An outline of Quaternary development of Fagus forest in China: palynological and ecological perspectives

Abstract

Summary China is abundant in beech species. Five of ten species from the genus Fagus are distributed in southern China. Beeches are confined to the subtropical zone and mixed with evergreen trees, deciduous broad-leaved trees and conifers in China, which is quite different from North America, Europe and Japan. Fagus was distributed much further north during the late Tertiary in China. Even in Northeast China where the current vegetation is mixed conifer-deciduous broad-leaved forest, Fagus species were co-dominants at that time. During the early Quaternary, Fagus declined and even disappeared in northern China, but expanded in western Fujian Province in subtropical southern China. During the middle Pleistocene, Fagus was observed to expand in some sites, such as in northern and central Taiwan Island. The Last Glacial caused Fagus to move downward from mountainous areas, but expansion of Fagus still happened in eastern Fujian Province. Low values of Fagus pollen occurred in subtropical China during the early Holocene. It expanded in Fanjingshan, Guizhou Province, during the Holocene megathermal, and in Shengnongjia, the center of the subtropical China, after about 3800 BP. Warmth and humidity conditions were both critical to the development of Fagus forests. In comparison with other broad-leaved tree species, Fagus has a requirement for medium warmth and medium to high humidity. Only under a suitable warmth and humidity combination did Fagus become dominant, leading to a limited expansion of Fagus in some mountainous areas during the Quaternary period. In Japan, Fagus instead of Quercus spread northward after the Last Glacial due to the more humid climate. In Europe and North America, several explanations, such as decreased seasonality, human disturbance, interspecies competition and change of fire intervals have been suggested for Fagus migration. With the development of monsoon after the late Tertiary, precipitation declined and climate became more continental in northern China, preventing the northward migration of Fagus to temperate China. As a shade-tolerant species, the low regeneration ability of Fagus in forests with low coverage in the temperate zone might be an additional reason.