"Stature and beauty aside, trees have a positive effect on physical and mental health, they bring financial benefits to the cities where they grow and they are good for urban wildlife," says Alyssa McDonald at the New Statesman. ... The heatwave that hit Europe in 2003 killed 2,000 people in Britain alone, the argument goes, and cities get hotter than rural areas, because buildings retain warmth. But trees have the opposite effect: while shade from their branches cools people under them, evaporation from their leaves cools the air around them."