Flora and fauna of the Athens County area, and occasionally habitats outside Ohio. Subject matter will consist of both interpretive material and taxonomic issues in plant and animal identification.

Thursday, December 22, 2011

Oaks of Ohio

Oaks are one of the largest groups of woody plants in Ohio. I will not discuss every last species found in the state, but concentrate on 11 of the most common. Before we dive into the species, let's see what makes up an oak tree.

Oaks are known for their fruit, commonly called acorns.  They are partially covered by a cap or cup. These are examples of Ohio species, and one California Live Oak, the long rifle bullet shaped nut. The white oak group have bumpy or warty scales on their caps, and the red oaks have flat scales looking more like snake skin. The white oaks produce acorns every year, while the red oaks take two years to mature. Acorns are edible, but you want to boil out the bitter tannins first. White Oaks are sweeter tasting, but both groups are important to wildlife.

If the tree is too small to produce acorns, you can still identify it as an oak. Most types of trees have a single bud at the tip of each twig. Oaks have multiple buds clustered around the end of each branch.

Oaks have both male and female flowers on the same tree. The female portions are very small and found scattered on the branches. These are male flowers dangling down in a catkin like form. The flowers are bland, and not important in identifying species.

One of the easiest ways to start identifying oaks to species is to split them into two groups. The White Oaks have rounded lobes on their leaf margins. I'll cover six species that belong to this group.

The Red Oaks have bristle tipped leaves. They look like little hypodermic needles at the end of each lobe. I'll mention five of these species as well.

Above is the typical shape of the Red Oak batch. This one is Black Oak Quecus velutina. The problem is this shape is also similar to the Red, Scarlet, and Pin Oaks, so you have to dig a little farther than just leaf shape.

The key feature on Black Oak is the fuzzy look and feel of the leaf petiole, buds, and new growth twig.

Look closely at the leaf underside. The main veins and most of the leaf will have a velvety feel, hence the latin name velutina.

The leaves of species in the Red Oak group are notorious for showing variation in shape, and Black Oak is no exception. Leaves found on the lower portions of the tree are fatter and have shallower lobes and sinuses. Even when looking like this, the hairy feel is still obvious. If we stay away from strickly leaf shape, is there anything else to use? How about "da bud".

The buds are covered in hairs from top to bottom. After the leaves die, many will lose the hairy texture, but the buds will remain the same. These are buds from the top of the tree, and are always hairier than the lower buds.

Here are buds from a lower branch. You can see some orange scales popping through, which causes confusion with Scarlet Oak which we'll see in a minute. Examine it up close, especially with a hand lens, and you'll see every scale still covered in hair. Black Oak buds are long pointed and angled like a pyramid.

If the tree is too tall to examine leaves or buds, search the ground for acorns. The caps are bowl shaped like others, but differ in having the rim or edges frayed. In other words each scale stands erect and points upward, like wind blown roof shingles.

Last but not least is the bark. Black Oak has a darker bark than many of the other oaks it grows with. In the upper portions it is striped, and resembles Red and Scarlet, but further down the stripes disappear and it forms a blocky appearance. Many say it has a dirty texture to it due to the lichens and mosses growing on it. This is true, but lichens can grow on any oak, so I don't need to touch it, just look at it and compare it to others. Black Oaks grow in any habitat, but are more common in upland dry soils.

To many, especially those from northern Ohio, this may resemble a Pin Oak. That's why leaf shape in unreliable. This is Scarlet Oak, Quercus coccinea. Both species have deep sinuses like this, appearing as if caterpillars ate away most of the surface area. In our part of the state, Scarlet is only found on upper slopes and ridge tops. Pin Oak is a bottomland species. It is often written that Scarlet Oak leaves show bits of hair gathered at the intersection of leaf veins on the lower surface. Yes they are there, but other oaks show this as well, so I personally never use that trait.

Scarlet does have a similar growth form to Pin, keeping a lot of dead lower branches. Pin Oak forms more of an umbrella with its lower limbs, where Scarlet just looks scrubby. In areas without hills, look for it in dry soils.

The similarity ends when you look at the buds. Scarlet has hairy scales on the top of the bud, and hairless scales on the bottom half. The red and white bud gives it the appearance of snow capped mountains.  Pin Oak buds are brown and hairless.

The acorn cap is bowl shaped like that of Black, but the scales are not erect. They lay flat, appressed against one another.

Many Scarlet Oak acorns will show concentric rings, or a bullseye on the top portion. This is another clue to identification, but not all Scarlets will have these rings.

Here is the Pin Oak, Quercus palustris, showing variation in leaf shape.  Pin Oak is a tree of bottomlands and wet areas. It is not common in unglaciated Ohio, but very abundant in flatlands elsewhere.

Like Scarlet, Pin Oak retains many lower branches, but on this species they are often alive. The lower branches may spread out when the tree is planted in the open. When competing with other trees, those low branches may grow straight down.

This growth form is more easily observed in winter condition.

Pin Oak acorns are some of the smallest of the oaks in Ohio. When maturing they will be covered with white or brown hairs.

After falling, the rain will wash the hair off and expose a two colored look similar to a striped watermelon. You can also rub the hairs off by hand.

The leaf shape of Red Oak Quercus rubra, is the same as Black Oak. Remember though that Black is hairy everywhere. All parts of the Red Oak are hairless and smooth.

Red oak produces a very fat acorn, pumpkin like in shape. The cap does not cover very much of the nut.

The caps are often the size of a quarter. They are quite flat, and resemble a French beret.

Just like the leaves, the buds of Red are completely hairless. If you were bald and spent the summer in the hot sun, you'd be sunburned red like this too.

If there are no leaves, buds, or fruit available, once again the bark is key to identification. The trunk has vertical dark and light gray stripes from top to bottom. The bark looks runny or finger painted.

Red Oak is a clean growing tree, seldom showing much in the way of dead branches. For this reason it is highly valued as a timber species. They grow anywhere, but do best on lower slopes, especially north or east facing hillsides.

Hmm, I'm looking around the ground and I see evidence of acorns present, but nothing that resembles an oak leaf. These can't be it.

Nary a lobe or sinus is anywhere to be found, yet this is an oak. Shingle Oak, Quercus imbricaria. It is our only unlobed oak here in the north. Because of that I don't need to check buds, fruit, or anything else for that matter. Shingle is one of the easiest oaks in Ohio to identify. Of course if you head to the southern states, there are many species with unlobed leaves. So is it a Red or White member?  Look closely at the top of the leaf.

A leaf need not have many bristles on it. This single bristle at the leaf tip puts it in the Red Oak group.

Shingle Oak is a very scraggly growing species. Its branches are often short, thick, and form dense clusters throughout the tree. Shingle also retains a large portion of its leaves through the winter.

All oaks commonly have wasp galls growing on them. It's not unusual for Shingle Oak to be covered with these hard Horned Gouty Galls. Disfiguring maybe, but they really don't interfere with tree growth.

One other thing the previous five species have in common is they all show what I call hard dark bark. That character will change with the next group of species.

Can't think of a better way to start the white oak group than with White Oak Quercus alba itself. The leaves range from shallow to deep lobed, depending where on the tree they're found. There is a slight white look to the undersides. In the central hardwood forest White Oak is the most important species both ecologically and economically.

White Oak buds are smaller and more blunt than members of the Red Oak group. Their twigs are long and narrow, and commonly covered with a white or glaucous coating.

The acorn caps have raised scales or warty bumps. They look covered in goosebumps. These fruit are highly sought after by wildlife including deer, grouse, turkey, and squirrel.

White Oak bark really stands out in a forest. The trunk is covered with small rectangular white plates that easily flake off when rubbed.

In our area, this white oak bark is nearly identical to Swamp White, Chinquapin, and Post Oak. With the exception of Shingle Oak, it is often necessary to use multiple characters in identifying oaks. Buds, leaf, bark, and fruit all play a roll in separating them out. Half of the oaks covered in this post are also limited to specific habitats.

Here is an example. You are walking along and notice a tree with white flaky bark. The leaves look different than White Oak, and there are many scraggly lower branches, both dead and alive. Because you are in a wet bottomland, this is likely something different.

This is Swamp White Oak, Quercus bicolor. The leaves have shallow lobes like several other species, but notice the lobes are all concentrated near the top. There are very few to no lobes at the leaf bottom.

The leaves have a very thick texture to them. The undersides are white and covered with soft velvety hairs.

On large trees the white flaking begins to show long fissures. I never use this, as I don't find it distinct. Don't look at the bottom of the tree, but a bit further up for a hint.

Like Pin Oak, Swamp White branches all tend to droop or grow downward. The silhouette of this tree is helpful in identification. Swamp White is not frequent in our hill country, but more widespread through the rest of Ohio.

Another key feature are the acorns, in particular the stems. They are very long compared to other oaks, and have the look of a pipe.

Post Oak, Quercus stellata, is a species of the south central United States. Its range in Ohio is restricted to the southern half of the state. The leaf is distinct in having its primary lobes widest at the shoulder area. It looks like a cross or ghost. In our area, Post Oak is found strictly on dry ridge tops.

Even if you can't reach the branches, just look up into the crown. That leaf shape will be apparent.

Since we are talking ghost shaped leaves, this is Quercus stellata variety casperi. It is a rare form known as the 'friendly' ghost shape. Wave hi.

It has small acorns, and the caps are covered with raised arrow-head shaped scales.

Post Oak often shows dark and light patches in the bark. Although White Oak can also have a patchwork appearance at times, combining the bark with leaves, fruit, and habitat, insures you have a Post Oak.

Speaking of high slopes and ridge tops, here is another species to look for in those sites. This is Chestnut Oak. The leaves have evenly shallow lobes from top to bottom. In Ohio it is found throughout the unglaciated portions of the state. It was originally known as Quercus montana, then changed to Q. prinus, and has now gone back to montana.

Contrary to most of the white oaks, Chestnut Oak has long, sharply pointed buds. Both the buds and twigs may be a bright orange in color.

The fruit is once again helpful in identification. The caps are shaped like a wine goblet. The nut is elongate and football shaped. I tell students to think of football and Joe Montana to remember the latin name. When these fruits hit the ground in the fall, they immediately start to germinate.

Perhaps the easiest way to identify this tree is by the trunk. Again, it breaks the rule of having white flaky bark. It is deeply furrowed, gray, and very hard. It reminds me of cement. Another common name for this tree is Rock Chestnut Oak.

Here is a species that has acorns and bark similar to White Oak, but leaves similar to Chestnut Oak. This is Chinquapin Oak, Quercus muehlenbergii. In our area it's usually found on lower slopes, and is an indicator of alkaline soils.

Chinquapin Oak leaves are similar to Chestnut Oak, but the lobes are not as rounded. They come to a much sharper point, ending in what I call a little nub. They are serrate, but often incorrectly keyed out as having bristle tips.

The bark is virtually identical to White Oak. The rule for identification: If it has bark like a white, and leaves like a Chestnut, it's Chinquapin.

Here are a couple of pressed specimens of perhaps the strangest and craziest shaped leaves of all the oaks.

These highly variable leaf shapes can only belong to Bur Oak, Quercus macrocarpa. Bur Oak is absent in the Athens County area, but otherwise found throughout Ohio. It grows best when there is little competition, so it is common on field edges, along river floodplains, and in prairie margins.

The bark is similar to Swamp White, but the acorns make it unmistakable. Look for little 'burs' growing on the edge of the cap.

Upon maturity, those burs will have grown into what feel like stiff hairs. Because of this it is often called Mossy-cup Oak. The name macrocarpa refers to the fact that these produce the largest of all acorns. They commonly reach golf ball size, and I've seen a few start to approach a tennis ball in circumference.