Harvard Forest scientists study tree rings to track extreme climate events —which are growing more common — over centuries. Four teams of researchers, led by Harvard Forest ecologists, searched for a patch of ancient trees deep in the woods of western Pennsylvania this summer as part of a project to study how climate changes affected trees over the centuries. The project goal is to find and core the oldest trees in the Northeast. Studying the color and size of their rings offers scientists a glimpse into the past, allowing them to see how trees and forests responded to extreme climate events, like droughts or late-spring frosts in the past. …They presented evidence that droughts and harsh spring frosts from 250 years ago affected different forests across hundreds of miles in the Southeast. The disturbances abruptly killed some trees but accelerated the growth of others.