In the megacities that are home to nearly 10 percent of the world's 7.5 billion people, trees provide each city with more than $500 million each year in services that make urban environments cleaner, more affordable and more pleasant places to live.In a recent study published in the online journal Ecological Modelling, an international team of researchers reported that in the 10 megacities they studied, tree-based ecosystem benefits had a median annual value of $505 million, which is equivalent to $1.2 million per square kilometer of trees. From another perspective, the value was $35 per capita for the average megacity resident.