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site index for Chinese fir plantations varies with climatic and soil factors in southern China

Journal of Forestry Research 2022年第6期33卷 1765-1780页

作者： Xiaoyan Li Aiguo Duan Jianguo Zhang State Key Laboratory of Tree Genetics and Breeding Key Laboratory of Tree Breeding and Cultivation of National Forestry and Grassland AdministrationResearch Institute of ForestryChinese Academy of ForestryBeijing 100091People’s Republic of China Collaborative Innovation Center of Sustainable Forestry in Southern China Nanjing Forestry UniversityNanjing 210037People’s Republic of China

Chinese fir[Cunninghamia lanceolata(Lamb.)Hook.]has a large native distribution range in southern ***,we tested differences in productivity of Chinese fir plantations in different climatic regions and screened the main environmental factors affecting site productivity in each *** of a Chinese fir site index with climatic factors and the soil physiochemical properties of five soil layers were examined in a long-term positioning observation trial comprising a total of 45 permanent plots in Fujian(eastern region in the middle subtropics),Guangxi(south subtropics)and Sichuan(central region in the middle subtropics)in southern *** mixed effects models were developed to predict the site index for Chinese fir,which was found to vary significantly among different climatic *** P,total N,bulk density and total K were dominant predictors of site index in three climatic *** regional linear mixed models built using these predictors in the three climatic regions fit well(R~2=0.86–0.97).For the whole study area,the available P in the 0–20-cm soil layer and total N in the 80–100-cm soil layer were the most indicative soil *** was the most important climatic variable influencing the site *** model evaluation results showed that the fitting performance and prediction accuracy of the global site index model using the climatic region as the dummy variable and random parameters and the most important soil factors of the three climatic regions as predictors was higher than that of global site index model using the climatic variable and the most indicative soil variables of the whole study *** results will help with further evaluation of site quality of Chinese fir plantations and the selection of its appropriate sites in southern China as the climatic changes.

关键词： site productivity site index Climate Soil Chinese fir

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Stochastic frontiers or regression quantiles for estimating the self-thinning surface in higher dimensions?

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Journal of Forestry Research 2021年第4期32卷 1515-1533页

作者： Dechao Tian Huiquan Bi Xingji Jin Fengri Li Key Laboratory of Sustainable Forest Ecosystem Management-Ministry of Education School of ForestryNortheast Forestry UniversityNo.26 Hexing RoadHarbin 150040People’s Republic of China Forest Science NSW Department of Primary Industries−ForestryLevel 1210 Valentine AveParramattaNSW 2150Australia School of Ecosystem and Forest Sciences The University of MelbourneParkvilleVIC 3010Australia

Stochastic frontier analysis and quantile regression are the two econometric approaches that have been commonly adopted in the determination of the self-thinning boundary line or surface in two and higher dimensions since their introduction to the field some 20 years ***,the rational for using one method over the other has,in most cases,not been clearly explained perhaps due to a lack of adequate appreciation of differences between the two approaches for delineating the self-thinning *** an adequate understanding of such differences,the most informative analysis may become a missed opportunity,leading to an inefficient use of data,weak statistical inferences and a failure to gain greater insight into the dynamics of plant populations and forest stands that would otherwise be *** data from 170 plot measurements in even-aged Larix olgensis(***) plantations across a wide range of site qualities and with different abundances of woody weeds,*** regenerated non-crop species,in northeast China,this study compared the two methods in determining the self-thinning surface across eight sample sizes from 30 to 170 with an even interval of 20 observations and also over a range of quantiles through repeated random sampling and *** all sample sizes and over the quantile range of 0.90 ≤τ≤0.99,the normal-half normal stochastic frontier estimation proved to be superior to quantile regression in statistical *** parameter estimates had lower degrees of variability and correspondingly narrower confidence *** greater efficiency would naturally be conducive to making statistical *** estimated self-thinning surface using all 170 observations enveloped about 96.5% of the data points,a degree of envelopment equivalent to a regression quantile estimation with aτ of *** stochastic frontier estimation was also more objective because it did not involve the subjective selection of a particular value

关键词： Larix olgensis Normal-half normal distribution site productivity Woody weeds Sample size Quantile selection

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