Tree Grown Structure In Relation To Width Of Poplar Field Shelterbelts

Shelterbelt is an ecosystem for guarding against natural disasters, adjusting local space micro-climate and improving crops production. It can provide the better preventive function with reasonable forest structure. The structure of shelterbelt is a hot topic in the study of shelterbelt, the main goal of study for shelterbelt is to build shelterbelt system with reasonable structure, functional harmony and remarkable benefit.It could know the variation of leaf and branch characters, tree crown, and shelterbelts to reaseach crown structre in Poplar shelterbelt. Fractal porosity is important index desribed shelterbelt structure and can characterized the structure of shelterbelt more accurately. However, the research about tree crown was just few at present, so, fractal porosity was limited to regulate and manage shelterbelt.to regulate optical porosity of shelterbelt. The optical porosity of shelterbelt was two dimensions index, however, there was deficiency to use the optical porosity express the structure of shelterbelt. With the developing of technical, fractal geometry can characterized the structure of shelterbelt more accurately. It can regulate the structure of shelterbelt and improve protect effect in plain.In this study, Populus×euramericana （Dode） Guinier CL.“zhonglin 46”and Populus×euramericana cv.“74/76”shelterbelts with different age and row were selected in kaifeng country. Thee crown structure were studied based on sample tree selected by different tree order. The main objectives of the paper were to regulate and manage the structrre of shelterbelt. The mainly conclusions as follow:（1） Leaf area Specific leaf area（SLA） was significantly affected by the position in the crown. SLA increased from the top to the bottom of the crown. SAL on individual tree increased with increasing tree age in the same width of shelterbelt, and the order of SLA on individual tree in the same forest age was single row>two rows>triples rows shelterbelts, and triples rows<four rows<stand. This changing might be related to the environmental conditions of tree growth. The results indicated that the SLA of individual tree in P×euramericana cv.“74/76”tree was higher than that in P×euramericana （Dode） Guinier CL.“zhonglin 46”（called Pדzhonglin 46”in short） tree in the same tree age and row. SLA on individual tree in Pדzhonglin 46”forests was 109.3-133.8 cm²·g^-1, and it 135.1-157.8 cm²·g^-1 in P×euramericana cv.“74/76”stands.Leaf area （LA） was also significantly affected by position in the crown. It increased from the interior to the exterior of the crown, and it increased from the top to the bottom of the crown for single row shelterbelt, while, it was higher in the middle than that in the upper and the lower of the crown for two rows, triple rows, four rows and many rows shelterbelts. In addition, LA on individual trees reduced with reducing growth space in the same forest age and row, raised with older forest age in the same row, and it was significantly lower in Pדzhonglin 46”tree than that in P×euramericana cv.“74/76”tree in the same forest age and row. It ranged from 35.02 to 177.75 m² for Pדzhonglin 46”stands, and it varied from 45.35 to 212.94 m² for P×euramericana cv.“74/76”stands.（2） Branch surface area Specific shoot area（SSA） decreased with successively older age classes and increased with sequentially higher branching classes. SSA of individual tree increased with reducing growth space in the same forest age. Furthermore, it decreased with older forest age in the same row. SSA of individual tree in P×euramericana cv.“74/76”tree was higher than in Pדzhonglin 46”tree in the same type. SSA of individual tree in Pדzhonglin 46 and P×euramericana cv.“74/76”shelterbelts ranged from 11.14 to 12.79 cm²·g^-1and 8.72 to 11.92 cm²·g^-1, respectively.Primary branch axis surface area was also significantly influenced by canopy position, and it decreased from the inner to the exterior. But it increased from the top to the bottom in triple rows, four rows and many rows shelterbelts. Lateral shoot surface area decreased with branching order. Moreover, the variation modes for total, primary branch axis, and lateral shoot surface area in individual tree were all the similar as that of LA in a tree. The LA/tree area of Pדzhonglin 46”trees and P×euramericana cv.“74/76”tree were 79.25% and 82.08%, respectively. The branch surface area/tree area of a tree for Pדzhonglin 46”trees and P×euramericana cv.“74/76”tree were 13.63% and 12.81%, respectively.（3） Fractal dimension of the crown The fractal dimension of the crown for 8-year-old tree was greater than that for 6-year-old tree from single, two, and triple rows shelterbelt, conversely, fractal dimension of the crown for 8-year-old tree was lower than that for 6-year-old tree for four rows and more rows shelterbelt. The order of the fractal dimension of the crown in the same forest age was single row<two rows<triples rows< four rows<more rows. Besides, fractal dimension of the crown for P×euramericana cv.“74/76”tree was slightly larger than that for Pדzhonglin46”tree in the same tree age and pattern. Fractal dimension of the crown, calculated based on leaf biomass, ranged from 2.02 to 2.39 for Pדzhonglin46”tree, and ranged varied from 2.18 to 2.63 for P×euramericana cv.“74/76”tree.（4） Shelterbelt structure characters The variation of LAI of stand and LA in a tree was similarly. the variation of branchwood area index, wood area index, and tree area index of stands were also the same, and they all hadn’t remarkably tendency in the same forest age and row, all increased with older shelterbelt age in the same row, and that of Pדzhonglin46”shelterbelt were all lower than that of P×euramericana cv.“74/76”shelterbelt in the same forest age and row.（5） fractal porosity model of Shelterbelt Fractal dimension of Shelterbelt in leafed period(D_f有) was calculate based on total （branch, leaf, and stem） biomass, and that in leafless period(D_f无) was calculate based on branch and stem biomass. Fractal porosity implies occupancy of stands gap to forest volume. Fractal porosity in leafed period and leafless equalβ_f有=3-D_f有 andβ_f无)=3- D_f无 , respectively. Some equations describing the fractal porosity of shelterbelt were developed. Fractal porosity could be described by fractal dimension using the power function model （β_f =αβb） and could be described by stand basal area and relative height to live branch （β_f =α+blnG+ch0）. In addition, some equations for describing the relationship between fractal porosity and LAI, BAI ,WAI ,and TAI were developed（βf =a+bln（ x）+cln（x² ）+dln（x³））. The above model could were used to regulate forest structure.