From branches to crown : development of crown biomass models for intensively treated stands of loblolly pine with mixed effects models
De los Santos-Posadas, Hector Manuel
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The flexible characteristics of mixed effects models are adapted in a pure allometric context to develop precise estimates of needle and woody biomass on intensively treated stands of loblloly pine. First, reliable estimates of branch biomass were developed using multilevel mixed effect structures in a linear and nonlinear context. The method proved to increase the accurcy of branch level wood and needle biomass estimates and as a result total tree estimates of branch and needle biomass are quite different when compared with estimates from models using fixed global parameters. At the tree level use of foliage distribution theory to generate foliage and woody biomass equations for tree crowns, as defined by Zhang et al (2003), is adjusted and generalized to include other more flexible model forms. Tree level foliage and woody biomass is modeled using the Chapman-Richards and Schumacher growth curve derivatives as the underlying basic biomass distribution functions. The models produced proper estimates when used to model total needle and woody biomass in crowns of intensively treated stands of loblolly pine in Georgia. Finally combining fractional crown biomass models with compatible complete crown biomass derived equations it is possible to simultaneously estimate total tree content and foliage distribution. The approach is easily extended to the crown woody components and the models were successfully fitted with a mixed effect model structure allowing good variability control and reliable parameter estimates.