The ecoregion covers an area of 138,300 square kilometers (53,400 sq mi) on the Pacific (Taiheiyo) side of the islands of Honshu, Shikoku, and Kyushu.

[2] The ecoregion is home to Japan's largest cities, including Tokyo, Yokohama, Osaka, and Nagoya.

The influence of the Japan Current creates a humid climate with mild winters and a long growing season, which nurtured evergreen broadleaf forests.

Trees with origins in temperate Eurasia include species of evergreen oaks, Castanopsis, Salix pierotii, Picea jezoensis, Pinus thunbergii, Pinus pumila, Prunus nipponica, Tilia amurensis, Betula dahurica, Betula pendula, Pinus koraiensis, Picea obovata, Abies sibirica, Quercus acutissima, Quercus mongolica, Quercus glauca, Prunus serrulata, Prunus padus, Salix babylonica, Acer palmatum, Populus tremula, Ulmus davidiana, and Ulmus pumila.

[3] Native mammals include the Sika deer (Cervus nippon) and Japanese macaque (Macaca fuscata).