Pando, in central Utah, looks like a grove of about 47,000 quaking aspens spread over roughly 106 acres. It is one tree. Every trunk is a shoot from a single root system, all genetically the same, and when a trunk dies, usually somewhere past its first century, the roots send up another. Nobody can say how old the roots are, because tree rings only date the trunks; estimates run to thousands of years. What’s going wrong there now is not age. Deer and elk eat the new shoots before they get tall, so the old trunks keep dying and nothing comes up behind them. Where researchers fenced a plot to keep the animals out, young aspens came back thick within a few years. A thing can be ancient, enormous and alive, and still be only as safe as its newest shoot.