Until recently, cities haven't had a good handle on their trees. Generally, they've not kept good records of where their trees are, which ones need attention, and what "ecosystem services" (say, in reducing pollution) they provide.
That's changing because of OpenTreeMap, open-source software that's powering more than a dozen urban tree-inventory initiatives. Philadelphia now has PhillyTreeMap (56,884 trees and counting). Tampa has Tampa Tree Map (2,669 trees so far). And San Diego has San Diego Tree Map (340,952 trees). And more projects are on the way.
"One of the big gaps in managing many cities is around trees," says Robert Cheetham, CEO of Azavea, which has developed many of the services. "Cities are responsible for them when something goes wrong and have to clean them up. But often they have poor or little information about trees that make up the urban forest."
Some cities use OpenTreeMap as a back-end management system, others also allow citizens to map trees themselves, filling out the collective database. "There are a lot of people who are passionate about trees, so we thought, 'Would there be a way matching up that public enthusiasm with a civic need to get better information about trees?'" Cheetham says.
More than 1.1 million trees have now been documented in all, including maps outside the U.S. Azavea has also worked with the U.K.'s Open University to develop Treezilla, a "monster map" of British trees (30,384 and counting).
To add a tree, spotters enter a location, measure the size of the specimen and put in a species (among other data). That allows the system to calculate benefits like CO2 storage, water and energy conservation, and reduction in airborne pollution. The numbers are based on i-Tree, a system developed by the U.S. Forest Service (which we wrote about here).
Quantifying the benefit of trees makes arguing for them easier. And, the maps should allow better planning, Cheetham says. Azavea is currently working on a prototype that simulates tree plantings and their impacts, which it plans to add to OpenTreeMap at end of the summer. It will help planners work out where to plant trees for maximum environmental effect, and to understand how rows of trees might perform over their lifetimes.
"A city can say 'if I plant 100 Red Maples along here, and assume a certain mortality and replacement rate, there will ecosystem service value of X at five, 10 and 25 years'," Cheetham explains. "They'll be able play out what will happen."
All being well, in the future we should have a much better understanding of the value trees provide.