Individual-tree growth models for lodgepole pine (Pinus contorta) in Iceland

Abstract

Lodgepole pine (Pinus contorta subsp. contorta) is one of the most important tree species planted in Iceland. The current plantation area is 7100 ha, the first plantations being 80 years old. This study presents models for simulating the development of Icelandic lodgepole pine plantations on an individual-tree basis. The model set consists of a site index model, tree height model, and diameter increment model. Data were collected in 35 permanent sample plots with measurement intervals ranging from 3 to 14 years. The total number of diameter increment observations was 3664. Regression analysis was used in site index and height modelling, and both regression analysis and optimization were tested in diameter increment modelling. An optimization-based model was evaluated to be the most suitable for growth simulations. The use of the developed model set was demonstrated in management optimizations, where the rotation length and cutting schedule were optimized for two young sample plots, one representing poor sites and the other good sites. The optimizations showed that planting is not profitable on poor sites if the discount rate is 4% or higher. The mean annual stem wood harvest was 2.7–4.1 m3ha-1a-1 on the poor site and 8.3–11.7 m3ha-1a-1 on the good site.