Takuya Hiroshima

Strategy for implementing silvicultural practices in Japanese plantation forests to meet a carbon sequestration goal

The strategy for implementing silvicultural practices in Japanese plantation forests was examined to achieve a carbon uptake of 13.0 Mt-C year−1, which was capped by the Marrakesh Accords, during the first commitment period, 2008–2012. The plantation forests that implemented silvicultural practices in the period 1990–2012 (FM plantation forests) were identified in compliance with the hypothesized identification rules, and carbon uptake in the forests was estimated using a simple model composed of simulation and optimization components on the assumption that whole plantation forest is classified into only two groups. Furthermore, parametric analysis was conducted to investigate the relationships among three factors: (1) the average annual harvesting volume (including thinning) in plantation forests during the first commitment period, (2) the total area of FM plantation forests in 2012, and (3) the average annual amount of carbon to be sequestered in FM plantation forests during the first commitment period. The results imply that young stands have to be prioritized in implementing silvicultural practices under any harvesting plan and carbon sequestration goal, and that FM plantation forests sequestered 8.0–10.5 (Mt-C year−1) carbon in inverse proportion to the harvesting volume of 21.0–14.0 million m3 year−1 (log volume), assuming that most of the plantation forests were incorporated into them.

A Growth Prediction System for Local Stand Volume Derived from LIDAR Data

Recent advances in light detection and ranging (LIDAR) technology have enabled the estimation of valuable canopy parameters (e.g., crown diameter, leaf area, and canopy structure) that are difficult to obtain through in situ surveys. The objective of this study was to assess the utility of LIDAR-derived measurements of crown and growth parameters to model and predict the growth of sugi (Cryptomeria japonica) stands located in the University of Tokyo Forest, Chiba Prefecture, Japan. Initially, we confirmed that crown lengths and widths of trees in stands of various densities obtained from LIDAR data correlated with those measured in situ. Then, we developed a crown growth model from repeated LIDAR measurements of stands, suggesting that LIDAR data are adequate for this purpose, and indicating that crown surface area and tree volume growth were linearly related (R2 = 0.90; p < 0.01; RMSE tree volume < 0.02 m3). The model also provided robust predictions of the volume growth of local forests in 10 × 10 m plots based on LIDAR-derived estimates of crown surface areas. Future work should test the applicability of this growth model to facilitate practical forest management.

Calculation of yields on a national level by combining yields of each prefecture using the Gentan probability

The purpose of this study was to calculate the harvesting volumes on a national level by combining yields of each prefecture using the Gentan probability. The calculation was conducted as follows. First, the Gentan probabilities were estimated for the 22 prefectures that had reliable harvesting data by the maximum likelihood method. Second, these prefectures were clustered into 3 groups by the agglomerative hierarchical clustering method based on the estimated Gentan probability patterns, and then the synthesized Gentan probabilities were estimated for each cluster from the aggregated stand areas and harvested areas of prefectures which belonged to the same cluster. Third, the other 25 prefectures without reliable harvesting data were classified into the preceding 3 clusters by discriminant analysis with socioeconomic explanatory variables. Finally, harvesting area and volume were calculated for each prefecture based on the estimated Gentan probabilities: The former 22 prefectures employed the Gentan probabilities derived from their own harvesting data while the latter 25 prefectures employed the synthesized Gentan probabilities corresponding to their cluster number classified. The validation results showed that the supposed method caused the percentage error of 2.11% in total of all 47 prefectures towards the corresponding forestry statistics in a log volume. It was sufficiently precise compared with the previous prediction results of around 20% percentage error on a national level.

Estimation of the Gentan probability using the price of logs in private plantation forests

The Gentan probability is defined as the probability that a newly planted forest stand will be harvested at a certain age. In this study, the Gentan probability was estimated using the price of logs, in accordance with the notion that the probability is influenced by economic factors. In order to estimate the Gentan probability, we adopted a probability density function based on the forest owners’ decision-making process, which consisted of a decision criterion, a decision criterion function and a criterion threshold. The price of logs was employed for the criterion, and the decision criterion function was defined as the value of the forest stand based on the price of logs. Moreover, the mechanism of changes in the threshold was formulated based on the random walk concept. The parameters of the suggested Gentan probability were calibrated to fit the harvesting tendencies observed in the past. Finally, the Gentan probability distributions estimated using the prices of logs over the past 20 years were compared with those estimated using felling age means and variances. The two distributions were closely correlated during most years. The proposed Gentan probability model takes advantage of short-term yield predictions such as an analysis of forest owners’ reactions to the current price changes.

Calculation of commercial thinning volumes in 47 prefectures in Japan

ABSTRACT The Forest and Forestry Basic Plan set Japan’s domestic timber supply goal of 32 million m3 by 2020. To achieve the goal, a large increase in thinned timber production will be required. The purpose of this study was to calculate and understand the current situation of commercial thinning volumes in all 47 prefectures as a basis for projecting future changes in thinned timber production. First, thinning records at prefectural level were obtained. Thinning areas by age classes and commercial thinning ratios were predicted for those prefectures without available thinning records using clustering, discriminant analysis, and logistic regression. A thinning yield table was also constructed for each prefecture, based on the mean volume of six tree species assuming certain thinning types, intensity, and timings. Finally, the commercial thinning volume was calculated for each prefecture by multiplying thinning area, thinning volume per unit area in a yield table, and commercial thinning ratio. Graphs of commercial thinning volumes suggested that Hokkaido and Kumamoto had particularly high thinning volumes, Akita, Nagano, Shizuoka, Oita, Miyazaki, and Kagoshima also had relatively high volumes. The calculation results in prefectures were considered reasonable, based on calibration and validation that reflected the regional difference in thinning trends.