Whose trees are at risk?

NATIONWIDE, OAK wilt has been found in 22 states, but only Texas has an epidemic. The reason for the Lone Star State's plight is a semi-monoculture of live oaks. Nearly pure stands are characteristic of Austin and the surrounding woodlands of central Texas.

The ranchers back in the 1800s favored live oaks and cleared off everything else, according to Jim Rooni and Jay Culver, the two urban foresters assigned to Austin's oak-wilt project.

Austin's extensive tree canopy belies the stereotype of a parched and barren Texas. But nearly a third of the city's canopy is live oaks and members of the highly susceptible red-oak family. Rooni and Culver has identified 115 centers of infestation in Austin, each with anywhere from one to hundreds of afflicted trees.

"It virtually looks like a bomb has gone off in some areas of the city," says Rooni.

Although the disease has apparently been present since 1934, it wasn't until 1977 that it was officially diagnosed, with the help of experimental plots at the LBJ ranch. Austin hired its first city forester, John Giedraitis, in 1985, and two years later hundreds of volunteers organized a two-day Live Oak Festival to raise funds for trenching. A year after that, Texas Congressman J.J. "Jake" Pickle persuaded the U.S. Forest Service to begin providing federal funds, which are channeled through the Texas Forest Service.

Ed Barron, head of the agency's Forest Resource Department, says more than $6 million has been spent to date battling the disease statewide, and 177 miles of barrier trenches have been installed. The program has saved as estimated $60 million worth of trees.

In an effort to assess the financial impact of oak wilt, researchers at Texas A&M conducted a study in 1989 and determined that trees represent between 13 and 19 percent of the property value of the average Austin home.

The trees in the Castlewood neighborhood where Bill Peters lives tend to be large, so the higher end of the scale is probably applicable. Castlewood homes average more than $100,000 in value, meaning that trees represent a minimum of $19,000 of each home's property value. Since a third of the tree canopy is live oaks and red oaks, the loss of Bill Peters' trees theoretically could have lowered his property value more than $6,000 Citywide, the loss is estimated at between $800 million and $1.6 billion.

"As opposed to insects that go through cycles and die, oak wilt just doesn't go away," Ed bArron points out. "Austin probably hasn't hit its peak yet. It's a difficult disease to combat in urban areas where you have to organize so many property owners.

"The disease moves so fast that your trees are probably already gone while you're trying to raise money to protect your neighbor's trees," Barron adds. "Sometimes I wonder whether we're gaining on this thing, but we've certainly helped a lot of people save a lot of trees. And we're buying time to develop a healthier urban forest."

There are several lessons to be learned from Austin's oak-wilt tragedy and from the devastation wrought by other plagues such as Dutch elm disease as well as environmental disasters--fire, flood, freeze, and drought. One is the importance of diversifying tree species in the urban forest, thus preventing widespread canopy loss should disease strike. Another is the important role communities play in protecting and maintaining their urban forest; citizens' ability to act to restore their trees will determine how well a community recovers from this type of disaster. And finally, citizens should realize the ecological effects that major tree devastation can have on their community as a whole, contributing to shade and energy loss, stormwater-control problems, erosion, and water quality.

For cities that already have a broad diversity of species, the recommended planting diversity for a genus such as oaks is a maximum of 10 percent of the urban forest; no more than 5 percent of the total should be a single species such as live oaks. Stick to the 10 and 5 percent standard, and your city will have a fighting chance of avoiding tree epidemics.