Phytosociology of the Beech (Fagus) Forests in East Asia

Abstract

Speciation of beech (genus Fagus) in East Asia has been intensive and beech forests are widely, though disjunctly, distributed within Japan, Korea, China and Taiwan. Beech forests lie between the evergreen broad-leaved forests in the south (lower limit) and the evergreen coniferous trees in the north (upper limit), making them a key vegetation type in East Asia. In this study, to better distinguish the features of beech forests in East Asia, we compared species composition of beech forests based on the known releves and on new releves we carried out in the field. As a result of that comparison, we were able to divide the beech forests of East Asia into three classes. Classes I and II are characterized by the abundance of deciduous flora. These 2 classes contain 4 orders, 8 alliances, 20 associations and 48 subassociations. Class III is composed of evergreen broad-leaved forest with the presence of Fagus. There are few common species among the classes, especially in China. Because of that, it is hard to describe the similarities and differences of plant communities only considering the species level. For that reason, we further compared also the genus and family composition, which were considered to have larger distribution between the different vegetation types. East Asian beech forests are characterized by genera endemic to East Asia, as well as by genera common to beech forests of the northern hemisphere. Classes I and II show a large overlapping in genus composition. Within each order, there are many characteristic genera, a fact that confirms the independence of each order. In contrast, few characteristic genera are found at the alliance level, although the frequency of genera within each alliance varies. That is not the case, however, in the association and the subassociation levels. We also compared life form composition for each vegetation unit. We found the following: (1) beech forests in East Asia always contain scrub bamboo species; (2) classes I and II contain evergreen conifers of PEN and NPEN life forms. Class I contains proportionally more deciduous flora, classified as life forms of PD, NPD, H scap and H rosul. Class III, in contrast, contains proportionally more evergreen flora, classified as life forms of PE, NPE and G rhiz. Class II contains an intermediate proportion of deciduous and evergreen floras. At the order level, the frequency of life forms for shrub and herb species is characteristic. At the alliance level there is much less difference in life form composition within each alliance. At both the alliance level and the order level, when the proportion of life forms indicative of broad-leaved forests is higher, the proportion of herbaceous life forms is lower. There are no significant differences in life form composition within each association and subassociation; a comparison of life form compositions within the lower vegetation units would not, therefore, be useful.