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Oak (Quercus spp.)

White Oak ; leaf | Stillwater, MN

Oak are probably one of the most prominent, distinguished, and easily recognizable family of trees in Minnesota. All native Oaks have sinused leaves, and all produce acorns. They are hardy, widespread, and long lived (most living up to 150 years). Next to the Cottonwood and the Eastern Pine, Oaks are the tallest trees in the state. They are wonderful shade producers, and provide either food or shelter for much of Minnesota's diverse wildlife, including Deer, Squirrels, Chipmunks, Heron, Egrets, Woodpeckers, Grouse, Turkeys, Chickadees, Nuthatches, Blue Jays, and countless others, and their wood supplies valuable nutrients for funguses and the soil.

Oaks reproduce by way of acorns, a fruit that is very popular with much of Minnesota's wildlife. Unfortunately, they're not like the seeds of Mountain Ash or Choke Cherry trees; their seeds are specially designed to go through the digestive tracts of birds and other animals -- it actually helps the trees to spread! When a squirrel eats an acorn, it's gone. That's why there aren't as many Oaks as there are Aspens and Cherry trees, which is just as well. Quaking Aspens may spring up quickly, but they don't have the longest lifespan. Oaks have long lifespans, and are generally the trees that form the upper canopy of the forest. They've also evolved, over thousands of years, to stagger the amount of acorns they produce every year. This is a kind of population control, meant to curb the resident acorn-eating population so that they won't grow so large as to eat an entire acorn crop. Some mammals, like the squirrel and the chipmunk, will bury caches of acorns in the ground. While they often dig them up in the winter, some are almost always left behind, helping to sustain new forest growth.

There are six varieties of Oak in Minnesota; the Northern Pin Oak, White Oak, Swamp White Oak, Bur Oak, Black Oak and Red Oak. Each is best suited to slightly different conditions.

The leaves are usually the easiest way to tell one Oak from another, but sometimes people get confused when we talk about the sinuses (gaps) and lobes (tips). We've provided a simple illustration below.

Black Oak (Quercus velutina):The Black Oak produces short, wide, yellowish acorns with thin, scaley caps that are very bitter. When first budding, its leaves are red, then greyish, eventually turn a dark green. When mature, they have wide sinuses and the lobes have sharp points, and turn a dull orange in the fall. Its bark is grey and not as furrowed as other members of the oak family.

Bur Oak (Quercus macrocarpa):The Bur Oak is the largest Oak in Minnesota. It is also the most easily identifiable; just look for the "burry" cap that covers all but the very tip of the brown nut. The acorns are edible, and actually very tasty if you can find one without a grub in it. Its leaves have rounded lobes, with sinuses that are deep at the base, and shallow at the crown. The second sinus is usually pretty pronounced, which makes it a bit easier to distinguish from the White Oak. Its thick, furrowed, corny grey bark, is resistant to fires. Its leaves are usually yellow at the peak of fall, fading slowly to brown as winter approaches.

Northern Pin Oak (Quercus ellipsoidalis): The Northern Pin Oak prefers dry soil, and can often be found growing on hillsides. Its acorns stay green for an entire year, and only turn brown in the fall of the second year. When mature, the Acorns are pretty much what you'd see in your average textbook or encyclopedia; brown nuts with slightly darker caps that cover the bottom third of the nut. The acorns are edible, but contain a toxin called tannic acid, which can be fatal in large doses. It has deep furrows, with pointed tips that curve slightly upwards at the edges. The bark is grey with rather shallow furrows.The leaves turn a deep crimson in the fall.

Northern Red Oak (Quercus rubra): The Red Oak is fairly distinguishable from other Oaks if you look closely. Its leaves are rather fat, and have shallow sinuses and pointed lobes. Its acorns are short, and often flat on top. They don't taste the best, and aren't as popular with squirrels and other wildlife as other species of Oak are. It is fairly hardy, and can survive well in most soils. The leaves turn red in the fall.

Swamp White Oak (Quercus bicolor): The acorns of the Swamp White Oak look a little like those of the Bur Oak, but the spurs along the cap are shorter, and the acorns themselves are fatter, and not nearly as pointed. The leaves are a much better and more reliable way to tell the two apart, as the sinuses are very shallow, and almost indistinguishable at the crown of the leaf. The bark is grey and furrowed. Its leaves turn a rusty brown in the fall.

White Oak (Quercus alba): Like the Northern Pin Oak, the White Oak produces fairly textbook-shaped acorns; brown nuts with slightly darker caps that cover the bottom third of the nut. The acorns are edible, though you should boil them first, as they contain tannic acid, a toxin which can be fatal if enough is ingested. The leaves are an easy way to tell the White Oak apart from the Pin Oak. The sinuses are fairly prominent, and the lobes are rounded.

Multimedia:

Northern Pin Oak; leaf and acorn | Stillwater, MN	Red Oak ; leaf | Stillwater, MN	White Oak; leaf | Stillwater, MN
Northern Pin Oak; bark | Stillwater, MN	Bur Oak ; bark | Woodbury, MN	White Oak; bark | Stillwater, MN
Northern Pin Oak; spring profile| Stillwater, MN	Northern Pin Oak; summer profile| Stillwater, MN	White oak ; summer profile| Stillwater, MN

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