A Glimpse of Nature — Oaks: Some ID & Ecology

The foundation of nature study is the habit of watching and wondering, of making observations and asking questions, a habit that I try to practice daily and to encourage through this blog. These simple, and sometimes brief, observations quickly point to the complexity of our world.

In writing A Glimpse of Nature, I hope to demonstrate the joys and accessibility of nature study AND to focus attention on some of those complexities. As unwise as it may be to combine both, here I go again. Let’s start with the visible.

Last week’s “homework” was to gather several different oak leaves and acorns. The oak genus, Quercus, is divided into two major groups: the red oak group and the white oak group. Species in each group share some common characteristics. The most obvious difference is that the lobes on red oak leaves terminate in bristles, which the leaves of white oaks lack. Hence, species in the red group look pointy; those in the white group appear rounded.

Red Oak Group White Oak Group

This can be observed even in young plants like those pictured below.

Red Oak Group White Oak Group

With a little practice, the difference can be seen overhead.

Red Oak Group

White Oak Group

White Oak Group

In southeastern Massachusetts, there are several species in each group. The “reds” include black oak, scarlet oak, red oak, pin oak, and bear oak (scrub oak). The major “whites” are white oak and swamp white oak. The species within these groups display a wide variety of leaf shapes.

Now examine those leaves that you collected last week. Do they belong to the red or the white group? Recognizing the correct group narrows down the possible species. Other characteristics to notice include the shape of the lobes and sinuses, that is, the gaps between the lobes; the presence of hairs on the underside; and the overall leaf shape. To learn how to identify our local oak species, I would suggest either The Sibley Guide to Trees or an online resource such as the USDA’s “Field Guide to Native Oak Species of Eastern North America” . . . and lots of practice.

As with any organism, it is useful to notice your oak tree’s habitat. Is it growing on upland or in a wetland? What kind of soil does it prefer? Is it growing at the top or bottom of a hill . . . or somewhere in between? Are there any signs of fire, grazing, lumbering, etc.? Gathering such information can be useful in identifying a species and in seeing how it fits into its plant community.

As for acorns, those in the red oak group have thin, flat scales that overlap like the bracts of an artichoke. The thicker scales of white oak acorns look bumpy in comparison.

Red Oak Group

White Oak Group

When examining acorns, consider their size and shape. Are they spherical or oval? Is the cup bowl-shaped or shallow? How much of the nut does the cup cover? Is the inside of the cup smooth or velvety?

The acorns of trees in the white oak group mature within one year, drop in autumn, and sprout. You won’t find acorns on their branches during winter. In contrast, the acorns of trees in the red oak group require two growing seasons to mature. Immature nuts can be found on their branches in winter, and the fallen nuts wait until spring to germinate.

If you are bold, another difference can be observed through taste. The meat of white oak acorns is mild; that of red oaks is quite bitter. Not surprisingly, mammals favor the tastier nuts of the white oak group. A tiny sample, or even touching your tongue to the raw meat, will distinguish the two. If you wish to cook with acorns, they will require processing with boiling water to remove those bitter tannins.

The challenge posed by such a taste test is finding a fresh, undamaged nut. Earlier this evening, I thought I’d repeat the taste comparison, so I dipped into the small stash of acorns that I’d brought home from recent walks. I knew they would be dried out, but I wasn’t making a meal of them. The acorn from the scarlet oak was dry, hard and bitter -- just as expected. The white oak acorn, on the other hand, was disintegrating and occupied by a chubby white grub. [Lower left in the photo.]

This is not at all unusual. Here are a few more random acorns from my collection:

Holes, chew marks, and insect damage are the norm. I learned this long ago as I collected acorns for children’s crafts. And, I should add, that this “damage” is for the best: it is evidence of a vibrant forest that supports many life forms.

A National Geographic article entitled “Life in a Nutshell” describes the miniature ecosystem that thrives in living and dead acorns. The “Field Guide” below can be magnified within the linked article. After reading the article, it will be hard to view acorns as inanimate objects. The article also succeeds beautifully in shifting the reader away from a human perspective and scale.

Moffett, Mark W. "Life in a Nutshell." National Geographic Magazine, vol. 175, no. 6, June 1989, pp. 783+. National Geographic Archive 1888-1994, tinyurl.gale.com/tinyurl/DtpEH4. Accessed 16 Nov. 2021.

We’ve all seen squirrels collecting and burying acorns, but their use of these nuts reveals just the tip of the herbivory iceberg. Black bears, white-tailed deer, wood ducks, ruffed grouse, blue jays, white-footed mice, meadow voles, chipmunks, and raccoons are among the 96 users cited in American Wildlife & Plants: A Guide to Wildlife Food Habits. Some of these animals depend upon acorns for their survival. Yes, this requires an enormous amount of acorns, but oak trees provide. According to the New York Botanical Garden’s “Gardening FAQ” column, “One huge oak can drop up to 10,000 acorns in a mast year!” Only a small percentage of these need to escape herbivores in order to ensure the next oak generation.

Moreover, acorns are just one food that oaks provide wildlife, albeit the one that looks most edible to humans. By far, the largest group of organisms supported by oak trees is insects, who feed on the tree’s roots, sap, and above all else, its leaves. Indeed, few oak leaves escape the impacts of hungry herbivores and decomposers.

Yet, through their capacity to photosynthesize, the large, long-lived oaks support not only their own needs, they also create food that sustains much of the forest’s fauna and fungi. As Doug Tallamy so eloquently explains in The Nature of Oaks: The Rich Ecology of Our Most Essential Trees, the vast array of insects that depend on oaks become, in turn, nutritious food for insectivorous birds and for baby songbirds. This “bird food” cannot survive without their trees. Bear this in mind the next time someone tries to sell you a “pest-free plant” or offers to solve your “insect problem.” Native plants and the insects that evolved with them keep the whole ecosystem functioning.

Future posts will explore some of these ecological relationships and pay further homage to the grand oaks.