Site Quality Evaluation And Growth Regularity Of E.urophylla × E.tereticornis Pulpwood Plantation In Hainan Island And Leizhou Peninsula Region

E.urophylla×E.tereticornis is one of the important pulpwood species in south China,which has been widely planted because of its fast-growing and good stress resistance.With the demand of raw materials for the development of pulp industry,it has become an inevitable choice to build high-quality and high-yield Eucalyptus pulp plantation.E.urophylla×E.tereticornis is the first choice for eucalyptus afforestation in typhoon prone region of Hainan island and Leizhou peninsula（hereinafter referred to as"Leiqiong region"）.In the process of plantation cultivation,due to the lack of scientific cultivation division,the relationship between forest growth and site productivity is still shallow,and the phenomenon of soil fertility decline and productivity reduction appears,which restricts the sustainable management of E.urophylla×E.tereticornis plantation.In this study,the large-area planted E.urophylla×E.tereticornis plantation in Leiqiong region was taken as the research object.Through the investigation and sampling of temporary standard plot,the data information of tree growth,site factors（vegetation,soil,topography,etc.）and stem-analysis were obtained.The correlation between the growth and site factors of E.urophylla×E.tereticornis plantation was analyzed,the site type division and quality evaluation of E.urophylla×E.tereticornis plantation were carried out,and the growth regularity and pulping and papermaking performance of the forest were discussed,so as to give full play to the productive potential of the site and provide theoretical basis and guidance for the scientific management of E.urophylla×E.tereticornis pulp forest in Leiqiong region.The main results are as follows:（1）The undergrowth plants of E.urophylla×E.tereticornis plantation in Leiqiong region were relatively rich.There are 63 species,59 genera and 30 families in Leizhou area.The main herbaceous plants are Chromolaene odorata,Bidenspilosa L.,Borreria latifolia,Praxelis clematidea,Imperata cylindrica,Panicum bisulcatum Thunb.,Mikaniamicrantha Kunth and Dactyloctenium.The main shrub plants are Clerodendrum cyrtophyllum,Aporosa dioica,Urena procumbens Linn,Dodonaea viscosa,Mallotus paniculatus and Embelialaeta（L.）Mez.There are 234 species belonging to 196 genera of 82 families in Hainan.The dominant species of herbs mainly include Chromolaene odorata,Borreria latifolia,Ageratum conyzoides,Conyza canadensis,Herba Hedyotidis Anriculariae,Lygodium japonicum.,Eleusine indica,Setaria viridis,Digitaria sanguinalis,Mimosa pudica,Miscanthus sinensis,etc.The dominant species of shrub mainly include Urena lobata,Mallotus apelta,Clerodendrum cyrtophyllum,Melastoma candidum,Dodonaea viscosa,Lantana camara,Aporosa dioica,Zanthoxylum avicennae,etc.The results showed that the difference of age group and site had significant effects on plant richness and diversity（P<0.05）.The competitive relationship between forest growth and herbaceous plants was obvious.Soil physical and chemical properties and environmental factors were closely related to forest and plant diversity.Soil bulk density,soil organic matter,phosphorus and potassium content were important influencing factors of plant diversity and plantation growth,and trees and vegetation play an important role in maintaining forest quality and soil nutrient cycling.According to the analysis of soil nutrient classification standard,the soil of E.urophylla×E.tereticornis plantation in Leiqiong region is mainly acidic,the content of organic matter is medium and low,the content of nitrogen is low,and the content of phosphorus and potassium is relatively poor.The principal component and k-means cluster analysis of soil nutrient show that 87.5%of the soil nutrient content in Leiqiong region is in the middle or lower level,which indicates that the soil nutrient in Leiqiong region is poor on the whole.In the management of plantation,the tending management of fertilization should be strengthened,especially the supplement of phosphorus and potassium.（2）According to the selected seven site factors,combined with the classification table,the site factor data（0,1）were transformed into independent variables,and the annual average growth of dominant tree height in the sample plot was taken as dependent variable.The regression model Y=1.907-0.659X₁₂-0.685X₁₃+0.407X₂₁+0.16X₂₂+0.031X₂₃-0.136X₃₁-0.244X₃₃-0.384X₄₁-0.183X₄₃+0.123X₄₄-0.559X₅₁-0.091X₅₃+0.569X₆₁-1.339X₆₃+0.264X₇₂+0.752X₇₃was established by using quantitative theory I method.According to the combination of simple,practical and dominant factors,the site types of E.urophylla×E.tereticornis plantation in Leiqiong region were classified into 12 site types by selecting three site factors,namely soil texture,soil parent rock and soil bulk density.According to the predicted potential score,the site types were divided into four productivity grade groups:grade I（2.8-3.2m）,grade II（2.4-2.8m）,grade III（1.8-2.4m）and grade IV（1.4-1.8m）.And it is concluded that E.urophylla×E.tereticornis grew best and the productivity was the highest when it was planted in loam soil with shallow sea sediment and basalt and low and medium soil density.（3）By using the method of quantitative theory I,taking the annual average growth of dominant tree height as the dependent variable and each site factor as the independent variable,the quantitative regression fitting was carried out,and the minimum contribution factor was removed in turn.The quantitative site quality score table and productivity evaluation table were compiled.The applicability test showed that the evaluation table was reliable.When the site factors were used to predict the site quality in Leiqiong region,the grade ranges were 2.49-3.15（excellent）,1.83-2.49（good）,1.17-1.83（medium）and<1.17（poor）.Most of the E.urophylla×E.tereticornis plantation sites in Leiqiong region are above the middle level,indicating that the afforestation layout is basically reasonable.Based on the dominant high age data obtained from the sample plot survey,the models of Richard,Kolf,Logistic,Campetz and so on were used to fit the data,the Korf equation H=38.668*e^{（-1.725/A^0.470）}was selected as the traverse curve equation for compiling site index table.The coefficient of variation of dominant height tends to be stable after 5 years,so the base year of E.urophylla×E.tereticornis plantation was 5 years,and the index interval was 2 m.Seven grade site index tables of 12 m,14 m,16 m,18 m,20 m,22 m and 24 m were compiled by standard deviation adjustment method.Through significance and falling point test,this table has a good application effect in site quality evaluation of artificial forest in Leiqiong region,and can provide guidance for production practice.（4）Based on the stem analysis data of dominant trees in various areas,through the growth fitting of nine alternative theoretical models and empirical models,it showed that Power and Logarithm models had higher fitting degree for tree height growth,Powe,Logarithm and Quadric models were more suitable for DBH growth fitting,and Gompertz model was the best for volume growth.The best growth model expressions for height,DBH and volume of E.urophylla×E.tereticornis with different site productivity grades were obtained.The growth process of a 15-year-old E.urophylla×E.tereticornis was fitted useing the best model to analyze the growth regularity of the tree,it can be seen that the growth of E.urophylla×E.tereticornis varied greatly with different site productivity levels.Combined with the variation regularity of volume growth,the quantitative maturity ages of grade I,grade II,grade III and grade IV were determined,which were 8.5a,7.5a,6.5a and 5.5a respectively.The site quality was more higher,the quantitative maturity age was more longer,which was basically consistent with the rotation period of 5-7a in actual production.（5）According to the analysis of wood properties,chemical components and pulping performance of E.urophylla×E.tereticornis with different site quality,the grade I had great advantages in pulp yield and pulping process difficulty,which was more suitable for cultivating E.urophylla×E.tereticornis pulpwood.The analysis of wood properties,chemical composition and pulping characteristics of E.urophylla×E.tereticornis at different ages showed that the basic density,fiber length,fiber width and fiber length width ratio of E.urophylla×E.tereticornis increased with the increase of age.The chemical composition and pulp yield were slightly different,but the change was not significant.Comprehensive analysis shows that the technology mature age of E.urophylla×E.tereticornis plantation in Leiqiong region was 5-7years.