《Table 2 The fitting results of the growth of 77-year-old P.densiflora using the empirical equation

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《Effects of Light on Tree Growth》

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In this paper，the 77-year-old sample tree was taken as the example for the analysis of the research method.The data of the parse wood was used to establish the empirical equation of tree growth amount and tree age.D2-0was used to represent the ground diameter，D2-0.5was used to represent the tree diameter at the height of 0.5 m，and so were the others.H2was used to represent tree heights，and V2the tree volumes.Y（t）was the function with time（tree age）as the independent variable and growth amounts of various tree indicators as the dependent variables.The empirical equations y=exp（a+bx）and y=exp（a-b/x）were used to establish the digital regression equation.Calculated using a spreadsheet，the test results were shown in Table 1，2，3 and 4.All items passed the R-test，F-test，and t-test，and the fitting accuracy all reached 99.99%.DBH（tree diameter at the tree height of1.3 m）in Table 2 and most items in Table 4 all had the test accuracy being infinitely closed to 100%.The double time in Table 1and 3 was the time needed to double the tree growth amount，which was used to express the tree growth rate in a more clear way.As shown in Table 1，the increase of wood volume was the fastest，while in Table 3 the increase of tree diameter at 5.0 m was the fastest.In Table 2 and 4，tmand tzwere the first and second derivatives of the function y（t）=exp（a-b/t）.The former was the maximum average growth rate of the tree growth index at the moment，while the latter was the maximum immediate growth rate，and the former was twice of the latter.The high accuracy of the test suggested that the selected method and test data had scientific rationality and accuracy.Hundreds of scientific experiments had been made，and all showed the suitability of the equations，so no similar tests were made to the suitability of the equations.