– By Tom Worthley, UCONN Cooperative Extension
I hate to admit it, but I’ve been mowing down a lot of oak trees this summer. When you think about the difficulty we have, what with the deer and all, keeping oaks in the woodlot, you’d wonder why I’d do such a thing. Well, its not because I’ve become a cut-and-run timber bandit, in fact, I’m not even talking about timber-sized trees. The trees I’m talking about aren’t falling victim to my chain saw or axe, I’m literally mowing them with my lawn mower!
What I’m talking about is the abundant crop of oak seedlings that have germinated from the tree-mendous volume of acorns that came down at my place last fall. They’re coming up in the lawn, the garden, the driveway, the cracks in the walkway, the compost pile and every other darn place you look! I know I’m not the only one who experienced such a huge crop of acorns, either. Whenever I mention acorns recently people chuckle, roll their eyes, and launch into descriptions of the bushel baskets-full, the need to wear a hardhat outdoors, or walking around on ball-bearings and marbles last fall.
After dutifully blowing the leaves off the yard last autumn, I still had thousands of acorns stuck in the grass, pushed down into the soil, and jammed in the treads of my Vibram soles. I think I was shoveling acorns up along with the first snow! And now, all those acorns that didn’t get eaten by turkeys, squirrels, deer, bluejays and chipmunks have sprouted into little trees. The chipmunks got a lot of ‘em, too, bless their little hearts. Why, they’re so fat a couple of them even got caught by my old one-eyed dog. Anyway, the seedlings are quite abundant and I can’t help mowing some of them if I want to keep any lawn at all. It’s easy to see how quickly it would all go back to forest if I didn’t keep mowing it.
So why the great abundance of acorns last year? It’s not always like that. I checked into some of the silvical (ecological characteristics of trees) references to look for some answers.
The first thing I found was that among the oaks that are most common in our area, even among trees of the same species in the same stand, some individual trees are going to be more prolific seed producers than others. Also, abundant seed crops are cyclical. Even trees that normally produce abundant acorn crops don’t do so every year, and here is where it begins to get complicated. The cycle, or period between abundant crops of acorns varies dramatically from species to species. For example, black oak is reported to produce abundant acorns every 2-3 years, while chestnut oak produces a few every year, but in great abundance only every 4-5 years. White oak can take as long as 10 or as few as five years between good seed years. Red and scarlet oak are less reliable than black oak in that they may take as many as five years between abundant seed crops.
Weather in the spring can also play a role in acorn production. White and chestnut oaks produce acorns that ripen during the same growing season they are produced, and germinate in the fall soon after they drop. A warm week or so in the early spring when flowers form (about the same time that leaves appear), followed by cooler than normal temperatures when pollination takes place will almost guarantee an abundant seed crop regardless of the cycle on these species. I seem to recall warm and very dry conditions in the early spring of 2002, so that may be a factor.
Species in the “Red Oak Group” (red, black and scarlet) on the other hand, require two growing seasons for the acorns to ripen and fall. Even then, the acorns overwinter under a light layer of leaf litter and germinate the following spring. So weather conditions two springs previously may also be a factor. Acorns that must wait until spring to germinate are more susceptible to predation by mice, squirrels, insects, birds, etc., and in poor seed years 90 to 100% of the acorn crop may be consumed by wildlife.
This article originally appeared in the September 2003 ECFLA/WDLT Newsletter.