| Betula alnoides is a fast-growing valuable indigenous timber species with multiple usesin the tropical and warm subtropical regions in China.In recent one and a half decades,it has been widely planted,and its area is over 150,000 hm2 by 2014.However,some problems such as poor stand growth and low productivity have been occurring due to mismatching the species with sites under lack of systematic study onsite type classification and site quality evaluation of B.alnoidesplantions in the process of rapid development of this species.Growth of plantations from young to mature stage in Daqingshan forest area,Guangxi and the young and middle-aged plantations in Yunnan main cultivation areas(YMCA),were investigated as well as information of site factors were obtained in terms of topography and soil properties etc.by large-scale plot surveysin the present study to estimate growthof B.alnoides plantations through developing height-diameter models,taper functions andbark thickness models;to examine effects of all sorts of site factors on B.alnoides growth by application of Quantitative Theory I;to carry out further site type classification for main planting areas of B.alnoides;and to evaluate site quality usingthe methods including guide curve,difference equation(Polymorphic site index curves)and quantitative site score table.The findings will not only be contributed to reasonable management of the present plantations,but also provide scientific and technical support for large-scale spread of B.alnoides in the future.The main results of the present study were as follows:(1)The best fit models of dominant height-diameter,taper and bark thickness were selected for B.alnoides plantations,respectively.Eleven height-diameter equations were applied to fit the data sets of dominant or codominant trees in 206 sampling plots in Guangxiand Yunnan,and 28 taper functions and 13 bark thickness models were used to fit the data sets from stem analysis of dominant treesin part of these sampling plots.A serial of models with good fitness were screened out after model fitting,parameters' significance test and residual analysis,etc.Equations of (?) were suitable for predicting dominant height based on DBH of dominant trees.Muhairwe(1999)model,a kind of variable-form,(?),was the best to predict the diameter at any height on the stem.(?) and dib=-0.147+0.933 dob were selected to estimate bark thickness at breast height,bark thickness at any height,relative bark thickness and diameter inside bark at any height,respectively.(2)B.alnoides plantationsarehighly adaptable to the acid,low potassium,phosphorus deficiency and poor soil.Ten items of soil chemical properties were measured in ECTF and YMCA,classification of each item was assessed according to soil nutrient classification standard published,soil fertility index of each plot was then calculated by principal component analysis,and soil fertilities of B.alnoides plantations in ECTF and YMCA were evaluated by clustering analysis method.The results showed that the soils in ECTF were strongly acidic with upper-middle level of soil organic matter(SOM)and total nitrogen(TN)contents,and lower-middle level of other items,their soil fertility were at lower-middle level;and the forest soils in YMCA were acidic and were characterized by upper level of SOM and TN and lower level of total phosphorus and effective phosphorus contents,and their soil fertility were of middle level.Overall,the soil fertility in B.alnoides plantations was of middle-to-lower level with high acidity and lack of phosphorus.(3)The key factors affectingB.alnoides plantation growth were selected,and site typesof B.alnoides plantationswere classified.The data sets of soil physical and chemical properties and topographical factors were transformed into(0,1)matrix based on grading of each factor;Quantitative Theory I was then applied to explore the relationship between B.alnoides growth and site factors using site index and mean annual increment of dominant height as dependent variable at ECTF and YMCA,respectively;dominant site factors influencing B.alnoides growth were screened out;and site types were further classified using these dominant factors according to the principle of easy application in practice.The results indicated that B.alnoides plantations in ECTF could be divided into 16 site types using three dominant factors including altitude,slope aspect and slope position,and the plantations on shady,semi-shady slope at high altitude is of high productivity;and thirty-one site types were determined by three dominant factors such as slope aspect,slope position and slope degree,and plantations on shady and half shady-downhill-gentle slope were of high productivity in YMCA.As a whole,topographical factors should be considered first when planting B.alnoides,and shady or half-shady slopesare mostly suitable for planting.(4)Site index table of B.alnoides plantation in ECTF was compiled.9 models were selected to model data setsof stem analysis of dominant trees,which including the generalized single molecular formula,Logistic,Korf,Richards,and so on.Among nine models fitted,Richards equation,(?),performed the best with large R~2 and small AMR and RMSE,and was selected as guide curve.The reference age was determined as 15 years since current growth increment and variation coefficient of dominant height tended stable,and interval of site index class as two meter taking fast growth and range of dominant tree height(15.2-25.8m)into consideration.The site index table was thus developed.It was indicated from test that no significant difference existed between site index table and growth process of dominant tree height,and estimation error analysis at aspects of site index and stand age showed that the table had high forcast accuracy.The site index table could be used for site quality evaluation of B.alnoides plantations in ECTF and regions with similar site conditions.(5)Difference equationswere used to fitdata sets of high-age and develop polymorphic index curves.Five theoretical equations(Richards,Weibull,Korf,Logistic and Schumacher)and eight difference equations transformed from above 5 theoretical models were fitted separately height-age and two height-two age data sets obtained from stem analysis of dominant trees in ECTF and Dehong,Yunnan.The best equations were selected based on comparison of fitting statistics,residual analysis and biological explanation,and polymorphic site index equations were then built.It was indicated that Logistic model was not suitable for modeling relationship between dominant height and age,difference equations had better accuracy than theoretical equations,three-parameter difference equations from Richards and Weibull models performed better than their two-parameter forms.Taking fitting statistics,residual analysis and biological explanation into consideration,Korf difference equation was suitable to develop polymorphic site index equations for B.alnoides plantations,the model was(?)(6)Quantitative site quality score tablesand evaluation tables were established.Aseri es of quantitative predicting equations and site quality score table were obtained by usi ng Quantitative TheoryImethods modeling site index or mean annual increment of domi nant height with site factors and judging factor contribution according to partial correlat ion and scoring range of each site factor,quantitative site quality evaluation tables wer e then established to evaluate site productivity ofnon-forest land with similar climate at ECTF and YMCA.The results showed that the scope of site quality grades and site i ndex value estimated with all site factors in EFTC were: excellent,34.6m to 26.1m;go od,26.1m to 17.5m;middle,17.5m to 9.0m,poor,less than 9.0m.In YMCA,the scop e of site quality grades and mean annual increment of dominant height estimated with all site factors were: excellent,2.24 m to 1.76m;good,1.76 m to 1.29m;middle,1.29 m to 0.81 m,poor,less than 0.81 m. |
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