"Dearest Golden Elm", wrote one correspondent earlier this month, "I finally found you! I see you every day on my way to uni, but I had no idea of what kind of tree you are. You are the most beautiful tree in the city and I love you."

About 3,000 emails have been sent to individual trees in the last two years. This didn't start out as an exercise in sentiment, but a hard-headed attempt by Melbourne city council to manage an urban forest in decline - as a result of drought, by 2009 40% of the 77,000 trees in Australia's "garden city" were struggling or dying.

Map of London trees