You can tell how old a tree is by counting its rings, but those rings have a lot more to say. And if you live in California, which is in the midst of a four-year drought, you may want to listen.
Dan Griffin — the subject of “Tree Hunter,” directed by Jamie Schutz — uses trees as history books. He studies their past precipitation patterns and uses that information to forecast future precipitation and advise California water management officials. This film is part of “The Collectors,” a series of short documentaries from FiveThirtyEight and ESPN Films.