Optimization of forest stand management is an important basic technique to plan cutting. Convergence for a global solution is the most important point when measuring confidence. In this paper, we compared three methods, dynamic programming, random search, and full search, and examined their effectiveness. We took larch in Nagano as the object of optimization, and applied a stand density diagram as a growth model. Profits were calculated by yield rate of mass, but the value of the trees shifted with DBH. Net present value of yield was adopted as the criterion for optimizing. Separation of thinning trees was fixed every 5 per hectares in dynamic programming and random search, and every 5% in full search. Interval of thinning available age was 5 or 10 to plan length. Then we optimized those models with each method. As a result, the criterion of the full search was the highest, next was that of the random search and that of dynamic programming was the lowest. When the model in which the value of trees increased and decreased with DBH was adopted, the annual criterion of the solution for dynamic programming differed from that of the other two methods. The number of calculations for one forest stand in dynamic programming was the fewest; next was random search, and that of full search was much larger than for the other methods. So considering for number of calculations and confidence in the solution, random search was the best method under this profit model.

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The forest density management of the past, was understood and managed in terms of the yield of stem volume. When the forest is regarded as a carbon sink, we think it should be understood and managed on the basis of tree weight rather than stem volume. The implications are especially important when evaluating a forest that is not intended for timber production. In addition, the full density curves, which are common in various density control systems, are those defined by the tree weight originally. Therefore, the aim of this research is the creation of a yield-density diagram on the basis of tree weight. We surveyed a coastal black pine forest in Shonai. The slope of the full density curve was −0.507. In this study, the Y-N curves of different forest stand ages were calculated from the relationship between forest stand age and B-point. By incorporating the time axis on the yield-density diagram, it became possible to understand and evaluate the relative tree weight of forest stands. In addition, the yield-density diagram can also be applied to density management aimed at high carbon accumulation. The yield-density diagram has been modified as the next-generation approach to meet the needs of the times by using tree weight in this research.

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To evaluate the possibility of year-round planting of containerized cuttings, we compared the survival rate and current-year growth of containerized sugi (Cryptomeria japonica) cuttings planted in different seasons (December, February, May, August and October). In addition, bare-root cuttings were planted in February, and we compared the current-year growth between containerized cuttings and bare-root cuttings. The survival rate of containerized cuttings was at least 94% in all of the planting seasons, and was comparable to that of the bare-root cuttings planted in February. In addition, growth of both cuttings types was also equivalent. Although the growth of containerized cuttings planted during the growing season (May, August and October) was dependent upon the remaining length of the growing season, diameter growth tended to be smaller in cuttings planted in May. It is possible that containerized cuttings could start growing immediately after the arrival of the following spring because they had high survival rates and had already started growing if they were planted in the growing season of the current planting year. However, the planting of containerized seedlings and cuttings is a recent technique and future research assessing the optimal time for planting and supply of seedlings and cuttings needs to be undertaken.

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The cutting cultivars of Cryptomeria japonica in the Kyushu district usually consist of several different clones according to many recent reports using DNA markers. However, the genetic relationship between the cutting cultivars and genotypes within each cutting cultivar has not been studied well. Therefore, we examined clone identification and investigated the genetic relationship for major cutting cultivars in C. japonica planted in Kumamoto Prefecture Forestry Research Center using SSR markers. Clone identification using nine genomic SSRs showed that 279 individuals, representing 19 cutting cultivars, were classified into 26 genotypes. The cutting cultivars such as Measa, Ayasugi, Yabukuguri and Obiaka were clone-complex cultivars of major clones. In addition, we found the same genotypes with different cultivar names, which were presumably derived from misclassification. After excluding such suspected individuals, 19 genotypes were analyzed using 33 SSR markers (the previous nine genomic SSRs and an additional 24 EST-SSRs) to investigate their genetic relationship. Our results showed that the cutting cultivars in the Kyushu region have relatively large genetic variations and suggested multiple origins of their cultivars.

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Change in height growth of Japanese cedar was investigated within a plantation of this species which was planted in 1908, was thinned three times during the age of 45∼73 years old with various intensities, and was 104 years old at the last inventory. To test whether the height growth rate of trees should be lower after thinning operations than without thinning operations, pairs of 45-years-old trees were selected; for each pair, one tree was selected from stands with thinning operations and the other from those without thinning, with criteria that they were almost equivalent in terms of diameter and height. Among these pairs (189 in total), the pairs which showed equivalent diameter growth of constituent trees afterward were selected, and height and slenderness (height/diameter) was compared between the trees belonging to the same pair. The trees of intensively thinned stand showed lower height growth beyond the age of 60, and this tendency persisted until age of 104. The trees of moderately and lightly thinned stands showed a similar pattern during the later period. At the age of 104 year old, trees in the moderately- or intensively-thinned stands showed lower values for slenderness than those in the un-thinned stands. This was explained by both greater diameter growth and lowered height growth caused by thinning operations.

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Summarizing seven studies that measured throughfall drops in Japanese cypress (Chamaecyparis obtusa) plantation, we found positive correlation between kinetic energy of throughfall normalized by rainfall (KE_N; J m⁻² mm⁻¹) averaged in several rainfall events and crown bottom height but negative correlation between KE_N and crown length. The results suggest the increase of fall velocity of drips with increasing crown bottom height, and the increase of the opportunities that drips splash on lower layer foliage with increasing crown length. An empirical equation for estimating KE_N from crown bottom height and crown length was developed. The equation will be useful for assessing infiltration, overland flow, and soil erosion on bared forest floor in Japanese cypress plantations reflecting difference in canopy structures.

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