Hinoki Cypress Bark Stripping and Thickness Grading: Harvesting Methods in Hiwadabuki

In the steep, mist-shrouded mountain valleys of Kyoto, Nara, and Gifu prefectures, the harvesting of Hinoki cypress bark (Chamaecyparis obtusa) represents one of the most sophisticated examples of ancient forestry stewardship in human history. To supply the national conservation demands of Japan's National Treasures and Important Cultural Properties, forestry guilds maintain strict ecological protocols developed over a thousand years.

A Hinoki tree is considered eligible for bark harvesting only after it has reached a minimum age of eighty to one hundred years, with a trunk diameter exceeding forty centimeters. At this mature stage, the tree has developed a thick, multi-layered protective outer bark (rhytidome). The harvesting process—known as nagara-muki—is non-destructive. Unlike commercial timber logging, where trees are clear-cut, nagara-muki harvests the living tree in situ, allowing the forest to remain standing and healthy while yielding precious architectural materials across centuries.

Executing nagara-muki requires supreme physical courage, athletic dexterity, and profound botanical intuition. Operating in teams of two, the master harvester (motokaki) ascends the ancient cypress trunk using specialized climbing spikes (ashiba) and a heavy hemp safety rope. Working at dizzying heights between fifteen and twenty-five meters above the rocky mountain slope, the harvester begins peeling from the upper canopy downward.

The artisan makes a shallow horizontal incision through the outer bark using a curved knife. Crucially, the blade is controlled to penetrate strictly through the dead, fibrous bark without ever contacting the smooth, moist green cambium layer beneath. Inserting the beveled edge of a wooden or bone peeling spud (kaki-bera), the harvester leverages the bark away from the trunk. The bark separates in long, continuous ribbons measuring one to two meters in length and fifteen to twenty centimeters in width. As the ribbon peels free, it falls to the forest floor, where apprentices gather, bundle, and catalog the harvest.

Freshly harvested Hinoki bark contains significant moisture and is encrusted with forest debris, lichen, and moss. If bundled and installed green, the trapped moisture would foster internal fungal decay and cause uneven shrinkage, loosening the bamboo fasteners. Therefore, the raw bark ribbons are transported to covered drying sheds where they are stacked upright in open wooden cribs to air-cure for two to three months.

Once dried to an equilibrium moisture content of 12 to 15%, the bark undergoes meticulous surface dressing. Working at a low wooden bench, the craftsman uses a hiwada-kaki—a specialized two-handled drawknife with a curved, razor-sharp steel blade. Drawing the knife toward the body, the artisan scrapes away the weathered grey exterior layer, stripping off brittle lichen and dirt until the rich, glowing, reddish-brown fibrous body of the cypress bark is exposed. The ends are then trimmed square with a heavy cleaver (nata) to a standardized architectural length of 750 mm (approximately 2.5 traditional shaku).

The final workshop phase is the rigorous sorting and grading of the dressed bark strips. Because a natural tree produces bark of varying density and thickness depending on trunk elevation and sun exposure, master roofers divide the material into three distinct functional grades.

The thickest, densest strips—measuring 3.5 to 5.0 mm in thickness—are designated as Noki-kawa (eave bark). Possessing high stiffness and maximum resin content, Noki-kawa is reserved exclusively for the heavily packed, exposed eave edges (nokisaki), where it must resist driving rain and heavy winter snow loads. Medium-thickness strips (2.0 to 3.5 mm) are classified as Hira-kawa (field bark), utilized for general shingling across the expansive primary roof planes. Finally, the thinnest, most pliable ribbons (1.0 to 2.0 mm) are graded as Mune-kawa (ridge bark). These ultra-flexible strips are used to wrap the tight convex curvatures of the monumental central ridge cap and the delicate sweeping margins of the hafu bargeboards, ensuring that every zone of the roof receives bark calibrated to its precise structural demands.