Warm-Temperate Deciduous Forests: Concept and Global Overview

The zonal vegetation of [humid] warm-temperate regions is normally considered to be evergreen broad-leaved forest, such as the “laurel forests” of East Asia, southern Brazil, and much of New Zealand. Observing the vegetation of Japan and other parts of East Asia, however, Kira noted in 1949 that some deciduous Quercus species do not occur in either the cool-temperate (deciduous) or the subtropical (evergreen) zone and eventually proposed the concept of warm-temperate deciduous forest, composed especially of Quercus species. These species occur in the drier climates of interior Honshū, especially around Nagano, where summers are warm enough but winters are too cold for evergreen broad-leaved forest. This concept also fits parts of middle-eastern China and lowland Korea, where most of the same Quercus species also occur. Analogous warm-temperate deciduous forests beyond Asia appear to include, inter alia, the Quercus-Carya forests of interior southeastern North America and the Quercus pubescens forests of southern Europe. In East Asia, some main deciduous species are Quercus variabilis, Q. serrata, Q. aliena and Q. dentata, all occurring on mesic to dry sites. These species also form the canopy of secondary deciduous forests that are eventually replaced by the zonal warm-temperate evergreen broad-leaved (laurel) forests. In eastern North America, some Quercus and other deciduous taxa (including Fagus) have wide north-south ranges, but deciduous Q. falcata, Q. nigra, and others have distinctly southern ranges. This southern area is in the warm-temperate zone and has mean winter temperatures significantly higher than in East Asia (albeit with unusual lower extremes). Warm-temperate deciduous forest analogs around the Northern Hemisphere can be identified from climatic considerations but also from phytosociological analysis (and ordinations) based on relevé data, suggesting that this is a consistent sub-zonal forest type.