How do you come by that figure for the lifespan of urban trees? I'm thinking my own pale little anecdotal experience doesn't jibe with that. Is that a difference between Western and Eastern cities, or am I wrong about the trees in SF, Oakland, and San Jose? -- I mean I could have an error of observation based on missing all the little baby trees that don't make it and are replaced regularly. But that's not what my memory provides me with.