks with a thick dusting of golden pollen, the National Weather Service logged 10.6 inches of rain at Reagan National Airport — three times the normal amount, making it the third wettest month on record since 1871.
Whatever the reason for no acorns, foresters and botanists are paying attention.
But they say they’re not worried yet. “What’s there to worry about?” said Alan Whittemire, a botanist at the U.S. Arboretum. “If you’re a squirrel, it’s a big worry. But it’s no problem for the oak tree. They live a long time. They’ll produce acorns again when they’re ready to.”
White oaks can live as long as 300 years. Faster-growing red oaks can reach 200. And it takes only one acorn to make a tree, he said, which in an urban area with little open space is often more than enough.
“This is probably just a low year, a biological event, and it’ll go away,” Zimmer said. “But if this were to continue another two, three, four years, you might have to ask yourself what’s going on, whether it is an indication of something bigger.”
– from washingtonpost. 30 Nov 2008