Essays

Wild On The Prairie: Habitats

The Oak Tree and the Urban Forest
February 27, 2000

West Texans have planted thousands of oak trees. Most are live oaks or red oaks, with a sprinkled smattering of burr oaks. Oak trees are beautiful, and despite a reputation for being slow-growing, have performed well as ornamental trees. Oak-wilt fungus has killed a few of the oaks (especially in neighborhoods where homeowners with automated irrigation set for ten minutes a day puts down 100 inches of moisture per year).

Oak trees are familiar to those who travel often to Central Texas. If a person has spent any time in Austin most likely he or she has a memory of a good time spent under an oak tree. Many people have watched or fed a tree squirrel while picnicking at a Hill Country roadside park. Oak trees are living things symbolizing much more than just their own “treeness.”

Everyone knows oak trees live a very long time. Many people know the story of the Treaty Oak in Austin, or of other famous oaks, especially in the original thirteen colonies. Oaks symbolize steadfastness, wisdom (because of their ability to reach great age), and shelter. Think of the Celtic tree of knowledge – it, too, is an oak. Oak wood burns hot, without smoke, so oaks also symbolize truth and purity to some people. When a person uses a living object as a symbol, it becomes something that can be related to with emotion. People love oaks.

Since people love oaks, they plant them in their home landscapes. Unbeknownst to the homeowner, however, many other organisms benefit. In the mid-1960s, oaks began to be regularly planted in Midland. Within five years, local birdwatchers began noticing Blue Jays where none had ever been before. Blue Jays were common in Big Spring, but not in Midland or Odessa. During the 1970s, Blue Jays visited every winter. At first, the sighting of a Blue Jay was special, enough so that birdwatchers called each other to go see the unusual visitor. By the mid-1980s, people started to report fledglings, and a little later, baby Blue Jays in nests. Blue Jays are now a permanent part of the natural world of Midland.

In the 1990s, the birdwatchers began to find Chickadees. A few were Mountain Chickadees from the Davis Mountains or Guadalupe Mountains, but most have been Carolina Chickadees. Carolina Chickadees breed east of a line running from San Angelo to Coleman to Abilene and on northeast to the Wichita Mountains of Oklahoma. In the late 1990’s, fledgling Carolina Chickadees were found. Will Carolina Chickadees also become a permanent part of Midland’s landscape?

Why did non-migratory birds such as the Blue Jay and Carolina Chickadee come to Midland? Why would they leave their “preferred” ecological community? Did an ecological catastrophe occur in their native range? When asked, 9 out of 10 people polled agree with that assumption.

Most information about the natural world in the “temporal media” (i.e. television, newspaper, magazines) is of a negative nature. That is not the publisher’s fault -- for it is human nature to be more attracted to catastrophe than normality. Humans want to hear that the sky is falling, that doom is nigh, that the end is near. Luckily, amateur and professional scientists have other sources of information to determine why Blue Jays and Carolina Chickadees moved to Midland.

Hundreds, if not thousands, of birdwatchers keep records of the birds they see. By looking at American Birds, Wilson Notes, and other ornithological journals, and by communicating with other birdwatchers statewide, a person can develop alternative hypotheses.

Both Jays and Chickadees will produce two to five eggs per mated pair. Chickadees live three or four years, and Blue Jays an average of six years. (Both can live longer – but the world is full of predators, bad weather, cars and other obstacles to survival.) In each bird’s life span, only one baby needs to make it to reproductive success to perpetuate the species.

Some years, not one baby will make it to adulthood. In other years, all of the babies will. When that happens, the young disperse. Sometimes the young can find new territories only a mile or two from home. Sometimes they must travel for days before the right habitat can be found again. Some researchers think that a small percentage of every animal population is genetically programmed to seek out and find new habitat.

Do Blue Jays and Carolina Chickadees like all species of oaks? If you have ever hiked in the sand dunes near Crane or Monahans or Kermit, you know that shinoaks cover the dunes. Jays and Chickadees do not live in the dunes. Both species of birds prefer oaks at least 25 feet tall. (There is a surprising amount of freestanding water in the dunes, so the limiting factor in dunes for Chickadees and Jays is not a lack of availability of water.)

The only negative mentioned, so far, in this discussion on the introduction of oaks to Midland landscapes has been the oak wilt virus. Several other somewhat unpleasant organisms came along in the rootballs of oaks dug from the wild.

A number of trees in Midland have Briar sprouting at the base of the trunk. Birds like the berries of briar, but humans do not like to get scratched by its thorns. A few oaks also have Poison Ivy crawling up their trunks. Again, birds like the berries, and humans like the color of the fall foliage, but rubbing a leaf or twig results in rashes and watery blisters which are quite icky. Diversity is a major tenet of modern ecological theory, but that is too much diversity for most folks!

But… now that we have mentioned diversity, it is amazing how much diversity has been brought to our local environment by oaks. Many species of birds that winter here spend most of their time in oaks. Brown Creepers, Red-breasted and White-breasted Nuthatches, and Ruby and Golden-Crowned Kinglets all glean the tough leathery leaves for insect eggs and aphids hidden in the cracks of the bark. Woodpeckers of several species visit every year or two, to spend a month near one grouping of oaks in a neighborhood.

If a person looks a bit more closely, then an incredible variety of tiny organisms can be found on oaks. Wasps, midges, mites, and bacteria cause strange growths (known as galls) on oaks. Several species of lichen and fungus live symbiotically on oaks, as well. Carpenter ants came here in oak firewood, and now live within some landscape oaks. We have only touched lightly on the diversity added to the local ecology by oaks. Keep your eyes open – who knows what will be found!