Relationships between Structural Indices and Conventional Stand Attributes in an Old-Growth Forest in Southeast Europe

Srđan Keren,Pavel Janda,Miroslav Svoboda,Thomas A Nagel

doi:10.3390/f11010004

Abstract

Structural indices are often proposed as guiding measures for increasing structural heterogeneity. However, few studies have examined the association between such indices and conventional stand attributes. The primary objectives of this study were to evaluate changes in structural heterogeneity and tree species diversity at different plot sizes and to quantify the relationships between conventional stand attributes (mean tree diameter, absolute tree density, basal area, species proportion) and structural indices in a mixed old-growth forest in Southeast Europe. Paired tests were used to identify significant changes in structural heterogeneity with increased plot area, while the relationships between stand attributes and analyzed indices (Gini, diameter differentiation, species mingling, and Shannon’s index) were evaluated with Pearson’s correlations. The index values of Gini, diameter differentiation, and tree species mingling were rather stable with the increase of plot size, whereas tree species diversity increased significantly with the increase of plot area from 200 m2 to 1500 m2. The measures of tree species mingling and tree species diversity were strongly associated with each other, while their association with diameter variability was weak to moderately strong. Tree species mingling index was strongly associated with the changes in tree species proportions. However, conventional stand attributes were generally not strongly correlated with the examined indices. For restoring and maintaining old-growth characteristics, forest managers may use structural indices to increase small-scale structural heterogeneity, tree species mingling, and diversity, but only as an additional set of measures, not as surrogates for conventional stand attributes.

Highlights

For both conservation and commercial reasons, the characteristics of forest stand structure are of great interest to various groups of stakeholders, including forest managers, scientists, ecologists, and decision makers
The distribution of trees based on diameter at breast height (DBH) has been conventionally used to describe stand structure, including that of unmanaged forests [3,4,5,6,7]
Quantifying small-scale structure is of importance to forestry practitioners when the goal is to manage a forest by emulating the small-scale DBH variability and tree species mingling patterns found in old-growth forests

Summary

Introduction

For both conservation and commercial reasons, the characteristics of forest stand structure are of great interest to various groups of stakeholders, including forest managers, scientists, ecologists, and decision makers. This includes very small areas in which the interactions among neighboring trees occur. Such scales often correspond to the sizes of small inventory plots (e.g., up to several hundred square meters) depending on the research interests [10]. Forest researchers are often interested in scrutinizing DBH variability at the small-scale level within a stand for the purpose of examining its potential association with tree species diversity. Such investigations have mostly been conducted in managed forests [11,12] and are lacking for old-growth forests

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Conclusion