Models for predicting individual tree height increment and tree diameter in young stands in southern Sweden

Abstract

Individual tree height increment functions and general diameter–height relationships were developed for Scots pine (Pinus sylvestris L.), Norway spruce [Picea abies (L.) Karst.] and birch (Betula pendula Roth and Betula pubescens Ehrh.) trees growing in young stands in southern Sweden. A random parameter approach was applied to account for the spatial correlation in the data. Variables for initial tree size and measures of both stand density and relative competitive status were common to all sets of functions. Data for constructing the models were collected from the HUGIN young stand survey, a large survey of young forest stands. The validation procedures indicate that the models give reliable estimates of tree height and diameter up to an average tree height of at least 15 m. However, height growth of birch in mixtures with conifers was slightly overestimated, probably because damage was not considered in the growth forecasts. The diameter of spruce was underestimated for regularly spaced experimental plots.

Keywords:

• Diameter–height relationships
• height increment
• individual tree model
• mixed model
• young stand

Acknowledgments

We are grateful to, and wish to thank, Professor Urban Nilsson and Associate Professor Per-Magnus Ekö for helpful and constructive criticism of the manuscript. We would also like to thank Morgan Erixon and Nils Pettersson for providing validation data. We are indebted to Sauli Valkonen and an anonymous referee for their thorough review of the paper and many helpful suggestions. This study was partly funded by Mistra, through the research programmes SUFOR and Heureka, and by the Brattås foundation.