The properties of cold environment for Thujopsis dolabrata var. hondai and Criptomeria japonica in the northeastern Japan

Abstract

Cryptomeria japonica and Thujopsis dolabrata var. hondai have similar life-form and make the cooltemperate coniferous forest in Japan. It was thought that these two species had different process of spread of distribution in the postglacial time. During the postglacial period in northeast Japan, C. japonica migrated from south to northeast and Th. dolabrata var. hondai developed from ice age refugia scattered there.The purpose of the present paper is to explain the difference of behavior between the two, based on the relation between the present distribution of habitat and climatic condition. The results are follows.(1) C. Japonica is restricted in Honshu under the climate of Japan Sea type and Th. dolabrata var. hondai reaches to southern Hokkaido under climate of Japan Sea and Pacific-Japan Sea transitional type; annual water surplus by Thornthwaite's method is over 800mm for C. Japonica and under 1, 400mm for Th. dolabrata var. hondai; minimum and maximum value of total winter (December, January and February) precipitation is 300mm and 900mm for C. japonica and 150mm and 600mm for Th. dolabrata var. hondai, respectively.(2) The lower limit of thermal condition for Th. dolabrata var. hondai is closely related with the condition of hydro-climate. It can reach to coldest condition about 25°C Month of warmth index under 700mm of the annual water surplus or 200mm-300mm of total winter precipitation. Th. dolabrata var. hondai grows in the mountain and subalpine zone with Tuga diversifolia, Abies mariesii and others and even in alpine zone where it is stunted conspicuously and flourishes in the shrub and herb layers. For C. Japonica, however, the properties as seen for Th. dolabrata var. hondai can not be recognized.(3) If the lowering mean annual temperature was 7°C at the maximum of the last glaciation, the altitude of 25°C Month warmth index is estimated about 500m above the sea level in Tohoku and about 200m a. s. l. in the Oshima peninsula, southern Hokkaido. Considering the present behavior of Th. dolabrata var. hondai and C. japonica, it is able to interpret that the Th. dolabrata var. hondai contracted into scattered refuges in Tohoku and southern Hokkaido under the condition of less winter precipitation, although C. japonica had not been able to grow in southern Hokkaido during the full glacial interval.