It’s Been a “Nutty” Season of Acorns
There are several folktales when it comes to forecasting the severity of winter weather, and one I have heard quite a bit this fall is, this winter will be severe because oak trees are producing so many acorns. Recent hikes in our woods have been more like skating on ball bearings than leisurely saunters among the oaks. Southern New England is rich in oak trees of various species, and this year the hopeful progeny of these oaks litter the forest floor.
NASA’s Landsat Satellite Imagery in 2006 indicate our region is 67 percent forested land with 50 percent represented by deciduous species of trees, notably oak, hickory, maple, and birch. The balance is conifers, such as white pine and eastern hemlock, at 12 percent and 5 percent in forested wetlands. Around here a year with an abundance of acorns is hard to miss, especially for hikers in our oak-filled deciduous forests and for homeowners doing their fall cleanups that might include thousands of acorns. Those familiar with trees refer to a year of acorns as a “hard mast year” and we certainly have it this year. Mast is the botanical name for nuts, seeds, or fruits of trees and shrubs that are a food source for wildlife. Hard mast includes nuts and seeds like acorns and hickory nuts and soft mast includes berries and fruit.
I have always been fascinated by oak trees. The yard and neighborhood where I grew up was full of large red oaks. In my pre-teen years my playground included a tree house my dad had constructed, or I should say he started, and I finished. He attached a sheet of heavy plywood to a couple of two-by-fours nailed to a red oak “triple trunk” that had sprouted from a single stump. I took it from there, using the plywood dad had attached as a roof and upper deck, adding a lower section with walls, and requisitioning an old tin milk bottle container for a seat. I added a ladder to the top deck and a second ladder to a lookout roost in the tallest upper branch. It was my hideout, where along with my imagination, I was joined by the many creatures calling my tree home. Most were insects traveling bark highways and hiding among crevices from hungry chickadees and nuthatches. Blue jays would call from upper branches and the occasional squirrel would stop by.
Now, well into my 6th decade, my youthful life among oaks has matured with my job as Chief Ranger of The Last Green Valley National Heritage Corridor. I have been looking into the biological meaning and significance of a heavy mast year for oak trees and share what I have learned from various reliable sources.
An excellent book on trees is “Woods Whys: An Exploration of Forests and Forestry,” by Michael Snyder. In his chapter “Does a Bumper Crop of Acorns Predict a Harsh Winter,” he writes:
“Ecologists have speculated – and put forth supporting data – that masting is adaptive reproductive strategy. The so called ‘predator satiation’ idea holds that trees starve would-be seed predators during lean years and overwhelm them with seed during bumper years. The lean years keep the populations of seed-eating insects, mammals, and birds low enough that when a bumper seed year comes along, the predators cannot eat all the seeds, so an excess is available for regeneration of trees.”
My newest and favorite book on oak trees is “The Nature of Oaks: The Rich Ecology of Our Most Essential Native Trees,” by Douglas W. Tallamy. In his section on masting, he includes two additional reasons for the occasional abundance of acorns.
“A second explanation for oak masting has nothing to do with outpacing acorn predators. There is evidence that masting evolved to improve pollination. Oaks within particular taxonomic lineages may synchronize their reproductive effort to maximize pollination efficiency. For the most, oaks are wind-pollinated, and wind pollinated plants, not surprisingly, are at the mercy of the vagaries of wind. Simple probability statistics tell that pollination success will increase if there is more pollen blowing around when the female flowers on oaks are mature and open. Synchronizing the release of pollen in some years, therefore, results in lots of successful pollination and mast crop of acorns.”
“There is yet a third hypothesis that offers an explanation for masting in oaks, and it has to do with energy allocation. In most years there are not enough resources (water, nutrients, and sunlight) to produce the energy required for oaks to both grow and make a lot of acorns all at the same time. Making acorns requires a great deal of energy, so during mast years oaks grow very little. This is evident if you closely examine oak growth rings after the fact. Accordingly, the energy allocation hypothesis suggests that oaks partition available energy; some years they allocate it to growth, other years they direct energy toward reproduction.”
Tallamy goes on to suggest that like many ecological explanations, the three hypotheses about oak masting are not mutually exclusive. What better explanation than our oaks survive and thrive by evolving strategies that include allocating limited resources, flooding the zone with acorns to outpace predators and synchronizing pollination efficiency.
Oaks are all around us and provide crucial home and habitat to countless creatures – including tree house escapes for children like me. The more we explore the outdoors, take time to go slow and see more, search out scholarly driven answers to the mysteries of nature, then the more we’ll come to appreciate our place in the world right outside our doorstep.
We live in a beautiful place called The Last Green Valley. We are blessed to live within such a wooded landscape full of oaks, and this October, many, many acorns. I hope you’ll join me and others as we enjoy it, care for it, and pass it on.
Additional information for this column comes from the essay by David Mance III, “Mast Mysteries” in “The Outside Story, Volume 2,” published by Northern Woodlands, and “Oak the Frame of Civilization,” by William Bryant Logan.
Bill Reid is the Chief Ranger of The Last Green Valley National Heritage Corridor. He can be reached at 860-774-3300 or email at Bill@tlgv.org
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