If Spring had a royal crest it would surely depict buds bursting, squawking nestlings, and a rainbowy wreath of wildflowers. Absent would surely be acorns. But to the wise (and ravenous) gray squirrels, acorns are as indelibly a part of spring as they are fall.
Squirrel droppings
Every spring, the trails in Centennial Woods are littered with small clippings of red and black oak twigs bearing long tassels of flowers and 5-10 of the delicate nascent green leaves. Under a single mature Northern red oak, I’ve counted over 100 of these twigs laying about. The twigs generally have clean cuts at about 45°, and there’s no obvious sign that any leaves have been removed and all the male catkins (the tassels) are still intact.
When I first noticed this spring phenomenon, my suspicion was that squirrels might be clipping twigs to build out their dreys (they raise their litters in these nests; breeding typically happens twice each year, once in January and again in June). But even a few weeks after twigs start showing up on the forest floor, it’s clear that the squirrels aren’t coming back to collect them. So whatever the squirrels are doing up at the top of the tree, it’s clear that the twigs are just the discarded scraps. Curiously the cut twigs show up only under red oaks and not white oaks, an indication of a key underlying ecological difference between the two groups of oaks.
Red vs White Oak
Somewhere between the rank of genus (Quercus for oaks) and species is the taxonomic rank of “sections.” Our Vermont oaks fall into one of two sections: red oaks (Lobatae) and white oaks (Quercus). The distinction is quite clear when looking at the leaves (leaf guide): red oaks (e.g. Northern red, black, and pin oak) have bristles at the tips of their lobes while the lobes of white oaks (bur, white, and swamp white oak) are rounded.
The distinction between the sections is harder to see in the acorns, but the difference in how they develop is quite different. White oak flowers are pollinated in the spring and develop into acorns that both drop and shortly after germinate in the fall. All the acorns on a white oak tree are roughly the same age and therefore the same size. Same is true for the acorns that drop in the fall, same age, same size. Because their acorns germinate in the fall they don’t have to endure an entire winter hoping not to get eaten by squirrels or worry about decomposers breaking down their protective shell. As a result, white oak acorns have lower concentrations of tannins.
While red oak flowers are also pollinated in the spring, their acorns take two full growing seasons to develop. A single red oak twig, then, can have two different age and size classes during the spring and summer. Many of the first year acorns are aborted during the growing season and fall off in the fall so you find acorns big and small under red oaks. And where white oak acorns germinate in the fall shortly after dropping, red oak acorns don’t germinate until the spring after they fall. The pollinated flowers from this spring will drop as acorns in the fall of 2025 and germinate in the spring of 2026.
This also means that red oak twigs at this time of year have tiny, half-formed acorns dotting their twigs (these are the acorns that began growing in the spring of 2023). And because these acorns are not yet fully formed, they’re not yet worth fully defended yet (tannin concentrations are significantly lower in these young acorns than they will be in the fall. The squirrels take advantage of the helpless acorns, pruning off the twig, eating the young acorns and then dropping the twigs to the forest floor!
