| Eucalyptus urophylla×Eucalyptus grandis is a fast-growing tree species belonging to the Myrtaceae family and Eucalyptus genus.It is widely cultivated in the world and was an important industrial timber tree and excellent papermaking raw material,with good social,economic and ecological benefits.At present,the domestic lack of understanding of the relationship between eucalyptus growth and site productivity,lack of scientific planning and reasonable site type division and quality evaluation.In the process of expanding the cultivation area,there are problems such as species-site mismatches,low forest productivity and degradation of soil fertility.Based on the distribution and location of E.urophylla×E.grandis pulpwood plantation in southern Yunnan and the key problems restricting its productivity improvement,this study focused on the influence of pulp yield,yield and quality.The site types of E.urophylla×E.grandis pulpwood plantation in this cultivation area were systematically divided by geological and landform,site conditions,soil and other factors.The site quality evaluation and stand growth rules of E.urophylla×E.grandis pulpwood plantation were carried out,which revealed the growth and development process of E.urophylla×E.grandis pulpwood plantation in southern Yunnan,analyzed the structure of the forest and its understory biodiversity,and divided the age of the forest.The forest age group was divided and the site index table of E.urophylla×E.grandis pulpwood plantation in southern Yunnan was compiled.Based on the combination of wood properties and pulping performance indicators,the relationship between the yield and quality of E.urophylla×E.grandis pulpwood plantation was explored,and the cutting age of E.urophylla×E.grandis pulpwood plantation was determined based on the mature age of the volume and the quantitative mature age of the pulping process.This research provided scientific and theoretical basis for the directional cultivation and sustainable management of E.urophylla×E.grandis pulpwood plantation in southern Yunnan.The main conclusions are as follows:（1）The base age of E.urophylla×E.grandis pulpwood plantation in southern Yunnan was6 years,and the forest was divided into 13 categories according to slope position,altitude and soil thickness as the dominant factors.It was divided into 3 class sites with a distance of 4 m,which were class I（24-28 m）,class II（20-24 m）,and class III（16-20 m）.Class I site was mainly located in the lower slope,with an altitude of 900～1200 m and a soil thickness greater than 80 cm.The height,DBH and mean annual growth of E.urophylla×E.grandis were 24.8m,14.9 cm and 38.47 m3·hm-2a-1,respectively.ClassⅡsite was mainly located in the middle slope,with an altitude of 1000～1800 m,and soil thickness of 40～80 cm.The height,DBH and mean annual growth of E.urophylla×E.grandis were 22.2 m,13.8 cm and 27.34 m3·hm-2a-1,respectively.ClassⅢsite was mainly located in the upper slope and flat ground,with an altitude of 1000～1600 m and soil thickness less than 40 cm.The height,DBH and mean annual growth of E.urophylla×E.grandis were 18.3 m,12.3 cm and 15.67 m3·hm-2a-1,respectively.The growth of E.urophylla×E.grandis pulpwood plantation was significantly positively correlated with the content of soil total nitrogen,available phosphorus,available boron,available zinc,organic matter,available copper,total potassium,hydrolytic nitrogen and total phosphorus,and the content of total nitrogen had the greatest effect on the growth of E.urophylla×E.grandis,with an explanative proportion of 18.1%.The content of total potassium,available potassium,organic matter,available zinc,and available copper of classⅠand II site was medium,and the content of total phosphorus and available phosphorus was low.The content of total nitrogen,total phosphorus,available phosphorus and available boron of class II site was low.The content of total nitrogen,total phosphorus,total potassium,available phosphorus,available potassium,organic matter,available boron,available zinc,available copper content of classⅠand II site was low.Therefore,it was necessary to appropriately increase the application of nitrogen,phosphorus,potassium,and boron fertilizers to promote the growth and development of forest in classⅡandⅢsite.Logging operations should retain the forest land with dead branches,fallen leaves and logging residues in order to increase soil organic matter and recycle nutrients in the later period.（2）Based on the survey data of 145 sample plots from 1 to 15 years old and the analytical data of dominant trees,the six equation expressions of the dominant height of E.urophylla×E.grandis was compared,and the Richards equation with the largest R2 and the smallest AMR and RMSE was selected as the optimal guide curve,the expression was:H=35.887*（1-exp（-0.104*t））0.625.The compiled position index table satisfies accuracy test,applicability test,drop point test and tree height growth test.According to the index level of the tree height variation range of E.urophylla×E.grandis pulpwood plantation at the base age of 6years,it was divided into 16,18,20,22,24,26,28 m.The dummy variable growth model of E.urophylla×E.grandis plantation:H=（34.76*S1+31.67*S2+36.25*S3+34.25*S4+33.82*S5+31.72*S6+35.48*S7+37.31*S8+36.61*S9+35.52*S10+36.63*S11+30.66*S12+34.02*S13）*（1-exp（-0.13*t））0.73.The overall fitting degree of dummy variables was better than that of the simplex site index model.At the same time,the difference of residual value between the site index model of different sites and the site index model of similar sites of different ages was relatively small.Therefore,the growth could be estimated by the site index of similar sites of different ages,which could replace the production of analysis wood.（3）E.urophylla×E.grandis was found in young forest（1～3 year）,middle aged forest（4～5 year）,near mature forest（6 year）,mature forest（7～8 year）,and over mature forest（over9 year）,tree height and diameter at breast height showed a significant positive correlation from young forest to mature forest,but there was no significant difference between mature forest and over-mature forest.There was a significant positive correlation in canopy thickness from young forest to mature forest,but there was no significant difference between mature forest and over mature forest.The proportion of under branches was significantly different in young forest,but there was no significant difference in middle aged forest,near mature forest,mature forest and over mature forest.Canopy width was significantly different among young forests and middle aged forest,but there was no significant difference among near mature forest,mature forest,and over mature forest.The canopy density was significantly different in young forests,middle aged forest and near mature forest,but not significantly different between mature and over mature forest.The coefficient of variation of the height-to-diameter ratio of E.urophylla×E.grandis in classⅢsite was higher than that of class I andⅡsite at 6 years.The average height-to-diameter ratio of the forest stands in descending order of class I,Ⅱ,andⅢsite.The maximum height-to-diameter ratios of the class I,Ⅱ,andⅢsites were 131.6,125.1,and 123.9,respectively,indicating that forest competition occurs at the class site.（4）The growth of the tree height and diameter at breast height of the three site classes increases with the growth of the forest age from the start of growth to the fast-growing peak,post stage of rapid growth and then to the slow or stagnant growth trend,which could be roughly divided into three growth periods and four stages.The proportions of the growth of tree height in the early growth period（0-1 year）,fast growing peak（1-3 year）,post stage of rapid growth（3-7 year）,and near maturity period（more than 7 year）at class I site were21.4%,32.4%,19.7%and 26.5%,respectively.The proportions of the growth of tree height in the early growth period（0-1 year）,fast growing peak（1-3 year）,post stage of rapid growth（3-5 year）,and near maturity period（more than 5 year）at classⅡsite were 21.4%,32.4%,19.7%and 26.5%,respectively.The proportions of the growth of tree height in the early growth period（0-1 year）,fast growing peak（1-4 year）,post stage of rapid growth（4-7 year）,and near maturity period（more than 7 year）at classⅢsite were 20.8%,32.4%,19.7%and26.5%,respectively.The proportions of the increase of DBH in the early growth period（0-1year）,fast growing peak（1-3 year）,post stage of rapid growth（3-7 year）,and near maturity period（more than 7 year）at class I site were 7.6%,21.6%,30.3%and 40.5%,respectively.The proportions of the increase of DBH in the early growth period（0-1 year）,fast growing peak（1-3 year）,post stage of rapid growth（3-5 year）,and near maturity period（more than 5 year）at classⅡsite were 8.5%,22.6%,17.8%and 56.1%,respectively.The proportions of the increase of DBH in the early growth period（0-1 year）,fast growing peak（1-4 year）,post stage of rapid growth（4-7 year）,and near maturity period（more than 7 year）at classⅡsite were 8.3%,31.5%,23.8%and 36.4%,respectively.The intersection point of the annual increase in diameter at breast height and the average annual increase in diameter at breast height was 4.4years.When the volume of E.urophylla×E.grandis pulpwood plantation in southern Yunnan increased to its maximum,the maturity age were 12.5,10.5,and 8.5 years at class I,II,and III site,respectively.（5）There were 93 species of understory plants in E.urophylla×E.grandis pulpwood plantation,belonging to 42 families and 85 genera.Among them,the shrub layer had 22families,32 genera,and 35 species.The herb layer had 30 families,59 genera and 61 species.The species diversity and population numbers of the shrubs and herbs under the E.urophylla×E.grandis pulpwood plantation increased first and then decreased with the growth of the stand age.When the stand grows to the mature forest stage,the total number of shrubs and shrubs under the forest reaches the maximum,and significant changes have taken place after entering the mature forest.In the early stage,the herbaceous species were larger than the shrub species,and the shrub species became larger than the herbaceous species in the later stage.This further reveals that the near maturity period was a critical period when the plant community in the eucalyptus plantation ecosystem could be restored and stabilized.（6）The analysis results of the wood properties of E.urophylla×E.grandis pulpwood plantation in southern Yunnan showed that the basic wood density,fiber length,fiber width and fiber aspect ratio were significantly different in the interaction of site class,stand age and site class×stand age.At 10 years,the average values of the basic density,fiber length,fiber width and fiber aspect ratio of E.urophylla×E.grandis were 0.527 g·cm-1,0.748 mm,20.47μm and36.55,respectively.The average values of basic density,fiber length,fiber width,and fiber aspect ratio of E.urophylla×E.grandis of classⅠsite were significantly higher than those of classⅡandⅢsite.At 10 years,the average basic density of E.urophylla×E.grandis of classⅠsite was 0.525 g·cm-1,which was greater than that of classⅡandⅢsite.At 10 years,the average fiber length of classⅠsite was 0.782 mm,which was greater than that of classⅡandⅢsite.At 10 years,the average fiber width of classⅡsite was 20.69μm,which was larger than that of classⅠandⅢsite.At 10 years,the average fiber aspect ratio of classⅠsite was 38.22,which was greater than that of classⅡandⅢsite.The results of chemical composition analysis of E.urophylla×E.grandis showed that the lignin content and holocellulose content of E.urophylla×E.grandis had extremely significant differences in the interaction of site class,stand age,and site class×stand age.At 10 years,the average lignin content and holocellulose content of E.urophylla×E.grandis were 26.39%and 84.49%,respectively.The lignin content of E.urophylla×E.grandis in the classⅡsite was significantly higher than that of the classⅠandⅢsite,and the holocellulose content of E.urophylla×E.grandis in classⅠsite was significantly higher than that of classⅡandⅢsite.At 10 years,the average lignin content of wood of classⅡsite was 26.70%,which was greater than that of classⅠandⅢsite.At 10 years,the average cellulose content of wood of classⅠsite was 84.84%,which was greater than that of classⅡandⅢsite.Taking the amount of alkali used in the process as 20%,the pulping performance analysis results of E.urophylla×E.grandis showed that there were significant differences in wood pulping residual alkali,kappa number and pulp yield among the interactions of site class,stand age,and site class×stand age.At 10 years,the mean residual alkali and Kappa number were 2.97 and 21.97 g·L-1,respectively,which were higher than those of 5,6,7,8and 9 years.The content of residual alkali and Kappa number in the wood of classⅢsite was significantly higher than that of classⅠandⅡsite.while the pulp yield of E.urophylla×E.grandis was 53.69%at 9 years,which was higher than that of 5,6,and 7,8 and 10 years.At8,9,and 10 years,the pulp yield of classⅠsite was significantly higher than that of classⅡandⅢsite.Therefore,the suitable technological maturity ages for the pulping of E.urophylla×E.grandis at classⅠ,Ⅱ,andⅢsite were 9,8,and 7 years,respectively.At this time,the pulp yield was the highest,the average values were 53.59%,52.27%,and 51.47%,the residual alkali values were 1.74,2.56,and 3.34 g·L-1,and the Kappa number were 18.42,20.41,and21.66 g·L-1.（7）In summary,the determination of the harvest age of E.urophylla×E.grandis pulpwood plantation in southern Yunnan should firstly be based on the purpose of industrial pulping for the purpose of wood,and secondly,consider the properties and volume of wood.Finally,it was determined that the suitable ages for harvesting of E.urophylla×E.grandis pulpwood plantation with classⅠ,Ⅱ,andⅢsite in southern Yunnan were 9,8,and 7 years,respectively. |
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