Here's the scoop.

I guess "the tree is destroying my foundation" is better than "oops."

I've read that the problem is that concrete cuts off a tree's access to water and other necessities of life, meaning its roots reach higher and higher. This causes cracked sidewalks and trees that aren't rooted deeply enough to withstand heavy rainfall. (But I'm not an expert, so perhaps someone who is could verify this.)

There are nine walnut trees left. What happens next?

Here's one option: RubberSidewalks made from recycled tires. (Dear God, please don't let this be a segue into another prostitute conversation.) They're designed with spaces to prevent suffocating the tree. Plus, you can cut out the bottom to fit existing tree roots.

From their web site: "According to the U.S. Dept. of Forestry, it takes approx. 70 new trees to equal the environmental benefits of just one mature tree. The avg. replacement cost per tree is $3,794.00 (detailed in the City of Boise, Idaho, Municipal Forest Resource Analysis by Center for Urban Forest Research, USDA Forest Service, Pacific Southwest Research Station)."

The good news: The city is testing them at EnviroHouse, the green building model home at the dump.

The bad news: They're really expensive.

I'm headed home to go appreciate some trees. Post some other ideas here, fellow tree-climbers.