Good Seed Year for White Pine Trees

Wendy Scribner, UNH Cooperative Extension

Over the past few months, I have been noticing an abundance of white pine cones in the trees around Carroll county. Rather than producing consistent crops of seeds every year, white pine has good seed years every three to five years, with fewer seeds produced in the intervening years.

It takes two years for white pine cones to develop and mature. At the end of the first growing season, the cones will be approximately one inch long and a purplish color. During the second summer, the cones turn yellowish-green and then a light brown in the fall as they ripen. If you look up in the trees now, you will see many green cones that resemble "gherkin" pickles. The cones will open as they become mature and the seeds will be released in the fall, traveling anywhere from 200 to 700 feet from the tree.

Because white pine is an important timber species in New Hampshire, foresters are often trying to encourage white pine to regenerate following a timber harvest. Harvesting will often be timed with a good seed year to create the sunlight and soil conditions favorable to new pine growth. Shelterwood harvesting, where overstory trees are removed in a series of harvests over time, are frequently used to provide enough sunlight to establish the new white pine seedlings but not too much sunlight, which would favor the growth of sun-loving tree species. Harvesting activity is also used to "scarify" the soil which improves the opportunity for good seed germination. White pine establishes well on moist, mineral soil so the harvesting equipment action of mixing the mineral soil and leaf litter can help to prepare an ideal seedbed.

For centuries, white pine has been an important and valuable forest product grown for manufacturing here in New Hampshire. Once important for use as masts on sailing ships and later for boxes, our white pine is now valued for interior millwork, paneling and moldings. Pine forests also provide valuable habitat for a variety of our wildlife species. White pine seeds are eaten by a variety of bird species including nuthatches, crossbills, pine siskins and evening grosbeaks, as well as chipmunks, squirrels and other rodents.

So why do we have good and bad seed years? Producing flowers, pollen and seeds takes a tremendous amount of energy. When trees put energy toward seed production, they are diverting that energy from other life functions, thus they do not tend to have several years in a row of heavy seed production. Prolific seed years, when many trees are all collectively producing a lot of seed in a given year, seem to be related to environmental factors. This is an important strategy. If trees produced the same amount of seed every year, the populations of birds, rodents and other wildlife that feed on those seeds would reach population levels where they would consistently consume that seed, and thus very little would be available to germinate and grow into new trees. Periodically inundating the area with seed will overwhelm the seed predators and increase the potential for some seed to germinate.

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