In humid regions of the western Pacific, there are two geographically discontinuous forest zones of conifer-dominated forests, i.e. boreal zone and temperate-to-tropical zone, separated by deciduous broadleaf forest zone with warm summer and cold winter. Boreal conifer forest is characterized by continental climate with short summer and cold winter (Kira’s warmth index, WI < 45°C and coldness index, CI < –15°C), whereas 'temperate-to-tropical conifer-mixed forests' in both hemispheres are characterized by oceanic, moderate climate lacking severe winter (WI <144°C and CI > –15°C). Boreal conifer forests are distributed at high latitudes or altitudes in Japan. Temperate-to-tropical conifer-mixed forests’ occur in a narrow belt on the Pacific Ocean side in Japan, at high altitudes in Taiwan, tropical Southeast Asia and New Guinea, and in temperate zones of Tasmania and New Zealand. It appears that relatively cool summer (or year-round low temperature on tropical mountains) limits the growth of evergreen broadleaf trees while mild winter (or the absence of winter on tropical mountains) gives the competitive advantage to conifers over deciduous broadleaf trees, leading to conifer dominance in the temperate-to-tropical conifer-mixed forests.