Testing the suitability of the Nepal-Somers stand table projection method for Eucalyptus grandis plantations in South Africa

This study presents an application of a stand table projection method for varying stand densities of Eucalyptus grandis in South Africa. The projections of diameter at breast height (dbh) class frequencies are compatible with future values of basal area and stem number per hectare. The application requires an individual tree dbh growth function, a current stand table, and estimates of future basal area, and tree survival. The resulting stand table is adjusted by an algorithm that guarantees that the future stand table is compatible either with observed or predicted values of basal area and stem number per hectare. The results, based on a relatively small experimental dataset, are satisfactory. However, further work based on a larger dataset is required to evaluate the general suitability of the method for stand table projection of Eucalyptus grandis in South Africa, especially regarding variable site conditions. The particular contribution of this study is the fact that we were able to demonstrate the suitability of the Nepal and Somers stand table projection method for a unique dataset from a very densitysensitive Correlated Curve Trend spacing trial. We also made an attempt to present a comprehensive example of a projection to facilitate practical application of this method in the KwaZulu-Natal coastal plain of South Africa.     

稻曲病病情分级标准的研究和应用

考查了稻曲病不同曲果数在单穗上的分布。应用Ｑ型系统聚类分析,以曲果纵横径比,百曲果重,单穗实粒重,结实率,损失率为指标进行数量分类,确定了稻曲病病情分级标准,即０级,未发病：Ⅰ级,１粒曲果：Ⅱ级：３粒曲果,并利用韦伯模型描述了稻曲病病情指数和产量损失率的关系。     

华北地区油松人工林直径分布规律研究

本文利用Weibull分布密度函数对华北地区油松人工林直径分布规律进行了拟合检验与直径分布特征分析,结果表明:(1)整个调查地区油松人工林的直径分布不太合理,林分的密度需进行必要的调整,尤其是对于高密度造林的地段;(2)整个调查地区绝大多数林木的直径分布仍表现为中度偏小的径阶林木株数占多数的特点,急需进行必要的抚育间伐,以提高油松人工林质量;(3)平均胸径与Weibull分布密度函数三参线性回归分析的结果还不能充分应用于生产实践,有待于今后深入的探讨与试验。     

利用Weibull分布描述日本落叶松的直径结构

利用W e ibu ll分布对日本落叶松直径结构进行研究。根据检验结果表明:拟合效果良好,并据此建立起了a、b、c参数的预测模型。提出了日本落叶松人工林林分结构合理分布的理论参数,为合理经营日本落叶松人工林提供了科学的理论依据。     

吉林省柳河县水稻二化螟发生期预测模型的建立

在吉林省柳河县绿色稻米生产区,采用2001—2003年3月1日后当地有效积温和越冬代水稻二化螟性信息素诱捕器诱蛾数据,用双参数韦布尔函数模型探讨了有效积温和诱捕器诱蛾量之间的关系。结果表明:模型具有很好的拟合性,由韦布尔函数模型y=100×{1-exp[-(x/384.173 9)3.954 3]}确定当地越冬代水稻二化螟发蛾始盛期、高峰期和盛末期所需有效积温分别为247.010,350.172,447.769℃。借助该模型,只要知道当地3月1日后有效积温就可以预测相应日期诱蛾量,可及时指导大田防治。     

Measuring heights to crown base and crown median with LiDAR in a mature,even-aged loblolly pine stand

This study evaluated the possibility of measuring the height to the base of the live crown and the height to the median of canopy elements with airborne scanning LiDAR (Light Detection And Ranging) in a simple, even-aged stand of loblolly pine. The first step in determining these heights was fitting truncated Weibull functions to the vertical distribution of elevations where discrete laser pulses were reflected from the dominant canopy strata. The height to the canopy median was defined as height at the median of the distribution. The height to the base of the live crown was defined as the height where the upper tail the distribution asymptotes to zero returns. Ground-based and LiDAR-based estimates of the canopy median differed by 0.3 m and were not significantly different (P = 0.23). Ground- and LiDAR-based estimates of the base of the live crown differed by 0.6 m and were significantly different (P = 0.03). LiDAR-based estimates of the canopy median exhibited positive bias over most of the range of field-measured values. Analyses of the LiDAR data resulted in overestimating the height to the canopy base over most of the range in field-measured values; however, the difference between ground and LiDAR-based estimates were negatively correlated with ground-based measurements. Average tree diameter was calculated with LiDAR-generated heights to the canopy median and to the base of the live crown. The overall average diameter was not statistically different from the overall quadratic mean diameter measured on the ground, demonstrating the possible utility of these canopy variables to forest managers working with simple stands such as plantations.     

Computer Simulation of Fiber Length and Width Distribution for Two Poplar Woods

1 INTRODUCTIONPoplar is the major afforestation species in China, andhas been used for pulping since 1960s (Xu Weiying,1988). Fiber morphology makes remarkable effectson quality of paper, and attract great attention (KurtH M, Lynch D L, 2001).The quantification, via modeling, of the variation inwood properties is usually accomplished usingstatistical techniques. Fundamental of theseapplications is a variety of probability distributions(Melo, et al, 2000). Due to considerable degree of…     

基于Weibull分布函数的马铃薯丁薄层热风干燥特性

为了实现马铃薯的规模化热风干燥,提高脱水制品的品质、降低生产能耗和成本,该文以薄层干燥试验为基础,研究了鲜切马铃薯丁在不同热风温度（40、50、60、70、80、90℃）、风速（0.5、1.0、1.5、2.5、3.5 m/s）和切丁长度（2.5、5、10、15 mm）条件下的干燥曲线、水分有效扩散系数和干燥活化能。利用Weibull分布函数拟合了干燥曲线,并建立了风温、风速和切丁长度与模型参数的定量关系。研究表明：鲜切马铃薯丁的热风干燥过程服从 Weibull 分布函数（R2=0.991～0.999）,是典型的降速干燥过程,模型的尺度参数与热风温度、风速和切丁长度有关;模型的形状参数与风速和切丁长度有关,而温度对其影响不显著（P＞0.05）;水分有效平均扩散系数在1.859～12.509×10-9 m2/s之间,与热风温度和风速显著相关（P＜0.05）,而物料切丁长度对其影响不显著（P＞0.05）;几何尺寸值与干燥物料的切丁长度和风速有关;马铃薯丁热风干燥的活化能为19.107 kJ/mol。该研究可为马铃薯热风干燥提供理论和技术基础。     

基于Mohr-Coulomb准则的岩石损伤统计分析方法研究

从探讨基于Mohr-Coulomb准则的新的岩石微元强度表示方法及其服从Weibull随机分布的特点出发，基于岩石三轴应力应变试验曲线，建立了反映岩石破裂全过程的损伤软化统计本构模型．在此基础上，重点研究了Weibull分布参数对岩石损伤软化统计本构模型的影响，并结合岩石三轴应力应变试验曲线的特征，对岩石损伤软化统计本构模型进行了合理修正．与试验结果及前人研究结果比较，该模型形式简单，能更好地反映工程实际，具有广阔的应用前景。     

利用Weibull分布函数预测林木的直径分布

1.提出了在解析植物群体的直径分布时不划分直经阶,直接求累计频度的方法;2.提出和讨论了用最小二乘法求解Weibull分布函数的参数的方法,并用此法推算了日本落叶松(Larix leptolepis)模拟密度试验林分的直径分布的各参数;3.weibull分希函数的两种形式(1式和2式)在解析直径分布时,都具有较高的拟合度;4.对平均直径和Weibull分布的各参数之间的关系作了探讨,提出了它们之间的近似表达式。利用这些关系式,可简单地由平均直径预测林分的直径分布。