Site-specific height-diameter and stem volume equations for Lebombo-ironwood


  • Tarquinio Mateus Magalhães Universidade Eduardo Mondlane



Fixed-effects, Random-effects, Dummy variables, Androstachys johnsonii Prain


Height–diameter (H–D) and stem volume equations are indispensable tools for forest management and have a wide use in forestry, however they are lacking for Lebombo-ironwood. Based on a dataset of 1144 Lebombo-ironwood trees destructively measured for height and stem volume, H–D and stem volume models were fitted using mixed-effects and dummy variables models. Random-effects and dummy variables were the different growing sites, as they affect H–D relationships and therefore stem volume models. Different model forms were compared to each other with regard to the sources of errors. The error due to uncertainty in the model parameter estimates was insignificant for mixed-effects models, whilst the error due to model misspecification was relatively larger for dummy variables H–D functions when compared to the mixed-effects ones. However, both mixed-effects and dummy variables models were similar in terms of error due to residual variability around model prediction. Overall, mixed-effects and dummy variables models did not differ in terms of predictive ability and accuracy.


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