A stand-level growth and yield model for thinned and unthinned managed Norway spruce forests in Norway

Abstract

A new stand-level growth and yield model, consisting of component equations for stand volume, basal area, survival, and dominant stand height, was developed from a dataset of long-term trials for managed thinned and unthinned even-aged Norway spruce (Picea abies (L.) Karst.) forests in Norway. The developed models predict considerably faster growth rates than the existing Norwegian models. Further, it was found that the existing Norwegian stand-level models do not match the data from the thinning trails. The significance of thinning response functions indicated that thinning increases basal area growth while reducing competition related mortality. No significant effects of thinning were found in the dominant stand height growth. Model examination by means of cross-validation indicated that the models were unbiased and performed well within the data range. An application of the developed stand-level model highlights the potential use for these models in comparing different management scenarios.

A stand-level growth and yield model for thinned and unthinned even-aged Scots pine forests in Norway

“…However, evaluation of long-term behavior based on multiple, subsequent applications of the developed system of equations appeared to be plausible. The development of TPH, BA, and VOL showed logical dependencies on stand age, site productivity, stand density, and management intervention with similar relationships recently reported for Norway spruce (Allen et al 2020). The development of BA over age, for example, followed a sigmoidal curve which after reaching a maximum gradually but slightly decreased (Lembcke et al 2000).…”

“…Similar to other studies relying on long-term forest management experimental trials (Allen et al 2020), observations from sites with lower site productivity were underrepresented in the data used here, in our case this was especially true for older stands. This could be the reason why performance of the developed HT DOM component model was slightly less accurate for the most northerly plots of the study area where lower site productivities prevail.…”

“…After reviewing various approaches (Brooks and Bailey 1992) we followed the procedure presented in Allen et al (2020) to predict stand-level volume. Because the addition of a thinning modifier improved prediction accuracy the equation used here was modified as follows:…”

“…To predict remaining TPH after a thinning intervention when reduction in BA is known only, we used the model in Allen et al (2020):…”

“…As a result, a large number of long-term experimental trials located across the entire country were established to study the effects of thinning on stand-level growth and yield for the main tree species including Scots pine (Brastaad and Tveite 2001). Data from these long-term trials are now available and offer the possibility to dynamically incorporate thinning into growth and yield tools used for practical forest management (Allen et al 2020).…”