Site Index Models for Main Forest-Forming Tree Species in Poland

Jarosław Socha,Ewa Grabska,Stanisław Orzeł,Luiza Tymińska-Czabańska

doi:10.3390/f11030301

Jarosław Socha, Ewa Grabska + Show 2 more

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https://doi.org/10.3390/f11030301

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Abstract

Site index is the most commonly used measure of potential site productivity, providing key information for forest management practices. It is determined using species-specific site index models that take into account climatic and edaphic factors. To reliably estimate the site index, appropriate models are necessary. In Poland, however, outdated guidelines, i.e., yield tables, are used to determine site classes, which result in the inappropriate estimation of height growth and increments of stands. Therefore, the aim of this study is to develop new site index models for the main forest forming tree species in Poland, in a total of eight species. For the development of site index models, we used growth trajectories of 3052 sample trees, representing the whole range of geographic locations and site conditions. Five dynamic models were selected and parametrized to develop the site index models. The models were evaluated using quantitative measures of goodness of fit (MAE, R2, and AIC), the analysis of residuals, and the assessment of how the model reflects the biological phenomena of height growth. Results showed that depending on the species, different models have the highest predictive ability. There are significant differences in results using traditional yield tables and developed site index models. For most of the species, the largest differences characterized either the youngest or the oldest age classes. These differences can be attributed to the changes in growth conditions from the time when yield tables were developed. Growth dynamics of forest stands may also show spatial variability, thus, in future research additional site variables and, regional variability should be taken into account.

Highlights

Information concerning site productivity remains a fundamental variable in forestry [1,2,3,4].The unbiased estimation of site potential is essential for forest management because it is the main determinant of species-specific decisions, connected with the selection of silvicultural treatments, species composition, and the determination of the allowable cut and rotation periods [3,5,6]
Compared to the methods still used in Polish forestry practice, such as yield tables, our models provide better predictive ability, which was reported by many other studies that applied the generalized algebraic difference approach (GADA) methodology, for instance [47]
We have developed new site index models for eight of the main forest-forming tree species in Poland, namely Scots pine, European beech, black alder, European larch, silver birch, oak, Norway spruce, and silver fir, using over 3000 data series describing the trajectories of tree height growth

Summary

Introduction

Information concerning site productivity remains a fundamental variable in forestry [1,2,3,4]. The unbiased estimation of site potential is essential for forest management because it is the main determinant of species-specific decisions, connected with the selection of silvicultural treatments, species composition, and the determination of the allowable cut and rotation periods [3,5,6]. Site productivity is one area of strategic information in forest management, which determines the economic and environmental effects of forest management [6,7] and allows the forecasting of stand growth [2]. Site index models are the main functions used in the empirical models of tree stand growth [11,12,13].

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