HISTORY WRITTEN IN WOOD

Mute only in words, trees speak volumes to people like David Orwig, a senior ecologist at the Harvard Forest and master of reading landscape history in the rings of trees.

Trees are living timelines. Droughts, wet spells, fires, insect outbreaks, hurricanes, ice storms: they are all written in wood. Rings of annual tree growth, showing light in spring, and dark in summer, record the years of a tree’s life. Suppressed rings mean something stalled the tree’s growth – an event, a neighbor, some changed condition in its environment. Then a big spurt of growth – called a release – narrates the tree bursting free to grow robustly. Rain fell, a big tree nearby crashed over. Something somehow set it loose.

Put together with other records, tree rings, read correctly can be powerful and reliable narrators of history, with an error bar of zero. Here at the Harvard Forest, researchers often combine the extensive land use records in the Harvard Forest Archives with tree ring interpretation to see amazingly fine detail of landscape history.

While here at the forest as a Bullard Fellow I am writing a book about the life of single 100-year old red oak. I’m using all kinds of records and documents in my research, in addition to observations of the tree and the forest to tell its story. I’ve also dug into the Harvard Forest Archives – and watched Orwig core the tree last June to confirm its age. I keep its cores right here on my desk all the time, a touchstone to the tree’s inner life over the years.

This morning, Orwig had some surprising news: he had stumbled across a bit of the oak’s history in the archives in some research of his own. He was reading stand records from another area of the forest, and came across notes about a big gypsy moth attack in 1944. The hand-written field notes in the archives tell a richly textured story of the life of the forest and people who have worked with it since the forest was founded in 1907. Thinning, harvesting, surveying, planting, mapping, records of big storms, fire, and other disturbances – foresters and researchers over the years seem to have recorded just about everything.

The records have been carefully indexed and curated, and many are even digitally scanned for anyone’s use, for free, online. As Orwig read about that gypsy moth attack, something clicked — a memory of the core he pulled from the oak last summer.

“Do you still have that core?” Orwig asked, stopping by at Shaler Hall this morning. We looked at the core together under the microscope in his office, and sure enough, the core bore out his hunch. A strong grower in nearly every year of its history, the oak’s fat, evenly-spaced growth rings march through time. But then there it was, written in wood: a squeeze in the summer growth of the oak in 1945. The gypsy moth attack of 1944.

The insects typically build up over several years, doing cumulative damage to the robustness of trees, and can even kill them. In this case the oak was suppressed just one year, then bounded back.

How exciting to see people and trees each recording history in their own languages, for us to discover all these years later.