A boon for the arts and crafts set and a pitfall for joggers, pine cones galore seem to be littering streets, sidewalks, and yards this spring.
The bumper crop of crunchy cones was three years in the making, said Peter Del Tredici, senior research scientist at the Arnold Arboretum.
The cones were formed in the fall of 2007 and pollinated the following spring. They expanded to their present average size of about six inches last year. And in September, they shed their seeds. The spent cones are finding their way to the ground now.
“They’re falling right now because the twigs are starting to expand,” Del Tredici said. “As the twigs fill with sap, the cones get pushed off.”
The increase in spent cones is not unusual, he said. White pine trees exhibit a phenomenon known as "mast seeding."
Mast seeding trees produce a small amount of seeds every year. Every three to seven years, however, they yield a heavy crop.
In the case of white pines, that results in an explosion of fallen crunchiness.
“What’s really interesting is that this behavior is synchronized over a relatively large geographic area,” Del Tredici said. “In southern New England, for example, all of the pine trees are going to have heavy crops of cones at the same time. So then the question becomes, what are the factors that cause this synchrony? And that’s a very hard question to answer.”
Botanists have examined the way weather impacts seed production in white pines, but it seems to play little role, Del Tredici said.
Studies of other mast seeding trees, such as oaks -- which produce huge numbers of acorns some years and smaller crops others -- have found that the irregular cycle may be an evolutionary strategy, Del Tredici said.
The irregularity means that some years squirrels and other rodents feast and others they famish, so their populations don't grow too large and ravage the trees.
“Predators can’t adapt to reproduction on an irregular cycle,” Del Tredici said.
Although the theory hasn’t been proven for white pines, the good news for those tired of raking fallen cones is that the trees aren’t expected to produce another big crop of cones for several years.
“The fact that you have to go out there and rake up these cones might be annoying, but all trees are messy,” Del Tredici said.
“And, hey,” he added, “it doesn’t happen very often.”
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