Review: Vegetation history of Cryptomeria japonica in Japan since the last interglacial period

Abstract

The natural distribution of Japanese cedar (Cryptomeria japonica) has been disturbed by human activities, owing mainly to its value as timber; thus, its position in the vegetation zone of Japan is not clear. Therefore, it is important to determine the history of C. japonica forests before human influence. We reviewed the transitions in distribution and abundance of C. japonica in the Japanese Archipelago since the last interglacial period by using published pollen data. During the last interglacial, temperate deciduous broadleaf forests developed on northeastern Honshu Island, whereas on southwestern Honshu Island C. japonica populations increased, accompanied by warm-temperate evergreen broadleaf trees. During the first half of the last glacial period, C. japonica forests developed throughout the Japanese Archipelago except on Hokkaido. Thereafter, 60,000-30,000 years ago, C. japonica covered the area around Lake Biwa and the Izu Peninsula. During the Last Glacial Maximum, C. japonica was most abundant on the Izu Peninsula, and small refugial populations were located along the coast of the Sea of Japan from southwestern to northeastern Honshu, and along the Pacific coast of Shikoku Island. During the Middle Holocene, C. japonica populations increased rapidly in southwestern Honshu. Two thousand years ago, before the intensification of human activities, C. japonica was widespread in warm-to cool-temperate zones on the Sea of Japan side of Honshu, the Izu Peninsula, the Pacific coast of Shikoku Island, and Yakushima Island. This evidence indicates that C. japonica is one of the major tree species in the Japanese vegetation zone.

Review: Genetic structure and local adaptation in natural forests of Cryptomeria japonica

“…Areas shaded in diagonal lines are respectively refugia (Izu Peninsula, Wakasa Bay, Oki Is., and Yakushima Is.) and probable refugia at that time (Takahara, 1998; Tsukada, 1986). The investigated 14 populations were showed three letters, which are same populations in Figures 3 and 5.…”

“…Cryptomeria japonica is thought to have been distributed in refugia during glacial periods, especially during the last glacial maximum (LGM), mainly in refugia such as those around Izu Peninsula, Wakasa Bay to Oki Island, on the southern Kii Peninsula and Shikoku Island, and Yakushima Island in southwestern Japan (Tsukada, 1986; Figure 1). Isolated small refugia are believed to have been distributed in Tohoku district of northern Japan (Takahara, 1998). The refugia population migrated to the northeastern part of Japan in the postglacial period, and then the current natural forest was established.…”

Preface: Functional biogeography in Japanese cedar

“…Its amount of academic information is comparable to that of the European beech ( Fagus sylvatica ), the Scots pine ( Pinus sylvestris ), and the Norway spruce ( Picea abies ) in Europe (e.g., Benavides et al, 2021; Schulze, 2000; Vila‐Cabrera et al, 2015). In the case of the Japanese cedar, the genetic diversity remained after the presence of several refugia even in the Last Glacial Maximum (LGM; Takahara et al, 2023; Tsumura, 2022), and therefore, it is expected that the geographic, genetic, and functional variations are also large. Based on these characteristics, the Japanese cedar will provide a good material for investigating the response of each local forest ecosystem under climate change, based on the geographic functional differentiation and its cascading effects.…”

“…Genetic analysis suggests that the LGM refugia existed at least near the Izu Peninsula, southern Kii Peninsula, southern Shikoku, Wakasa Bay, and Yaku Island (Tsumura, 2023). Since pollen fossils during the LGM have been found at four of these sites from regions other than the southern Kii Peninsula, as well as from Sado Island, Oki Island, and western Chugoku (Takahara et al, 2023), it is considered that the LGM expanded its distribution from at least these eight regions to form its present distribution area with global warming (Figure 1). Therefore, it is presumed that the variation in functional traits of the Japanese cedar also reflects the characteristics of these refugial populations to some extent.…”