Why ancient grasslands, once plowed, don't grow back the same

When a 10,000-year-old prairie is plowed up to plant corn or a savanna is consumed by a strip mall, these once-grassy expanses, if left to regrow, can eventually look vaguely like they did before. But a growing body of research suggests that what comes back isn't the same as what was lost, even decades later. And now scientists are starting to understand why.