Changes on ecophysiological publication number on <i>Cryptomeria japonica</i> and <i>Chamaecyparis obtusa</i> and their environmental and social background after 1950

<p>To elucidate the history of ecophysiological research and its environmental and social background, we analyzed the literature published over the past seven decades about ecophysiological features of Japanese cedar and cypress. The literature was widely classified into six categories: biomass, photosynthesis and respiration, nutrient contents in the tree, water use traits, wood traits, and others. We calculated number of research at 5-year intervals. According to the time period, the number of published articles peaked in 1975-1979, declined in 1980-1984, increased again in 1985-1989, and continued to decline gradually until 2020. Our analysis suggests that the first decline may have been due to the end of the period of enlargement of planting forest by conifer, which promoted intensive forest fertilization experiments and led to many articles being published about tree nutrient content. The International Biology Program (1965-1974) also largely impacted this situation, specifically as research on biomass peaked during the 1970s. The next increase in publication from 1985 to 1989 was due to the development of measuring devices as well as the increased recognition about the physiological traits of trees and their indispensable role in combating acid rain and climate change. The number of research written in English has increased since the 2000s, and the international dissemination ability also grown. A relationship was also established between the regions in which most of the research was conducted and the locations of the main research groups. This study demonstrated that the numbers of articles and the target research topic have evolved over time and that these changes were driven by social and environmental factors, such as the period of enlargement of planting forest by conifer and measures against climate change.</p>