Basal Area Growth And Model Prediction In Cunninghamia Lanceolata(Lamb.) Hook. Plantations

Basal area growth system is a key componmet of stand-level models, since basal area is directed related to other very important variables.In this paper, relationship between basal area and stand factors, which is based on spacing and thinning trials at whole- stand, size-class and individual tree levels at the Chinese fir plantations.Stand basal area growth trends with spacing trials have shown at the initial same growing space or site indexes; variance analysis is used to explain stand density effect; Richard'model was chosen as the cumulative stand basal area function and the ages of the growth curves inflection points were found by determining the age at which the second partial derivate of the Richard'model; regression analysis is used to illustrate relationship between stand basal area growth rate and stand density, site quality.Inspection of these data revealed that stand basal area is well correlated with stand density, site quality. The cumulative stand basal area and growth rate increase progressively with increasing initial density and better site quality.The age at which the growth rate culminates increases as initial stocking density decreases. After culmination the growth rate declines much faster for higher stocking densities, causing the growth rate for the higher densities to drop below those for the lower densities. Stand basal growth rate decreases at competition stage, while cumulative stand basal area increases slightly. When stand growth reaches a dynamic stable balance, the cumulative stand basal area converges to one at a certain initial stand density level. Self-thinning has no begin under a certain initial stand density level.At the same stand density, the low site index lead to high natural mortality. Stand density become from low to high, when the snag basal area reaches the maximum value early.The higher stand density, snow damage is higher; the higher site index, snow damage lower. Compared with the low slope, snow damage ratio is larger at the high slope.Thinning indiciates: after thinning was done, the different size-class logs can be gained and the remained trees growth is promoted. When trees were planted with higher site and stand density, the small size-class timber was gained. Above a certain stand site, the cumulative stand basal area between thinned and unthinned converges to one.Three well-known growth functions (Korf, Hossfeld and Bertalanffy-Richards) were considered for developing a stand basal area growth system for the different spacing and thinning artificial trials. Among the ten dynamic equations finally evaluated for basal area projection, the Generalized Algebraic difference Approach (GADA) formulation from the Korf equation that considered parameters a1 and a2 to be site specific was selected. The concrete formulation is fllowing:The basal area erroris is in proportion to diameter class and inversein proportion to mean diameter. That is P_S = ( a/2d)~2(%).The results were showed with basal area at the size-class level that (1)well relationship between size-class and simulation precision; (2) compared with R a2dj, Root MSE and RSS, Champan-Richards'has the higher precision gains than those, then Richards', Weibull (3 parameters) and Logistic. Furthermore, the interval estimation with the model parameters also proved to the identical results; (3) applying size-class cumulating method, the asymptote value equals to 1. As a result, the number of the model parameters decrease and the estimated results is parallel with that the parameters is unequal to 1; ( 4) the model stability was gained by relationship between model parameters and stand factors: Weibull(3 parameters)higher, then Logistic, Richards'and Champan-Richards'.The results were showed that snow damage didn't changed individual tree growth trends using Chow test with spacing and thinning artificial trials. The panel data provides a useful model of individual tree basal area grow trends. (1) the basal area increment is well correlated with site quality; (2) at a certain site index level, the basal area increment decreases while stand density increases; (3)by adding competition indexes, the basal area growth outperforms; (4)thinning decreases inter-individual tree competition and makes the remained trees gain enough growth resource.