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基于混合效应的兴安落叶松树高与胸径关系模拟 被引量:10
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作者 李婉婷 姜立春 万道印 《植物研究》 CAS CSCD 北大核心 2014年第3期343-348,共6页
以黑龙江省带岭林业局大青川林场和永翠林场的兴安落叶松人工林为研究对象,基于41块样地调查数据和Richards模型,构建了含有林分变量的树高与胸径关系模型。利用混合效应模型方法拟合常规Richards模型yij=(β1+bi1)(1-e-(β2+bi2)xij)(... 以黑龙江省带岭林业局大青川林场和永翠林场的兴安落叶松人工林为研究对象,基于41块样地调查数据和Richards模型,构建了含有林分变量的树高与胸径关系模型。利用混合效应模型方法拟合常规Richards模型yij=(β1+bi1)(1-e-(β2+bi2)xij)(β3+bi3)+εij和含有林分变量的模型yij=(β1+bi1)(Dq)(β2+bi2)(1-e-(β3+bi3)(N(β4+bi4))xij)+εij。结果表明:当对Richards混合效应模型拟合时,引入随机参数b1、b2时模型拟合最好;当对含有林分变量的Richards混合效应模型拟合时,引入随机参数b2、b4时模型拟合最好。模型检验表明:当随机抽取独立样本时,混合模型误差小于固定效应模型。如果随机抽取4个样本校正时,混合模型的误差和均方根误差降低71.8%和42.1%。 展开更多
关键词 树高-胸径模型 混合效应 样地效应 落叶松
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基于非线性混合模型的栓皮栎树高与胸径关系研究 被引量:41
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作者 李春明 李利学 《北京林业大学学报》 CAS CSCD 北大核心 2009年第4期7-12,共6页
以西北农林科技大学测量的39块栓皮栎样地数据为例,首先选择非线性最小二乘法对6个常用方程进行模拟,找出模拟精度最高的模型作为基础模型。然后,利用基础模型及模拟数据构建非线性混合效应模型,分别考虑区域效应和样地效应,通过变化混... 以西北农林科技大学测量的39块栓皮栎样地数据为例,首先选择非线性最小二乘法对6个常用方程进行模拟,找出模拟精度最高的模型作为基础模型。然后,利用基础模型及模拟数据构建非线性混合效应模型,分别考虑区域效应和样地效应,通过变化混合参数个数并利用SAS软件进行模拟,选择对数似然值、AIC和BIC值最小并且收敛的混合模型作为最优模型。最后利用验证数据与传统的非线性最小二乘法进行精度比较。结果表明:由于h=1.3+[(a1+a2BA+a3ha)exp(b1/D)]+ei考虑了林分断面积和优势木平均高,在模拟单木的树高时精度比其他5个模型高,并且该模型对于描述单木树高的生长趋势效果显著,因此作为构建非线性混合模型的基础模型。利用AIC、BIC和对数似然值来评价非线性混合模型的效果,结果表明:考虑区域效应的影响时,a2、a3、b1同时作为混合参数的模拟效果最好;考虑样地效应的影响时,a1、b1同时作为混合参数的模拟效果最好。无论考虑区域效应影响还是考虑样地效应影响,混合模型的拟合精度都比固定模型的模拟精度高,并且考虑样地效应影响要比考虑区域效应影响的精度更高。 展开更多
关键词 栓皮栎 非线性混合模型 树高-胸径 区域效应 样地效应
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Study on the Edge Effect of Orthopteran Community in Ningxia Helan Mountain
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作者 贺海明 杨贵军 +1 位作者 何立荣 王新谱 《Agricultural Science & Technology》 CAS 2010年第2期113-116,145,共5页
[Objective] The study aimed to discuss the influences of edge effect on orthopteran community in east slope of Helan Mountain.[Method] Samples are collected by using sample zone method.The different species of orthopt... [Objective] The study aimed to discuss the influences of edge effect on orthopteran community in east slope of Helan Mountain.[Method] Samples are collected by using sample zone method.The different species of orthopterans in different habitats are recorded.[Result] The percentage of Oedipodidae,Catantopidae and Pamphgidae in total are 42.65%,29.15% and 12.76% respectively.From scattered grassland interior to edge and then to desert grassland,abundance increase in turn,but diversity in the edge is the highe... 展开更多
关键词 ORTHOPTERA Edge effect Diversity Scattered grassland-desert grassland Ecosystem Helan Mountain
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Drought weakens the positive effect of plant diversity on community biomass
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作者 Yanhui Hou Xiaona Li +7 位作者 Yanxia Hu Xuwei Lu Yue Ma Wenmin Li Xiran Lü Zimo Li Yaxuan Bai Chao Wang 《Journal of Plant Ecology》 SCIE CSCD 2024年第4期141-153,共13页
Drought can greatly impact the biodiversity of an ecosystem and play a crucial role in regulating its functioning.However,the specific mechanisms by which drought mediate the biodiversity effect(BE)on community biomas... Drought can greatly impact the biodiversity of an ecosystem and play a crucial role in regulating its functioning.However,the specific mechanisms by which drought mediate the biodiversity effect(BE)on community biomass in above-and belowground through functional traits remain poorly understood.Here,we conducted a common garden experiment in a greenhouse,which included two plant species richness levels and two water addition levels,to analyze the effects of biodiversity on aboveground biomass(AGB),belowground biomass(BGB)and total biomass(TB),and to quantify the relationship between BEs and functional traits under drought conditions.Our analysis focused on partitioning BEs into above-and belowground complementarity effect(CE)and selection effect(SE)at the species level,which allowed us to better understand the impacts of biodiversity on community biomass and the underlying mechanisms.Our results showed that plant species richness stimulated AGB,BGB and TB through CEs.Drought decreased AGB,BGB and TB,simultaneously.In addition,the aboveground CE was positively associated with the variation in plant height.SEs in above-and belowground were negatively correlated with the community mean plant height and root length,respectively.Furthermore,drought weakened the aboveground CE by decreasing variation in plant height,resulting in a reduction in AGB and TB.Our findings demonstrate that the complementarity of species is an important regulator of community biomass in above-and belowground,the dynamics of biomass under environmental stress are associated with the response of sensitive compartments. 展开更多
关键词 biodiversity effect DROUGHT plant height root length aboveground biomass belowground biomass
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