A tree crown ratio prediction equation for eucalypt plantations

Based on a data set from spacing trials and permanent plots of Eucalyptus globulus Labill., several nonlinear equations for crown ratio prediction (based on exponential, logistic, Richards and Weibull functions) were tested. The total data set was used to fit and select the equations. The equations were evaluated in terms of measures of fit and prediction ability: adjusted-R 2 , residual mean square, sum of PRESS residuals and sum of absolute PRESS residuals. The normality of the studentized residuals was analyze d using normal QQ plots. The presence of heteroscedasticity associated with the error term was checked by plotting the studentize d residuals against the predicted values. The significance of the estimated parameters was verified. Model error was characterize d in terms of bias and precision. The Richards function was selected. This equation is age and density dependent, reflecting the imp or- tance of intertree competition; an initial tree dimension and a measure of stand productivity were also required as explanatory vari- ables.

[1]  Harold E. Burkhart,et al.  Relationships between tree crown, stem, and stand characteristics in unthinned loblolly pine plantations , 1987 .

[2]  H. White.  A Heteroskedasticity-Consistent Covariance Matrix Estimator and a Direct Test for Heteroskedasticity , 1980 .

[3]  Martin W. Ritchie,et al.  Equations for predicting height to crown base for fourteen tree species in southwest Oregon , 1987 .

[4]  Harold E. Burkhart,et al.  Compatible crown ratio and crown height models , 1987 .

[5]  R. Monserud,et al.  A basal area increment model for individual trees growing in even- and uneven-aged forest stands in Austria , 1996 .

[6]  S. Linder,et al.  Optimization of Biomass Production in Eucalyptus Globulus Plantations. — A Case Study , 1989 .

[7]  Nicholas L. Crookston,et al.  User's guide to the stand prognosis model / , 1982 .

[8]  Margaret R. Holdaway,et al.  Modeling Tree Crown Ratio , 1986 .

[9]  H. Burkhart,et al.  Modeling individual tree growth for juvenile loblolly pine plantations , 1996 .

[10]  G. Somers,et al.  Methods for Modeling Individual Tree Growth and Stand Development in Seeded Loblolly Pine Stands , 1979 .

[11]  R. H. Myers.  Classical and modern regression with applications , 1986 .

[12]  Hubert Hasenauer,et al.  A crown ratio model for Austrian forests , 1996 .

[13]  K. J. Mitchell,et al.  Dynamics and Simulated Yieldof Douglas-fir , 1975 .

[14]  Gary J. Brand,et al.  A description of STEMS-- the stand and tree evaluation and modeling system. , 1982 .

[15]  Jerome K. Vanclay,et al.  Modelling Forest Growth and Yield: Applications to Mixed Tropical Forests , 1994 .

[16]  Craig G. Lorimer,et al.  Predicting tree growth from crown variables in managed northern hardwood stands , 1994 .

[17]  Leaf area estimation from three allometrics in Eucalyptus globulus plantations , 1997 .

[18]  Harold E. Burkhart,et al.  Predicting Crown-Height Increment for Thinned and Unthinned Loblolly Pine Plantations , 1992, Forest Science.

[19]  Harry T. Valentine,et al.  Modeling crown rise in even-aged stands of Sitka spruce or loblolly pine , 1994 .

[20]  Oscar García,et al.  Evaluating forest Growth Models , 1997 .