BOULDER - Ethan Welty is thinking ahead to harvest time as he cycles through tidy streets pointing out apple, plum and mulberry trees on public and private land.

"We're coming up on the best apple trees in Boulder," said Welty, a geographer and Ph.D. student specializing in glaciers in the University of Colorado's Environmental Studies program. He was approaching a front-yard grove of trees.

Last summer and fall, Welty said, he never went to a supermarket for fruit. He had two apple trees in his own yard, but began looking for more produce when he bought a cider press. Once he started paying attention, he was astonished at the bounty, and determined it should be shared. Now, it can be, thanks to a website Welty started with a fellow CU student with shared interests in computers and urban foraging.

And the sharing goes well beyond Boulder.

Want to find walnuts free for the picking in Iowa City? Locate loquats in New Orleans? Discover where a mulberry tree grows in Brooklyn? Check out, the site Welty and Caleb Phillips launched in March. They have gathered information mapped by amateur enthusiasts across the country and delved into inventories many cities and towns keep of trees on public spaces. And has gone international, with information coming from Australia, Britain, India, Israel and elsewhere.

Users first click on a hot spot on the site's large-scale map. Then, with a series of clicks to more and more detailed maps, home in on, say, a myrtle in Tallahassee, Fla. A spotter has added a note about its guava-like fruit - "a bunch, and super tasty." Links from there lead to more information from the Department of Agriculture or Wikipedia about a particular plant. Welty and Phillips welcome additions and updates.