The thinning effects and the stand density level were analyzed from ecological viewpoints using continuous forest inventory data in order to apply the growth model of System Yield Table to lower stand densities. Growth simulations under different stand density conditions showed that the total yield volume changed little if the cutting age is long enough. This result suggests the soil and water protection forests had better be managed in lower density with long rotation for not only environmental purposes but also timber production.
For the grouped growth data sampled individually with repeated measures, two types of growth curves can be simultaneously estimated by using a multivariate non-linear regression model with random effects. One is the average growth curve for the group, and the other is each individual growth curve within the group. With the use of forest stand growth data we elaborate methodological steps for estimating the average growth curve as well as an individual growth curve. A confidence interval of the average growth curve for the group is also determined. We apply a generalized non-linear mixed effects model to the analysis, which is one of multivariate non-linear regression models with random effects.
The index "l/d" was called "k-ratio". "l" was the distance between a point on a stem and the top of the stem, and "d" was the diameter of the stem at the point. Next, uniform distribution of k-ratio at breast height was derived from a Hinoki stand, and a height growth curve and "k=a+bl" was derived from a sample tree which stem was analyzed. And the formulas were integrated to a stand-model, which was composed of functions about stem curve of Behre formula, stem volume, and maximum stand density. At the stand age 66, the stem volume of the model was 10% lower than the one of real stands. As a result, the model could describe a total stands with each individual stand, and it was to be improved.
Considering the competition among individual trees and some artificial effects on surrounding tree growth environments by pre-commercial, commercial thinning and self-thinning, each tree grows not only following its own growth trend but also with some structural change in growth pattern. In this paper, we propose a statistical method to investigate whether a structural change occurs in the growth of a tree. Using tree diameter growth data without any record on the management treatments, we present how the proposed method can be used. The proposed method is based on statistical testing under the null hypothesis supposing no change against the alternative hypothesis supposing the existence of the change.
In this paper, we analyzed the structural change in log production during the period. First, Cobb-Douglas production functions were estimated for each year over 1970-2000 using cross-section data. Then, we derived the technical progress ratio and looked into the changes in the production function coefficients of labor, forestry machine and highly efficient forestry machine. As a result, it is found that the technology of Japanese log production has been increasingly characterized by the increasing returns to scale. During the 1990s, labor had the highest average contribution rate. Although the contribution rate of highly efficient machine was in low level, it was increasing and the effects of the productivity advance were around I 00% with some regions of more than 100% of the ratio, while the values of labor and forestry machine leveled off or decreased. Thus it is considered that the introduction of highly efficient machines had some eiTect in substituting decreasing labor.
We analyze effects of trade liberalization on sustainability of forest stand management through a stochastic control model to capture forest owners' harvest decision process under log price stochasticity. We first investigate how change in the amount of the drift and volatility term of price dynamics affects the minimum threshold price level to sustain forest stand management. As a preceded example, the beef price data are used to observe an influence of trade liberalization on the drift and volatility term of the beef price dynamics. Considering the results obtained, simulation analysis is conducted to reveal effects of trade liberalization for timber products on forest stand management. Our experimental results show the following. Introducing trade liberalization results in increase in the price volatility over the short term first. This change then leads to reduction of the minimum threshold price level to sustain the forest stand management. As the minimum threshold price level decreases, we can expect the wider gap between the actual market price and the induced threshold price, which stimulates more timber product supply. Should this occur, the market price would turn to be lower. This change of the market price results in a decreasing trend of the price over the time horizon. Since the decreasing trend of the price pushes the minimum threshold price level up as an inverse effect of the volatility, we expect the more probability of disappearance of timber suppliers from the market.
In the Second Commitment Period of the Kyoto Protocol, it is expected that full-carbon-accounting (FCA) would be adopted as a standard method for quantifying forest carbon sequestration. To conduct FCA at broad scales, numerical analyses of carbon dynamics through atmosphere, vegetation, and soil, with appropriate process-based model, should be effective, in conjunction with inventory and remote sensing studies. In this study, using an ecological carbon cycle model, a numerical simulation was conducted to retrieve temporal change in carbon budget including not only woody stem but also root and soil organic matter; based on the result, discussions were made on the applicability of model approach to FCA operation.
Acacia species have been widely planted for the purpose of industrial plantations in Southeast Asia. Among them, Acacia mangium was planted as one of promising fast-growing tree species in a large scale area not only for industrial use, but also for remediation of forest degradation in tropics. Recent experiments show basic conditions for successful plantation of Acacia mangium in tropics as well as the silvicultural treatments. From a viewpoint of CDM (Clean Development Mechanism) on plantation projects for global warming prevention, Acacia mangium plantation is expected to have efficient and profitable results by constructing the pulp-chip and log production system. In this paper, the growth characteristics of Acacia mangium in Peninsular Malaysia is discussed. Case studies on Acacia mangium plantations in Peninsular Malaysia are also conducted in order to analyze the growth performance of Acacia mangium and construct a growth model and yield table for Acacia mangium.