In 2002, a surprising study reported that lianas, or vines, are much more common in the Amazon rain forest than they were decades ago. Researchers have since confirmed this and found that lianas throughout the Americas are indeed growing more rapidly. (In some places, they outpace trees by 60 percent.) Scientists suspect that there's no single cause of this strange trend. Instead, many influences are likely at work, including drought, deforestation, and rising carbon dioxide.