Fagus crenata and F. japonica (Fagaceae), both endemic to Japan, are representative trees of Japanese temperate deciduous broad-leaved forests. To examine the development processes of their dominant forests, we studied the morphology of fossil beech leaves and their occurrence from the Plio-Pleistocene strata in Japan. In an Early Pleistocene leaf fossil assemblage of ca. 1.65 Ma obtained from the Sayama Formation of the Kazusa Group in the Sayama Hills, western Tokyo, beech leaves accounted for ca. 40% of the fossil leaves. Morphological features of their venation and leaf margins showed co-occurrence of three beech species, F. crenata, F. japonica, and F. stuxbergi, in the fossil assemblage, among which F. crenata was the most dominant, accounting for 22.3 % of the leaves of tree taxa. This assemblage clearly represents the oldest fossil evidence of the modern Japanese beech forest dominated by F. crenata and F. japonica. Considering their present distribution, we assumed that, around the Kanto sedimentary basin, F. stuxbergi together with F. japonica grew with evergreen broad-leaved trees at lower altitudes, whereas F. crenata grew with F. japonica and other deciduous broad-leaved trees at higher altitudes.

View full abstract

Pollen and charcoal analyses were performed in a sediment core (BP09-6) collected from the deepest area of Beppu Bay, Japan. An accurate age-depth model for the core was constructed using the wiggle-matching method. Pollen grains of Castanea, Castanopsis, and Lithocarpus that are difficult to identify with an optical microscope were identified using a scanning electron microscope. The analyses indicated that lucidophyll forests composed mainly of Quercus subgenus Cyclobalanopsis trees and Castanopsis cuspidata were predominant from 600 BC to AD 1200. These forests declined sharply after a fire event that occurred at AD 1200, indicated by a peak in the amount of macroscopic charcoal fragments in the core, and afterwords most forests in the catchment area of Beppu Bay disappeared due to increased human activities such as fires, logging, and farming. Until the first half of the Edo period, the remaining vegetation was a secondary forest comprising pine, oak, and chestnut trees, as well as light-demanding herbaceous vegetation such as grasses, moxa, and bracken. After approximately AD 1750, i.e., the latter half of the Edo period, pine forests formed in locations devastated by afforestation and natural regeneration. Then, Cryptomeria japonica plantations increased by further forestation.

View full abstract

The paleoenvironment of the Late Paleolithic in the Shimosa upland was revealed by radiocarbon dating and pollen analysis of Last Glacial sediments in a 25 m boring core obtained in Ninosawa, a branch valley of the Murata River system dissecting southwestern Shimousa upland. Organic silt and peat layers at 23.50 to 23.30 m deep and a shell at 23.00 m deep were dated to before 50,000 and 45,900–44,800 years ago, respectively. Pollen analysis indicated that wetland forests of Alnus probably spread in the lowland and that forests of Betula and such coniferous trees as Abies, Tsuga, and Picea spread on the surrounding upland at the beginning of MIS-3 or around MIS-4.

View full abstract