Application of a modified rate equation to the acetylation of wood

A modified rate equation, in which the diffusion of reagent was taken into consideration, was proposed and applied to results reported previously for the acetylation of wood. The equation was fitted more successfully to the prolonged as well as the early stage of the reaction than a common first-order rate equation. Although the conclusions were virtually unchanged, the reliability was enhanced because reaction parameters such as the rate constant, ultimate extent of the reaction, and activation energy calculated for the modified equation were based on much more data than those reported previously. The equation proposed here may be applicable not only to acetylation but to other chemical modifications of cellulosic materials in heterogeneous systems.     

A mathematical model for generating land-use allocation alternatives for agroforestry systems

Agroforestry has been considered a viable land-use system particularly in the tropical regions. In developing or designing agroforestry systems, various concerns have to be addressed namely: (1) economic; (2) biological and physical; and (3) silvicultural and ecological considerations. This paper addresses these concerns from an interdisciplinary perspective. A land-use allocation model which ensures the simultaneous consideration of these concerns is proposed.     

A variance-covariance structure to take into account repeated measurements and heteroscedasticity in growth modeling

This study proposes a within-subject variance-covariance (VC) structure to take into account repeated measurements and heteroscedasticity in a context of growth modeling. The VC structure integrates a variance function and a continuous autoregressive covariance structure. It was tested on a nonlinear growth model parameterized with data from permanent sample plots. Using a stand-level approach, basal area growth was independently modeled for red spruce (Picea rubens Sarg.) and balsam fir [Abies balsamea (L.) Mill.] in mixed stands. For both species, the implementation of the VC structure significantly improved the maximum likelihood of the model. In both cases, it efficiently accounted for heteroscedasticity and autocorrelation, since the normalized residuals no longer exhibited departures from the assumptions of independent error terms with homogeneous variances. Moreover, compared with traditional nonlinear least squares (NLS) models, models parameterized with this VC structure may generate more accurate predictions when prior information is available. This case study demonstrates that the implementation of a VC structure may provide parameter estimates that are consistent with asymptotically unbiased variances in a context of nonlinear growth modeling using a stand-level approach. Since the variances are no longer biased, the hypothesis tests performed on the estimates are valid when the number of observations is large.     

Allometric model of the Reineke equation for Japanese cypress (<Emphasis Type="Italic">Chamaecyparis obtusa</Emphasis>) and red pine (<Emphasis Type="Italic">Pinus densiflora</Emphasis>) stands

An allometric model that explains the mechanism of the difference in the slope of the Reineke equation (A) among species was proposed based on the allometric relationships of mean tree height (H) to quadratic mean diameter D (H ∝ D ^θ ) and stand density N (H ∝ N ^δ ), i.e., A = θ/δ. The proposed model was fitted to Japanese cypress (Chamaecyparis obtusa Endl.) and red pine (Pinus densiflora) stands. The allometric exponents θ and δ were, respectively, 0.8995 and −0.5000 for cypress and 0.8612 and −0.6619 for pine. The difference between cypress and pine was significant for δ but not for θ. Inserting the exponents into the model resulted in predicted slopes of −1.7991 for cypress and −1.3011 for pine. The difference in the slope of the Reineke equation between the two species was produced by characteristics related to the tree crown, rather than characteristics related to stem slenderness. The proposed model enables us to estimate the slope of the Reineke equation from commonly measured stand attributes, such as mean tree height and quadratic mean diameter. Therefore, the proposed model is expected to be practical and convenient for estimating the slope of the Reineke equation and for explaining the mechanism of its variation among species. The model should be also accepted as a generalized model of the stand density versus quadratic mean diameter relationship, whereas the original Reineke equation should be seen as a specific case of this model.     

尾叶桉材积蓄积计算公式初探

从雷州林业局几个点收集２～１１年生的尾叶桉生长资料和４９株解析木材料，用数学回归方程推导出二元材积公式和蓄积公式，经验证，其精确度可靠     

单株平衡法的建立

单株平衡法的建立孙长忠，黄宝龙（西北林学院林学系杨陵７１２１００）（南京林业大学南京２１００３７）关键词黄土高原，蒸腾量，蒸发量，单株平衡法，单株平衡方程，蒸发偏量在黄土高原地区，水分因素对植物生长及生存具有强烈的限制作用。研究植物生长与环境水分条件...     

Numerical experiments of watershed-scale soil water movement and bedrock infiltration using a physical three-dimensional simulation model

Numerical experiments of soil water movement and bedrock infiltration based on a simplified simulation method were conducted to analyze watershed-scale rainfall-runoff processes. To verify the model accuracy, it was applied to a Minamitani watershed (0.45 ha). The simulation was performed with 2.5-m space grids horizontally and five cells vertically. Results of long-term calculation of this model proved that this simulation model is robust and demonstrated good computational water mass conservation. Calculation results showed the best agreement with observed hydrographs and the number of groundwater levels simultaneously when laboratory-tested soil hydraulic characteristics for topsoil were used and infiltration into bedrock was included in numerical calculations. Numerical experiments show that bedrock infiltration generated a stable base flow and suppressed the secondary discharge peak. The reproducibility achieved by observed soil hydraulic characteristics with the assumption of bedrock flow demonstrates the effectiveness of the simulation model used in this article for analyses of watershed-scale soil water movements.     

Comparison of structural diversity of tree-crop associations in Peripheral and Buffer zones of Gachabari Sal forest area, Bangladesh

The structural diversity of different tree-crop associations were studied at Gachabari Sal forest area of Madhupur Garh on Buffer and Peripheral Zone during 2006. The total density, basal area of trees in the Buffer and Peripheral Zone were 155.5 trees·hm^-2, 795.4 trees·hm^-2 and 3.9 m^2·hm^-2, 5.8 m^2·hm^-2, respectively. No regeneration and natural trees were found in Peripheral Zone and the Zone is totally occupied by exotic species where the Buffer Zone comprised of both natural and exotic trees. The Peripheral Zone belonged to younger and smaller trees whereas the Buffer Zone belonged to mixture of smaller, taller, younger and mature trees simultaneously. For the practicing of different agroforestry systems both Zones have lost their original characters of Sal forest.     

L35等杨树新品种造林当年年生长节律研究

利用Logistic方程对4个黑杨派杨树无性系的1a生林木的树高、胸径的年生长节律进行拟合。结果表明：利用Logistic方程拟合效果显著，相关系数皆在0．90以上。并以此将各无性系的年生长过程分为成活期、生长前期、速生期和生长后期4个时期，年生长量在后3个时期表现出明显的“慢—快—慢”的节律，其中速生期内的树高生长量占总生长量的比率平均为66．4％，胸径生长量占总生长量的比率平均为64．0％。树高比胸径进入速生期早且结束晚，速生期持续时间长。对各个生长时期林木的生长特点进行了分析，探讨了林木的年生长规律，为加强林木生产管理、提高林地的生产力，提供了理论依据。