How biodiversity is associated with ecosystem productivity has been major concern. In this study, we aim to build and examine a framework how spatial differences in tree community are associated with stability of net primary production (NPP) across a gradient of temperature. NPP of forest can be analyzed as the product of (1) how much light is intercepted (I) and (2) how efficiently intercepted light is converted into biomass. Forest light interception can be further decomposed into light interception per unit leaf area (I/LA), the ratio of leaf are to leaf mass (LA/LM) and the amount of leaf mass (LM). Among 22 broad-leaved natural forests across Japanese archipelago, total solar radiation during the growing season declined by 50% from 20 to 5 degree of mean annual temperature, and total leaf mass declined at similar extent. NPP also declined by 50%, but this decline was not so low as expected from the declines in both solar radiation and leaf mass (i.e. 50*50=25%). Broad-leaved tree communities in colder regions had on average 50% larger leaf area for a given leaf mass than those in warmer regions, which enabled them to capture light efficiently with limited amount of leaf mass. Cross-species differences in leaf morphology (and physiology) across a range of temperature are critical to maintain large-scale stability of NPP.