Tomiyasu Miyaura

Relationships of tree height and diameter at breast height revisited: analyses of stem growth using 20-year data of an even-aged Chamaecyparis obtusa stand

Stem diameter at breast height (DBH) and tree height (H) are commonly used measures of tree growth. We examined patterns of height growth and diameter growth along a stem using a 20-year record of an even-aged hinoki cypress (Chamaecyparis obtusa (Siebold & Zucc.) Endl.) stand. In the region of the stem below the crown (except for the butt swell), diameter growth rates (ΔD) at different heights tended to increase slightly from breast height upwards. This increasing trend was pronounced in suppressed trees, but not as much as the variation in ΔD among individual trees. Hence, ΔD below the crown can be regarded as generally being represented by the DBH growth rate (ΔDBH) of a tree. Accordingly, the growth rate of the stem cross-sectional area increased along the stem upwards in suppressed trees, but decreased in dominant trees. The stem diameter just below the crown base (DCB), the square of which is an index of the amount of leaves on a tree, was an important factor affecting ΔDBH. DCB also had a strong positive relationship with crown length. Hence, long-term changes in the DCB of a tree were associated with long-term changes in crown length, determined by the balance between the height growth rate (ΔH) and the rising rate of the crown base (ΔHCB). Within the crown, ΔDs were generally greater than the rates below the crown. Even dying trees (ΔD ≈ 0 below the crown) maintained ΔD > 0 within the crown and ΔH > 0 until about 5 years before death. This growth within the crown may be related to the need to produce new leaves to compensate for leaves lost owing to the longevity of the lower crown. These results explain the different time trajectories in DBH–H relationships among individual trees, and also the long-term changes in the DBH–H relationships. The view that a rise in the crown base is strongly related to leaf turnover helps to interpret DBH–H relationships.

A before and after comparison of the effects of forest walking on the sleep of a community-based sample of people with sleep complaints.

BackgroundSleep disturbance is a major health issue in Japan. This before-after study aimed to evaluate the immediate effects of forest walking in a community-based population with sleep complaints.MethodsParticipants were 71 healthy volunteers (43 men and 28 women). Two-hour forest-walking sessions were conducted on 8 different weekend days from September through December 2005. Sleep conditions were compared between the nights before and after walking in a forest by self-administered questionnaire and actigraphy data.ResultsTwo hours of forest walking improved sleep characteristics; impacting actual sleep time, immobile minutes, self-rated depth of sleep, and sleep quality. Mean actual sleep time estimated by actigraphy on the night after forest walking was 419.8 ± 128.7 (S.D.) minutes whereas that the night before was 365.9 ± 89.4 minutes (n = 42). Forest walking in the afternoon improved actual sleep time and immobile minutes compared with forest walking in the forenoon. Mean actual sleep times did not increase after forenoon walks (n = 26) (the night before and after forenoon walks, 380.0 ± 99.6 and 385.6 ± 101.7 minutes, respectively), whereas afternoon walks (n = 16) increased mean actual sleep times from 342.9 ± 66.2 to 475.4 ± 150.5 minutes. The trend of mean immobile minutes was similar to the abovementioned trend of mean actual sleep times.ConclusionsForest walking improved nocturnal sleep conditions for individuals with sleep complaints, possibly as a result of exercise and emotional improvement. Furthermore, extension of sleep duration was greater after an afternoon walk compared to a forenoon walk. Further study of a forest-walking program in a randomized controlled trial is warranted to clarify its effect on people with insomnia.

Geographic variation in nut size of Castanopsis species in Japan

The environmental conditions affecting the geographic variation in nut size of the Castanopsis species in Japan were examined. The mother trees having a relatively large nut tended to dominate in the geographically marginal area of the distribution range in Japan, i.e. the Japan Sea, Kanto, and Ryukyu areas, whereas in the central area, i.e. the Pacific area, mother trees having a relatively small nut occurred. We attempted an adaptive explanation, proposing that mother trees with large nuts have higher inclusive fitness than those with small nuts in unfavorable habitats. The Japan Sea area features large amounts of snow fall and low temperatures. The Ryukyu area is insular and is characterized by high temperatures. Within the Pacific area, mother trees with relatively large nuts were abundant at both higher and lower parts of the altitudinal range. We infer that environmental conditions in marginal areas, in terms of both horizontal and vertical distribution, favor mother trees having large nuts. However, in the marginal Kanto area, the cause of the absence of mother trees having relatively small nuts was independent of the environmental conditions. The geographic variation in nut size of Castanopsis species is not always explained by environmental factors.

Effect of Japan Sea Climate on Geographic Distribution of Castanopsis sieboldii and C. cuspidata

The geographic distributions ofCastanopsis sieboldii andCastanopsis cuspidata overlap each other on the Pacific coast of Japan, but on the Japan Sea coastC. sieboldii tends to dominate at similar temperatures. The authors attempted to explain this phenomenon by analyzing the effects of climatic factors. Nuts were collected from the Pacific and Japan Sea coasts of the Kinki and Chugoku districts, and the nut characteristics and the number of layers of epidermis in the leaves of the seedlings were investigated. The distribution ofC. sieboldii andC. cuspidata was satisfactorily explained by a multiple regression equation that was developed using three climatic factors: maximum snow depth in winter, lowest temperature in the coldest month, and annual mean temperature, out of fourteen such factors that were considered. The estimated distribution ofC. sieboldii andC. cuspidata from the multiple regression equation agreed with 66.2% of the actual observations.

Interannual variability of leaf area index of an evergreen conifer stand was affected by carry-over effects from recent climate conditions

Despite the relevance of leaf area index (LAI) to forest productivity, few studies have focused on the interannual variability of LAI of an evergreen stand and its relationship with stand growth and meteorological factors. We estimated the change in LAI of an evergreen conifer (Chamaecyparis obtusa) stand over 19 years from a dataset using allometric methods. The LAI varied between 7.1 and 8.8 m2 m−2, with a 95% confidence interval of <1.1 m2 m−2 over the 19 years. This LAI range was maintained such that the gradual increase in leaf area (LA) of the largest trees counterbalanced the gradual loss in LA of the smallest trees. Meanwhile, more trees showed a temporary decrease in LA in years with low summer precipitation. The LAI and current-year mean temperature for July and August (TJA) were weakly correlated, whereas the correlation coefficient increased (r = 0.93) when LAI was correlated with the moving average TJA over the previous 6 years, which agreed with the estimated turnover time of canopy foliage. The annual stem biomass growth rate was significantly positively correlated with summer precipitation, but not with LAI. These results will be useful for refining models in studies on forest growth and global climate change.

An examination on the site–family interaction of tree height of open-pollinated families of hinoki (Chamaecyparis obtusa) plus trees in the Kansai Forest tree breeding region

Stability analyses to evaluate site–family interaction for tree height at 15 years old were conducted in trials of open-pollinated families of hinoki (Chamaecyparis obtusa Endl.) plus trees established in the Honshu and Shikoku area of the Kansai Forest tree breeding region, Japan. The Honshu area included 103 sites (226 families), and the Shikoku area included 27 sites (62 families). Analyses of variance indicated that the interaction between site and family was not significant in the Honshu area, whereas in the Shikoku area the interaction was significant. The stability analyses regressed the family–site means against site means. The linear regression analysis was carried out using the data for 164 families that were tested at five or more test sites from the 130 test sites. Approximately 93% of families had values of linear regression coefficient that were not significantly different from unity. These results suggest that almost every open-pollinated family of hinoki plus trees have average stability and are equally well adapted to good and poor sites. The differences in the reaction of a family to site productivity are not the main causes of the interaction.