We have a lot of different oak trees in the region, but, for today, let’s focus on one that has some unique and interesting features: the interior live oak (Quercus wislizeni).

These trees can grow in a tall tree formation, reaching heights of between 30 and 70 feet, or they can grow in a low, scrubby shrub formation (between 6 and 20 feet tall), depending on their habitat. But unlike some of their oak cousins, the interior live oaks have relatively thin bark, so they don’t do as well in high-fire areas as, say, the blue oaks (Quercus douglasii).

They can, however, grow in some places where other oaks can’t, including areas where the soil is comprised of igneous rock (rocks made of molten material) or even granite. Part of the reason for that is that the interiors have the ability to dig down deep into the ground to find sources of water other oak trees may miss.

In fact, studies indicate that they have the deepest root structures of all oak trees across the globe. In Placer County, the roots of one tree were traced down through over 24 feet of rock before they touched groundwater. The leaves of interior live oaks are pretty interesting, too. They are generally flat, thick (sclerophyllous) and evergreen. These thick leaves help the trees to retain moisture in the hot summer months.

Another interesting fact: They actually sport two different leaf shapes on the same tree. New leaves resprouting from a root ball or growing on the lower branches of an established tree have a serrated edge and look almost like holly leaves. The more mature leaves further up into the crown of the tree have smooth edges.

It’s believed that the serrated version of the leaves was an adaptation by the tree to try to discourage deer from eating the younger, more tender leaves.

Deer can really decimate young interior live oaks by their foraging, which is why in some reserves and refuges where there’s restoration work going on, you see the younger trees surrounded by chicken wire or some other defensive barrier.

Once established, the interiors can live for about 200 years. Because they have the ability to resprout from the rootstock after a wildfire, it’s believed that many of the trees we see actually have root systems that are much older (by several generations) than the above-ground trees themselves.

Interior live oaks are home to a variety of nesting birds and squirrels and are host trees to several different kinds of butterflies, like the California sister. If you look carefully on the leaves of these oaks, you can also see that they build specialized galls to feed and protect the larvae of several different cynipid wasps.

Some of galls that can be found right now are the tiny two-horned galls, pumpkin galls, and kernel galls (which look like little green jugs with a reddish-brown lid on them). The kernel galls form on the underside of the leaves along the mid-vein.

The interior live oak is a common tree in this area, but it has some incredible adaptations and features that make it unique. And, while both the interior live oak and the coast live oak (Quercus agrifolia) are native to California, the interior live oak is actually endemic to the state, found here and nowhere else on Earth.

— Mary K. Hanson is a certified California naturalist, author and nature photographer, living with terminal cancer. She developed and helps to teach the naturalist program at Tuleyome, a 501(c)(3) nonprofit conservation organization based in Woodland. For more information, see the website at http://tuleyome.org.

Crossposted from the Davis Enterprise

Published online on July 24, 2019 | Printed in the July 24, 2019 edition on page A7