Finnish Forest Research Institute  Metla

Media release 06.05.2005

Evaluation of performance of tree-level biomass models for forestry modeling and analyses

In her doctoral thesis within the field of forestry, Leena Kärkkäinen, M.Sc. (Agriculture and Forestry), evaluated the performance of the available tree-level biomass models for forestry modeling and analyses. Knowing the biomass of a tree is necessary, for example, in order to estimate the amount of carbon sequestered by trees and the amount of energy wood resources.

The comparison of several different biomass models indicated that the Marklund’s models developed in Sweden are currently the most applicable ones for the estimation of the biomass of the different tree components. Although the data for the derivation of Marklund’s models was collected in Sweden, the models are considered valid for Finland as well. However, the reliability of the calculated results was largely dependent on the structure of the stand. The models are at their best in well-managed pine-dominated stands. With regard to single components of a tree, the biomass models are the most applicable for the estimation of the biomass of the stem wood and the stem bark. The performance of the models in terms of the biomass of stem wood and stem bark is realistic as regards the location and the fertility of site, but much more uncertainty is involved in the estimation of biomass of other components of a tree.

The research indicated that the Marklund’s models are more applicable for the estimation of carbon sequestration of the above-ground components of trees than for the estimation of energy wood resources. This is due to the fact that most of the above-ground biomass consists of stem wood, for which Marklund’s models produce realistic outputs, whereas energy wood mostly consists of living branches, for which the results of the models are less reliable.

Usually the models have been tested only against the empirical testing data using statistical tests. Measuring the mass of the different tree components is, however, very tedious and expensive and hence, representative empirical data is not available. For the same reason, even though earlier studies were available on the carbon balance and energy wood resources based on tree-level biomass models, no previous studies were available on the applicability of the models to the estimation of biomass of growing stock in different growing conditions.

In this study the models were incorporated into Metla’s MELA forest planning system, which is widely used in Finland for supporting the decision-making in forestry. The MELA system was used to analyze the applicability of the models to stand-level and large-area level forest calculations. The evaluation methods applied in the study were used to determine deficiencies in the model structure and the performance of the models at different application levels (tree, stand, forest area). The evaluation of the models could also be used to identify the lack of current knowledge. The study showed that application of statistical tests is not the only way to gain useful information on the performance of the models.

Ms. Kärkkäinen defended her dissertation on Saturday, May 7, 2005 at 12.00 in Auditorium Käpy, Metla building, Joensuu
Publication: Evaluation of performance of tree-level biomass models for forestry modeling and analyses, Metsäntutkimuslaitoksen tiedonantoja 940

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