POLLEN SUCCESSION, ABSOLUTE POLLEN FREQUENCY, AND RECURRENCE SURFACES IN CENTRAL JAPAN

A generalized pollen diagram, associated with three simplified pollen diagrams from Tsubogakure (1,500 m), Nakatashiro (1,400 m) and Yashima-ga-hara (1,650 m) bogs in central Japan, represents five pollen zones for the last 12,000 years, i.e., L (before 10,500 B.P., pine-boreal); R I (10,500-9,500 B.P., boreal-oak); R II (9,500-4,500 B.P., temperate); R IlIa (4,500-1,500 B.P., temperate-boreal); and R IIlb (after 1,500 B.P., pine-nonarboreal). Absolute pollen frequency is high in well-humified peat, in gyttja (deposited immediately below the first peat formation), and in peat in the part of the R IIIa cooling stage, and it is low in less-humified peat, since the former sediments have slow and the latter rapid rates of accumulation, respectively. Changes of plant communities should affect the absolute pollen frequency, but changes of sedimentation rates are more critical. After a re-examination of Nakatashiro bog, it is hardly possible to recognize a recurrence surface in the European sense, nor can the accumulation of thin tephra on the bog surface be responsible for a temporary halt in peat growth. Nakatashiro bog (like Tsubogakure bog) is a low-moor bog, and true recurrence surfaces would not be expected in it. In a raised Yashima-ga-hara bog, however, there are seven recurrence surfaces without a volcanic ash band; the well-humified horizons correspond to low values of Sphagnum spores and Cyperaceae pollen, and the less-humified horizons to high values of Sphagnum spores and Cyperaceae pollen. Peaks of these species in the upper core correspond to those Cryptomeria pollen, an indicator of the high precipitation (generally > 1,800 mm/yr). Regularly interrelated fluctuations among these species, absolute pollen frequency, and peat horizons suggest that the precipitation was low in well-humified peat and was high in less-humified peat. THE LATE Pleistocene pollen history in Japan has been a subject of interest among ecologists since the early 1930's. The gross features of the latest part of the late-glacial and postglacial pollen succession are reasonably clear. Japanese postglacial pollen zones R I, R I-II, R II, and R III, based on two pollen diagrams from Ozega-hara, central Honshu, were correlated with von Post's three-phase postglacial sequence (Nakamura, 1952). A similar trend characterized a raised bog, Yashima-ga-hara, in the subalpine zone of central Japan (Hori, 1957). Recent work (Tsukada, 1967a, b) suggests, however, that Nakamura's R I-II is unnecessary and that R III can be divided into two parts, R IIla and R IlIb. Important as it is, the absolute pollen frequency (APF) estimation tends to be disregarded by many workers. It is a valuable, and perhaps essential, approach to the ecologic aspects of 1 Received for publication 6 June 1966. This study was supported in part by the National Science Foundation (GB-2421 and GB-3811) and by the Penrose Fund (3843) of the American Philosophical Society. The author thanks Professor E. S. Deevey for his invaluable advice and support of the work; Dr. P. A. Colinvaux, Dr. M. B. Davis, Dr. C. J. Heusser, and Dr. J. Iversen for their helpful criticisms; and Dr. M. Stuiver for radiocarbon dates. palynology, because absolute pollen numbers for an individual genus, corrected for deposition rate of sediments, indicate the real change, or the extent of the reduction or increase of each type from one level to another (Davis and Deevey, 1964; Tsukada, 1966). The author's acceptance of APF as an indicator of ecology, a view with which Deevey (1965) agrees, will be supported by interpretations of paleoecologic conditions in Japan. The absolute number of pollen grains in sediments is controlled by the sedimentation rate and by the pollen productivity of the surrounding vegetaticn, both of which may be highly variable in different climatic regions or in the same locality at different times (Deevey, 1955; Tsukada, 1958a; Faegri and Iversen, 1964; and others). Fossil pollen studies first showed a clear difference in pollen density between well-humified and less-humified peat horizons bordering recurrence surface RY (rekurrensyta). To obtain a clearer comparison the APF is considered together with interrelated problems of sediment stratigraphy, recurrence surface, and climatic conditions. METHODS-For the APF estimation, after extraction of fossil pollen by the standard treatment of 10% KOH and acetolysis, pollen grains