Salinity tolerance after seawater immersion treatment was surveyed for 20 tree species commonly found in coastal areas of western Japan to classify them as alternatives to Pinus thunbergii predominantly composing coastal disaster reduction forests. First, the Fv/Fm values and the number of fallen leaves were monitored for 10 saplings planted in 10.5 cm pots with horticultural soil, including three control saplings, of each species for 50 days after the seawater treatment. Then, their recovery or declining process was observed for seven months. The behavior of saplings after the seawater treatment was diverse for each species, ranging from no change for P. thunbergii to immediate death within six days for Aphananthe aspera. Cluster analysis detected three groups: 1) salinity-tolerant species comprising P. thunbergii and three shrubs Eurya emarginata, Rhaphiolepis indica var. umbellata, and Euonymus japonicus; 2) six salinity-sensitive species such as Morella rubra and Castanopsis sieboldii; and 3) 10 intermediate species including arboreal broad-leaved evergreen trees such as Cinnamomum camphora, Litsea coreana, and Elaeocarpus sylvestris var. ellipticus. Electrical conductivity of leaching water from the bottom of sapling pots was still significantly higher than the pretreatment value on the 50th day after the treatment, therefore the saplings appeared to be exposed to salinity stress throughout the experiment period. It could be important to select sites with a relatively lower risk of seawater immersion due to storm surges, such as inland and elevated sites, when installing arboreal broad-leaved trees in coastal disaster reduction forests as an alternative to P. thunbergii.
There are many questions on management method of old artificial sawara cypress (Chamaecyparis pisifera) stands whose age are almost 100 years old because they are rare compared with sugi (Cryptomeria japonica) and hinoki (Chamaecyparis obtusa) stands. Three plots, Shakujo1, Shakujo2, and Tsukino-ore, were selected in 2005 and total cruises were conducted three times in 8 years to analyze survival and growth. Thinning records could not be found for Shakujo1 and Shakujo2. The density of sawara cypress in Shakujo1, Shakujo2, and Tsukino-ore was 586 ha-1, 1,067 ha-1, and 450 ha-1, respectively, and mean diameter at breast height were 35.5 cm, 30.4 cm, and 47.8 cm, respectively. All sawara cypress trees were classified into five grades. Although the lowest grade class ratio was high in Shakujo1 and Shakujo2 (35% and 47%), it was low in Tsukino-ore (18%) because cleaning cutting was conducted. The death rate in 8 years was 2.4%－4.5%. Dead trees were found only in the lowest grade class in the three plots. Tree cankers were found on 69.5% and 48.7% of sawara cypress trees in Shakujo1 and Shakujo2 but 4.2% in Tsukino-ore. Thus, it should be concluded that thinning might urge growth of diameter, prevent canker damage from spreading, and effectively maintain stand soundness.
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.