The reason I posted the 2 articles on the grand effect of planting trees, is that it is specifically related to Jared Diamond's theses about the rise and fall of prosperous societies.

As we are seeing in his book, Guns, Germs and Steel, the reason for the great prosperity - "cargo" in Yali's term - of white people, is the pure luck of people who found themselves in the "Fertile crescent" having at their disposal a habitat rich in nutritious grains. After learning to cultivate it, they were able to live in permanent settlements and this led to specialization of activities, including metalurgy. A side effect of this living arrangement was the evolution of their immunity to germs. These two things in particular gave them a great advantage over peoples who had no such abundant nutritious food supply.

It is not, however, due to luck that societies collapse. The main thesis in his second book, Collapse is that great societies disappear in direct proportion to their misuse and exhausting of their land's natural resources. The 2 true stories on trees are vivid reminders of just how important our ecosystems are.

Professor Kahn