Human impact on the Kiso-hinoki cypress woodland in Japan: a history of exploitation and regeneration

The Kiso-hinoki (Kiso-Japanese cypress, Chamaecyparis obtusa) woodland underwent severe deforestation in the early 17th century, then regenerated through conservation during the Edo period. Now, a suitable management strategy is sought in order to maintain its ecological function in the forest. To understand the vegetation changes and human impact, sediment cores were recovered from Lake Tadachi in the Kiso-hinoki cypress woodland in the central uphill region of Honshu island. In addition, stratigraphic pollen analysis on two cores (Nos. 6 and 10) and phytolith analysis on three strata of one core (No. 6) was conducted. The age-depth models were constructed based on ¹⁴C dating, greyscale analysis on the sediments, and the increasing level of Cryptomeria pollen (about a.d. 1960) from the pollen profiles. In all periods, the dominant pollen taxa were Cupressaceae and Quercus subgen. Lepidobalanus type. Our analysis indicates that after the commencement of Shikinen-sengu, which is the rebuilding of the Ise Grand Shrine every 20 years, Cupressaceae pollen decreased and the woodland was gradually replaced by Quercus subgen. Lepidobalanus. The percentages of Cupressaceae pollen decreased dramatically and the expansion of secondary woodlands was accompanied by an increase of Quercus subgen. Lepidobalanus in the early 17th century cal. a.d. However, depletion of the woodland was determined from a decrease in concentration of Quercus pollen. The conservation activity during the Edo period and after the Meiji Restoration brought about woodland recovery. However, based on our pollen and phytolith analysis, significant changes to the woodland habitats can be detected. These were probably due to human impacts, most notably in the years after World War II. Four major turning points as the result of human influence were identified: the 10th century, the late 16th century, the Meiji restoration (a.d. 1863), and the end of World War II. The original cypress woodland mixed with deciduous broad-leaved elements has been greatly reduced, preventing future cypress woodland regeneration after World War II.