Predicting regeneration establishment in Norway spruce plantations using a multivariate multilevel model

This study predicts the regeneration establishment on 3-year-old Norway spruce (Picea abies (L.) Karst.) plantations in southern Finland using regeneration survey data. Regeneration establishment was described by seven response variables: number of planted spruces, natural Scots pines (Pinus sylvestris L.), natural spruces, natural seed-origin birches (Betula pubescens Ehrh. and B. pendula Roth.) and other broadleaves (i.e. sprout-origin birches and other broadleaves than birch), as well as height of crop-tree spruce and dominant height of broadleaves. Due to the multivariate (several responses for each plot) and multilevel (plot, stand, municipality, forest centre) structure, regeneration establishment was modelled by fitting a multivariate multilevel model with explanatory variables such as temperature sum, site fertility, soil quality and method of site preparation. In the model, the numbers of tree seedlings were modelled using over-dispersed Poisson distributed equations, and the tree heights were modelled using normally distributed linear equations. The estimated fixed and random parameters of the equations were logical, and there was no serious bias in predicting the regeneration establishment in the independent test data set. This modelling approach can be used to predict the regeneration establishment stochastically by taking into account the large unexplained variation in regeneration models.     

随机状态下林分密度调查精度分析

从林木随机分布的角度对林分密度的调查精度进行了相关分析.分析指出,在天然的林分中,林木分布具有一定的随机性,在一定面积的样地中,林木株数服从泊松分布,并得出结论,林分密度调查精度的直接影响因子为调查的林木株数.     

白河林业局红松分布数量预估模型1）

根据长白山地区白河林业局的772块固定标准地调查数据,以及最小二乘法（ OLS）,建立逻辑斯蒂（Logistic）模型来预估该局现时状态有林地的红松分布概率,并采用泊松（Poisson）和负二项分布（Negative binomi-al,NB）模型预估该局现时状态有林地红松的分布数量,并对模型进行了拟合效果评价及独立性检验。结果表明, Logistic模型与数据的拟合效果很好,独立性检验中预测精度也在可接受的范围内,可以利用Logistic模型来预估该局有林地红松的分布概率。与Poisson模型相比,负二项分布模型能够解决因变量的不均匀分布（即过度散布）的问题,因此能够更好地拟合数据。但在独立性检验中,Poisson模型和NB模型的预测精度接近,且都在可接受的范围内,两个模型均可以用来预估该局有林地红松的分布数量。     

高粱苗期病害分布型研究初报

高粱苗期病害主要是由立枯丝核菌(Rhizoctonia solani)AG—5引起的土壤传染病害,该病害的病原菌土下分布状况可以通过病株、病斑的分布型间接地测定。病株为随机分布,而病斑则属于核心分布,但也符合负二项分布.病株分布型反映土内病菌的随机存在,病斑分布型则主要反映了病菌在土内接种势能的不均一分布(聚集分布)。以上结果为在病害调查中确定取样方式与样本大小提供了理论基础。     

关于二项分布的泊松近似计算问题

当n充分大,nP很小时,二项分布近似于参数为λ=nP的泊松分布,计算结果表明,在X区间[0,nP 2σ]内,泊松拟合值才能近似代替二项分布数据。本文利用最小二乘多项式拟合方法求得在不同参数n和P下的泊松近似修正系数,修正后的泊松拟合值与二项分布数据有很好的近似。     

黄土侧向变形的真三轴试验研究

保持小主应力、中主应力不变,在大主应力方向加荷是实际工程中存在的一种应力路径,就该应力路径分别对不同含水率的重塑黄土进行了几组真三轴试验,对其应力-应变关系及反映侧向变形变化规律的泊松比进行了特定条件下的研究.研究结果表明,应力-应变关系的偏差应力和初始切线模量随含水率的增大而减小,相同的偏差应力下含水率越大侧向应变就越大.在上述应力路径下剪切,中主应力方向首先压缩,但表现不明显,很快就转为膨胀,小主应力方向膨胀,泊松比可以大于0.5,且小主应力方向膨胀量大于中主应力膨胀量.     

长白落叶松林分进界模型的研究

利用吉林省汪清林业局金沟岭林场落叶松林分连续观测数据,以计数类模型为基础,分别利用Poisson回归模型、负二项模型、零膨胀模型和Hurdle模型拟合林木进界株数,并通过AIC值,Pearson残差图以及Vuong检验对这些模型进行了详细分析比较.结果表明:Poisson回归模型不适用于模拟林木枯损株数;负二项回归模型相对于Poisson回归模型比较适用,但是对于零枯损过多的数据,这两类模型拟合效果较差;零膨胀模型和Hurdle模型对这类数据有很好的解决办法,而且,零膨胀负二项模型拟合效果最好.     

Slope correction for LAI estimation from gap fraction measurements

Digital hemispherical photography poses specific problems when deriving leaf area index (LAI) over sloping terrain. This study proposes a method to correct from the slope effect. It is based on simple geometrical considerations to account for the path length variation within the canopy for cameras pointing vertically. Simulations over sloping terrain show that gap fraction increases up-slope while decreasing down-slope. As a consequence of this balance between up- and down-slope effects, effective LAI estimates derived from inversion of the Poisson model are marginally affected for low to medium slopes (<25°) and LAI (LAI < 2). However, for larger slopes and LAI values, estimated LAI values may be strongly underestimated. The proposed correction was evaluated over four forested sites located over sloping terrain. Results indicate that in these conditions (LAI between 0.6 up to 3.0, clumped canopies with relatively erectophile leaf distribution), the effect of the slope (between 25° and 36°) was moderate as compared to other potential sources of problems when deriving LAI from gap fraction measurements, including clumping, leaf angle inclination and spatial sampling.     

气候变化适应及其影响因素研究——山东胶州湾地区居民的实证分析

为探索气候变化感知在适应决策过程中的作用机理，本研究以深度访谈数据为基础，基于“感知－适应”分析框架，采用二元Probit模型和泊松回归模型，分析胶州湾地区居民气候变化适应决策和适应选择的影响因素。研究表明，胶州湾地区绝大多数居民已经感知到气候变化，半数以上居民采取了一定的适应措施，大多数居民对适应措施效果的感到满意。居民采取适应措施介于0-4项，平均为1.07项，适应措施的普及率和多样化仍有提升空间。影响胶州湾地区居民气候变化适应决策与适应选择的主要因素存在一定差异性，但“居民对气候变化的感知”不论是对适应决策还是对适应选择的影响都较大，其中又以“对降水变化的感知”和“对气象灾害损失的感知”最为显著。     

经济代理人的最优损失控制

根据经济代理人对风险的厌恶程度高低将影响收益效用的事实,通过对经济代理人的风险厌恶系数引进阈值,使风险厌恶系数在不同取值区间对应不同的效用函数,对经济代理人具有常值绝对风险厌恶的效用函数,损失服从泊松分布、且保险市场被垄断的承保人控制的最优防损活动进行了研究.研究表明,风险厌恶系数、损失的大小以及防损效率将影响最优防损水平.