For three years I lived in a tiny second-floor studio in the heart of San Francisco’s infamous Tenderloin district. Level with my window was the top of a beautiful medium-sized elm tree. Beyond the tree stretched a rank alley, which bumped up against the back of a fire station. I was surrounded day and night by sirens, drunken shouts and the thunder of the city.

But I found that if I lay on the floor in just the right spot, all I could see were the branches and leaves of the tree and the blue sky beyond. Most of the time this was the closest I could get to nature. Thinking back, I realize the tree was key to keeping up my spirits during those hard times.

Tree-lined streets: Equal to a $10K raise?

We all depend on trees in a more basic way. As Judith Horstman wrote in the magazine Bioenergy Connection, trees "are our master recyclers, guardians of the air, water and soil -- the very lungs of the planet." Besides supplying oxygen and cooling shade, trees and forests also provide vast amounts of carbon and energy. But trees offer other more intangible benefits, as any nature lover instinctively knows.

Luke James is a freelance writer and musician who writes about music, soccer, kids, pets and life with his family in northern California.