基于树木起源、立地分级和龄组的单木生物量模型

Abstract

Individual tree biomass models were developed by tree origin,site classes and age groups of Pinus massoniana and Larix.Model validation was implemented using independent data.Two allometric equations,which were compatible to stem volume,were fitted by ordinary least square and two methods of weighted least square.Models for above-ground biomass,its component biomass and below-ground biomass were analyzed and evaluated through several important statistics such as coefficient of determination,root mean square error,total relative error and estimation accuracy.The results showed that above-ground biomass models of Pinus massoniana and Larix were best for fitted results and validated results by classified sites.Variable allometric ratio models is better for Pinus massoniana,while constant allometirc ratio model is better for Larix.Two methods of weighted least square showed different performance for model calibration and validation.Weighted regression No.2 model(weighted function 1/f 0.5) was better for calibration data than Weighted regression No.1 model(weighted function 1/y0.5),however,the latter was better for validation sample than the former.The No.1 model presented best results for both construction and verification sample compared with ordinary least square. Models of components of above-ground biomass of Pinus massoniana and Larix gave same performance order on fitted and validated results,with best estimation for stem biomass,worst for leaf biomass and moderate for branch or bark biomass.Effects of sample classification method,two allometric equations and methods of weighted least square on stem biomass were same as that of above-ground biomass.With best combination of sample classification,allometric equations and methods of weighted least square,the total relative errors of biomass models were less than ±10.0% for branches,±5.0% for barks and±30.0% and ±20.0% for leaves of Pinus massoniana and Larix,respectively. Comparing with base models,below-ground biomass models of Pinus massoniana and Larix by classified age groups,which were compatible to above-ground biomass and stem volume,respectively,had significantly improved on coefficient of determination and estimation accuracy,especially,the models for Larix raised more than 6% in coefficient of determination,more than 3% in estimation accuracy.In general,the model compatible to stem volume was better than the model compatible to above-ground biomass.The test results by above-ground biomass and stem volume of large sample data confirmed the same regular pattern.