Beijing’s Forbidden City, a UNESCO World Heritage Site since 1987, is one of the world’s largest and best‑preserved ancient wooden structures. More than three times the size of the Louvre Palace in France, the complex is now the focus of Chinese historians and scientists who are using tree‑ring research — and, for the first time, oxygen isotope dendrochronology — to pinpoint the origins of timber and its species, deepening understanding to preserve timbers for centuries to come.
Now, in a new study published in npj Heritage Science — Dating and provenance tracing of historical timbers in the Forbidden City using oxygen isotope dendrochronology — historians at the Palace Museum in Beijing worked with researchers from the State Key Laboratory of Lithospheric and Environmental Coevolution at the Chinese Academy of Sciences to apply this cutting‑edge method to roof beams from the Dagaoxuan Hall complex.
The Forbidden City has stood for more than 600 years as the seat of Chinese imperial power, but its construction and renovation history has often been difficult to determine with precision. Archival records are incomplete, and traditional methods such as stylistic analysis or ring‑width dendrochronology have limitations. As the researchers note, “we lack scientific and precise methodologies to determine the construction and renovation history of this complex.”
By measuring oxygen isotope ratios in tree rings and cross‑matching them with a master chronology from northeast China, the team established an age range for the roof timbers: “Successful matching with an isotopic chronology from northeast China gave an age range from 1749 to 1892, which corresponds precisely with renovation records from documentary.”
The analysis also confirmed that the timbers likely originated from northeast China, providing evidence of a shift in sourcing practices between dynasties. Combined with historical records, the findings show that timber use and provenance in the Forbidden City changed from the Ming to the Qing period. This discovery deepens understanding of how imperial builders managed resources across centuries.
Traditional dendrochronology, based on tree‑ring widths, has been used for decades to date archaeological sites and historic buildings. But irregular growth patterns and missing chronologies often limit its accuracy. Oxygen isotope ratios, by contrast, record stronger climate signals, show less variability between trees, and require smaller samples — making them particularly well suited for fragile archaeological wood. “This is the first reported application of oxygen isotope dendrochronology to the provenance tracing of historical timbers,” the team noted, adding that the technique “confirms the significant potential of this method for tracing the origin of archaeological woods.”
For more information: Zhao, Q., Xu, C., Zhang, Q. et al. Dating and provenance tracing of historical timbers in the Forbidden City using oxygen isotope dendrochronology. npj Herit. Sci. 13, 602 (2025). https://doi.org/10.1038/s40494-025-02172-1
