应用修正指数分布式描述异龄林直径分布的研究

本文介绍了修正指数分布式的简单推导过程和应用过程,阐明了利用修正指数分布式描述异龄林直径分布是可行的。     

对典型异龄林直径分布的研究

通过调查数据分析 ,直径结构径阶愈小 ,株数密度愈大 ,在规模较小的抚育伐后的林分中 ,直径分布保持稳定规律 ,曲线呈反J字型。     

关于异龄直径分布优化的研究

本文介绍了异龄林直径分布优化决策方面的研究概况。     

现实异龄林分最佳直径分布模型的探讨

根据在林业中已应用的直径分布模型的统计特征,选择适宜于异龄林分直径分布模拟的指数分布、韦布尔分布、贝塔分布模拟现实异龄林分直径分布。结果表明,对于现实经营林分,由于直径分布不连续、左偏等原因,韦布尔分布模拟效果最好,贝塔分布次之,指数分布最差,这表明现实林分距理想林分还有较大差距。     

基于林木多期直径测定数据的异龄林年龄估计方法Ⅱ

基于林木多期直径测定数据,拟合直径与年龄相关的生长模型,为异龄林年龄结构的确定提供估计方法。以木荷异龄林为研究对象,通过确定异龄林林分内各树种的年龄变异范围,对林木第一期测量直径取随机年龄,获取林分内所有林木的直径与年龄信息对,进而利用Richards方程拟合各树种的直径生长方程,最后将加权平均直径代入生长方程求算出各树种及林分的平均年龄。结果表明:1)木荷异龄林林分内木荷树种的年龄变异范围为[-7.46*ln(1-(D/20.06)^0.371),-17.24*ln(1-(D/26.78)^0.381)],马尾松的年龄变异范围为:[-8.55*ln(1-(D/15.32)^0.478),-6.41*ln(1-(D/10.01)^0.326)],杉木的年龄变异范围为:[-10.75*ln(1-(D/21.04)^0.587),-10.53*ln(1-(D/12.20)^0.576)]。2)木荷估计年龄与真实年龄的最大绝对误差≤3年,最大绝对相对误差<20%,平均绝对百分误差<11%;马尾松估计年龄与真实年龄的最大绝对误差≤1年,最大绝对相对误差<10%,平均绝对百分误差≤5%;杉木估计年龄与真实年龄的最大绝对误差≤3年,最大绝对相对误差≤15%,平均绝对百分误差<10%;林分估计年龄与真实年龄的最大绝对误差均≤3年,最大绝对相对误差均<20%,平均绝对百分误差均<11%,预测效果较好,其估计方法可以应用于科研和生产实践。     

异龄林经营决策优化

从林分密度、树种组成、林分直径分布、转换决策 (包括择伐周期与转换期长度 )等方面对异龄林经营决策优化进行了研究。     

国外异龄林经营管理研究综述

以社会林业──森林经营方式──异龄林经营管理理论和方法、结合定量化分析方法和决策技术的进步为线索，综述了国外异龄林经营方式变迁、择伐林作业效益评价、异龄林立地质量评价和林型分类、异龄林生长收获及择伐等方面的研究。     

利用微机绘制森林病虫害发生分布图

利用微机把森林病虫害发生的分布区域、病虫害种类，灾情等级等信息自动绘制成图，为防虫设计提供依据，详细介绍了该软件的实现方法和操作过程。     

林分模拟径阶株数法确定小班蓄积的试验

利用数学模拟方法对小班林木径阶株数分布和小班蓄积量进行了模拟试验，结果表明：模拟法与标准地实测法差异不显著，且模拟法具有实用性强、生产使用方便、能充分发挥计算机的优越性等特点，可以快速模拟出林分的直径分布，为林业调查提供了快捷有效的技术手段。     

金沟岭林场云冷杉次生林两种径阶分布模型的应用

在现代森林经营管理过程中,掌握某树种径阶的分布状态是进行经营管理决策的重要依据。目前使用较多的是Weibull函数,它具有较大的灵活性,能够拟合单峰山状曲线及反J型曲线,并且拟合林分直径的效果比较好。但是weibull分布函数有一定的适用范围,应用于次生林的时候,拟合效果并不好。     

冀北山区不同森林类型林木胸径Weibull分布规律研究

林木胸径是林分结构的基本特征,在林分生长过程中,胸径分布遵循一定的变化规律。该文利用Weibull分布密度函数对冀北山区几种典型林分类型林木胸径分布规律进行拟合。结果表明:落叶松桦树混交林的胸径分布预测值曲线拟合度不高,山杨白桦混交林预测值曲线拟合度非常高,为具有正偏的曲线图。油松蒙古栎混交林预测值曲线拟合度较低,具有明显的偏峰,但是对于胸径在15cm以上的树种拟合度较好。     

Modelling the diameter distribution of Pinus sylvestris, Pinus nigra and Pinus halepensis forest stands in Catalonia using the truncated Weibull function

Parameter prediction models for the diameter distribution ofPinus sylvestris L., Pinus nigra Arn. and Pinus halepensis Mill.in Catalonia were developed using the truncated Weibull functionas the theoretical distribution. The parameter models allowone to use individual-tree models in the simulation of standdevelopment when only stand-level data are collected in forestinventories. Parameter models for the diameter distributionof stand basal area were developed. The data consisted of permanentsample plots from the Spanish National Forest Inventory in Catalonia.A total of 1780 empirical distributions of P. sylvestris, 1204distributions of P. nigra and 1535 distributions of P. halepensiswere used as modelling data. The empirical data represent left-truncateddistributions, as the smallest diameter measured in the fieldwas 7.5 cm. Two different approaches, namely, regression (two-stepmethod) and optimization approach (one-step method), were usedto find the coefficients of the parameter models. In the two-stepmodelling method, the Weibull parameters were first estimatedseparately for every empirical distribution by maximizing thelog-likelihood function of the Weibull density function. Inthe second-step, regression analysis was used to find the relationshipbetween Weibull parameters and stand basal area, number of treesper hectare and elevation of the site. The one-step method usedoptimization to find such coefficients for the parameter models,which minimized the mean of the squared differences betweenempirical and predicted cumulative tree frequencies in the wholemodelling data. The one-step optimization method performed betterthan the two-step regression method for all tree species. Theparameter prediction models developed in this study enable theprediction of the diameter distribution of P. sylvestris, P.nigra and P. halepensis in Catalonia from limited stand information.     

用计算机模拟闽粤栲天然林生长模型

通过建立单木生长模型、林木枯死模型和林分生长模型来模拟闽粤栲天然林生长规律,结果表明:用这3个模型对所调查样地内林木蓄积进行预测,作为林木蓄积量理论计算值,以二元材积表查表得到的蓄积量作为林木蓄积量的实际值,其精度可达94.15%。这些模型对于模拟闽粤栲天然林的生长规律具有一定的应用价值。     

Modeling diameter distributions of mixed-species forest stands

This study compares three diameter distribution models to fit mixed-species forest stands using four example plots with two or three species components in Daxing'an Mountain, PR China. The methods include (1) a finite mixture model (FMM) to fit two or three species components simultaneously, (2) a single Weibull function to fit the whole plot only, and (3) a single Weibull function to fit each species component separately and the summation of the individual species produced the whole plot. Our results indicated that Method 2 is only suitable to regular and unimodal diameter distributions with a balanced reversed J-shape. Method 3 may be able to fit each species component well if its frequency distribution is known and available in the data. However, Method 3 ignores the interspecies relationships within a given plot. Thus, the summation of the species components may not produce a good fit for the whole plot. In contrast, Method 1 (FMM) fits the species component distributions simultaneously with the constraint that the individual components add up to the whole plot, without requiring the observed frequencies for each species across the diameter classes. The FMM models are more flexible to describe highly skewed and irregular diameter distributions for the whole plot, as well as provide the acceptable estimation for each species component and the mixing proportions. Thus, the FMM models can be a useful tool for effectively managing mixed-species forest stands.     

非参数核密度估计在岷江冷杉天然林直径分布研究中的应用

在介绍非参数核密度估计方法的基础上，对天然岷江冷杉林直径结构进行了拟合，结论是：非参数核密度估计能对天然林直径进行了很好的拟合，且方法简单灵活、可靠性强。     

Modelling joint distribution of tree diameter and height using Frank and Plackett copulas

Bivariate distribution models are veritable tools for improving forest stand volume estimations. Their accuracy depends on the method of construction. To-date,most bivariate distributions in forestry have been constructed either with normal or Plackett copulas. In this study, the accuracy of the Frank copula for constructing bivariate distributions was assessed. The effectiveness of Frank and Plackett copulas were evaluated on seven distribution models using data from temperate and tropical forests. The bivariate distributions include: Burr III, Burr XII, Logit-Logistic, Log-Logistic, generalized Weibull,Weibull and Kumaraswamy. Maximum likelihood was used to fit the models to the joint distribution of diameter and height data of Pinus pinaster(184 plots), Pinus radiata(96 plots), Eucalyptus camaldulensis(85 plots) and Gmelina arborea(60 plots). Models were evaluated based on negative log-likelihood(-■). The result show that Frank-based models were more suitable in describing the joint distribution of diameter and height than most of their Plackett-based counterparts. The bivariate Burr III distributions had the overall best performance. The Frank copula is therefore recommended for the construction of more useful bivariate distributions in forestry.