Cryptomeria Japonica: Glacial Refugia and Late‐Glacial and Postglacial Migration

Abstract

Cryptomeria japonica had multiple refugia in Japan where relatively moist, cool climates prevailed during the last glacial period. Its expansion began from scattered full—glacial centers of distribution °15 000 yr ago, reaching its maximum abundance from °7000—2000 yr ago. On one migration pathway, along the southwestern Japan Sea coast, the movement was initially from the coastal refugia to the interior mountains, and was then toward the southern limit of modern distribution; however, the arrival of the species was greatly delayed in Kyushu and Tsushima Islands. Here, the initial stock of Cryptomeria plants was probably brought from Honshu by prehistoric man °2500 yr ago. Cryptomeria reached its northern limit by 3000 yr ago through the coastal route along the Sea of Japan. The population which migrated from the Izu Peninsula area along the Pacific coast did not arrive in Sendai until °1500 yr ago. In Shikoku, Cryptomeria stands were probably continuous with those on the Kii Peninsula during the full—glacial period, but have been isolated for about the last 12 000 yr. After its arrival at each site, a population of Cryptomeria behaved in either of two ways: in a less moist area, it increased slowly in abundance, hardly reaching the 20% pollen frequency level at its maximum occurrence, while in a humid area (> 2000 mm annual precipitation) it increased logistically to an asymptote (represented by generally 50% of the fossil pollen spectra).