San Francisco is the test site for a new crowdsourcing project called Urban Forest Map. The idea is to get citizens to help create a complete census of the city's trees. This information will then "help urban foresters and city planners to better manage trees in specific areas, track and combat tree pests and diseases, and plan future tree plantings." Here's a video.
And there are other, external benefits to the tree census: Involving the community in this project reminds people that trees exist, and that they sometimes produce stuff you can eat. This program seems totally awesome.