A library of time inside a temple
The main Buddha hall at Naesosa Temple, the Daeungbojeon, is a religious site and its wooden pillars are a priceless scientific archive. Built in 1633 by the monk Cheongmin, the hall was constructed from massive logs of the Zelkova serrata tree, known locally as neutinamu. These pillars, along with ancient living Zelkova trees on the temple grounds, contain a continuous, overlapping record of tree-ring growth that records Korea's climate history.
Dendrochronology is the science of dating past events by studying tree rings. Each year, a tree adds a new layer of growth, with the ring's width depending on environmental conditions. A wide ring indicates a good growing season with ample rain and favorable temperatures, while a narrow ring points to stress, such as drought or a cold spell. Scientists analyze these patterns of wide and narrow rings to build a timeline. By taking core samples from the Daeungbojeon's pillars and from living trees—some over 1,000 years old—researchers can match the overlapping patterns, creating a master chronology that extends back centuries.
Decoding the wooden past
This Zelkova master chronology from Naesosa is a reference tool for Korean history and climate science. The continuous, year-by-year record allows archaeologists to precisely date wooden artifacts found at other sites. If a wooden beam from an old fortress has a ring pattern that matches the Naesosa record from, for example, the years 1350 to 1450, its felling date can be determined with high accuracy.
The data also allows for detailed climate reconstruction. The ring widths from Naesosa's trees correlate strongly with summer precipitation and temperature, giving scientists a proxy for weather conditions long before instrumental records began. This information helps identify historical periods of drought, extended monsoons, and other significant climate events that would have affected agriculture and society. The study of stable oxygen isotopes (δ18O) within the wood's cellulose provides another layer of data, offering further clues about past rainfall patterns and humidity. Tree-ring data from across the Korean peninsula helps researchers understand larger climate dynamics, including the East Asian summer monsoon and patterns like the El Niño–Southern Oscillation.