Study On Site Index Equation Of Cunninghamia Lanceolata Plantations

In this paper, the data of 26-age continuing data of Cunninghamia lanceolata Weimin density experimental stands in Shaowu, Fujian Province was analyzed. Base on the randomicity of the dominant trees in the sample plots with the closing condition, and the microtopography that have an affect on the dominant height growth, we chose four kinds of methods as candidates: the highest-trees-method (methods of the highest 3, 5, 9 15 trees, and shortening as Z3, Z5, Z9, Z15), three-layers-method ( mehtod of 1, 3, 5 heighest trees in every layer and the first 2 trees, second layer 1, third layer trees,shortening as F3,F9,F15 and F5), fixed-dominant-trees method(2 highest trees in every three layers at 6 years old), and the method of average height. We choose seven dominant height growth equation as candidates. And derive 24 difference equation from those equaiton. Then the NLIN process in SAS system was used for equation fitting, and the AutoReg process in ETS module was used for correcting the autocorrelation. After that, the marking method was used for evaluating the equations. And we had the conclusions that:(1) Before and after the base-age (20a), the results of evaluating sites by the three-layer-method are better than others, and the methods of F5 and F9 are the best. The corralation between site index by these two mehod and volume are the heighest 0.780 and 0.778. Considered that the works in stands are very hard, we should measure fewer trees. Then we have the conclusion that the F5 method should be used in the future.(2) Bertalanffy-Richards and Korf equations with floating inflection are better than Logistic and Schumacher equations with fixed inflection point are the two worst ones. So, we think the equations with floating inflection point are better with fixed inflection point for the dominant height data fitting.Among these base equations, the result of the marking method is, Bertalanffy-Richards > Korf > Weibull > Mitscherlich > Gompertz > Schumacher > Logistic, (3) 22 more equations were derived by the algebraic difference approach and generalized algebraic difference approach from base equations. After analysis, we have the conclusion that if the base equation has a good fitting, then the ADA-equations from that have good fittings, too. And the ADA-equations with"b"or"c"as free parameter are worse than that with"a"as free parameter.(4) We can get site index equations from the difference equations, the site index equations from the ADA-equations with"a"as parameter are anamorphic equations with variable asymptotes. And the site index equations from the ADA-equations with"b"or"c"as parameter are polymorphic equations with a single asymptote. However, these two types of site index equations can't reflect the dominant height growth. While the site index equations from GADA-equations are polymorphic equations with variable asymptotes. These site index equations reflect factually the impact of site quality on the dominant height growth. I think that this type of site index equation should be used in the future.