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Forests 2018, 9(6), 368; https://doi.org/10.3390/f9060368

A Flexible Height–Diameter Model for Tree Height Imputation on Forest Inventory Sample Plots Using Repeated Measures from the Past

Department of Forest- and Soil Science, Institute of Forest Growth, University of Natural Resources and Life Sciences, Vienna (BOKU), Vienna 1180, Austria
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Received: 2 May 2018 / Revised: 11 June 2018 / Accepted: 14 June 2018 / Published: 19 June 2018
(This article belongs to the Section Forest Inventory, Quantitative Methods and Remote Sensing)
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Abstract

In this study, height–diameter relations were modeled using two different mixed model types for imputation of missing heights from longitudinal data. Model Type A had a hierarchical structure of sample plot-specific and measurement occasion-specific random effects. In Model Type B, a possible temporal variance was modeled by a sample plot-specific linear time trend. Furthermore, various calibration strategies of random effects were performed on past and current data, and a combination of both. The performance of the mixed models was compared on independent data using bias and root mean square error (RMSE). The results showed that Model Type A achieved the highest precision (lowest RMSE), if sample plot-specific random effects were predicted from old data and measurement occasion-specific ones were predicted from new data. In comparison, however, Model Type B had a higher RMSE, and lower bias. Model performance was almost unaffected from the usage of past or current data for the prediction of random effects. Results revealed that a certain calibration strategy should be simultaneously applied to all random effects from the same hierarchy level. Otherwise, predictions would become imprecise and a serious bias may result. In comparison with traditional uniform height curves, the novel mixed model approach performed slightly better. View Full-Text
Keywords: height–diameter models; mixed models; random effects; calibration strategies height–diameter models; mixed models; random effects; calibration strategies
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Gollob, C.; Ritter, T.; Vospernik, S.; Wassermann, C.; Nothdurft, A. A Flexible Height–Diameter Model for Tree Height Imputation on Forest Inventory Sample Plots Using Repeated Measures from the Past. Forests 2018, 9, 368.

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