Studies On Growth Analysis And Economic Benefits Evaluation Of South-type Poplar Stands In Different Densities In Hubei Province

By using the method of mean tree investigation, 76 standard plots withl7 planting densities at SI 18-20 in 15 counties and cities in Hubei province were investigated in this paper. On the basis of poplar stands (at age of 5-13) investigational data, Volume increments of singular tree and stand were calculated, optimum rotation age of poplar stands with different densities was determined and economic benefits of poplar plantation were analyzed and compared. By the regression analysis, the best growth prognosis models of poplar stands were selected from 7 kinds of growth models (such as Mitscherlich Model, Logistic Model etc.) which were used to simulate the growing dynamics of DBH and height. The comprehensive effects of density on the growth of poplar plantation were analyzed and the optimum felling ages (rotation ages) with different densities and site indexes and the optimum were selected. The optimum densities in SI 18-20 were determined on the basis of economic benefits. The results showed:(1) The best growth prognosis models of DBH and height all are y=a x~b e~-cx.(2) The volume increment of singular tree does change obviously during the infancy (at the ages of 1~3), but with the aging, they differ greatly in different densities. While the density increasing, the increment volume of singular tree is decreasing. So does the average annual volume increment of singular tree. The ages, at which the summit of the average annual increment and cunent annual increment of singular tree volume appears, moves up with density increasing.(3) The volume increment of stands with different densities differs greatly. While the density increasing, the total increment volume of stands is also increasing. So does the average annual volume increment of stands.(4) The optimum rotation ages with densities in1.5m×1.5m~3m×3m are at the ages of 6~8 for producing the small-diameter lumber, those in 3m×4m~5.5m×5.5m , 9~llfor producing the mid-diameter lumber ,and those in 6mx8m~10mx8m., 12~ 14for producing the large-diameter lumber.(5) In SI 18 ~20, the densities, with which the economic benefit of the plantationis good, are in middle and high degree, especially in 3mx4m, mainly, for producing small-diameter lumber and mid-diameter lumber. However, though the plantations which their density is in the low degree such as 6mx8mN 8mx8nu 8mxl0m,etc.may get some money, the afforestation risk increases because of the low productive potentialities and the low IRR..