It's tough at the top.

• Position: Science - Trees - Brief Article

In Humboldt Redwoods State Park in California stands a 369-foot-high tree--as high as a 30-story building. It's the tallest organism on Earth, and still growing. So how tall can a tree get? In a recent study, scientists predicted that no tree can grow higher than 400 to 427 feet. First they hauled themselves to the tops of the world's tallest trees. "It's quite an amazing feeling," says George Koch, an ecologist at Northern Arizona University. Koch and the other researchers found that leaves higher up suffered progressively from a lack of water (which is...