Interspecific effects between overstorey and regeneration in small-scale mixtures of three late-successional species in the Western Carpathians (southern Poland)

J Paluch,L Bartkowicz,W Keith Moser

doi:10.1007/s10342-019-01209-y

Abstract

In mixed-species forests, species composition of the overstorey affects regeneration processes through its influence on seed rain intensity and micro-site characteristics. Based on extensive inventory data (1583 sample plots), this study investigated relationships between the percentages of silver fir (Abies alba Mill.), European beech (Fagus sylvatica L.), and Norway spruce (Picea abies (L.) H. Karst.) in the overstorey and in naturally established regeneration (seedlings of a height below 0.5 m). A useful framework for this analysis was the assumption that for a given stand density level expected seedling density increases approximately linearly with the increasing percentage of conspecific trees because of increasing seed supply. The analysis partly disproved this assumption and indicated that the species’ proportions in the overstorey and regeneration change in a nonlinear manner. In the beech–fir and beech–spruce mixtures, a strong tendency for beech regeneration to increase its proportion was found in the stands with similar percentages of the species. Fir regeneration positively responded to the presence of beech and spruce in the overstorey; an over-proportional increase in fir percentage was found in stands with more than 60% of beech and, depending on stand density, in a wide range of mixture variants with spruce. These effects may be viewed as increase-when-rare mechanisms that limit superior competitors and counteract the transformation of mixed-species stands into monocultures of spruce or beech. The analysis indicated that reduced stand density considerably facilitates establishment of spruce regeneration in the mixtures with fir and beech, but decreases the percentage of fir regeneration in the mixtures with beech.

Highlights

The species that build multi-species forest communities are frequently characterized by distinctive adaptations and strategies that increase the probabilities of their populations continuing in the presence of other co-occurring species
The generalized linear models (GLM) analysis confirmed this complex effect of beech percentage and the negative effect of stand density on beech seedling density (Table 3), the predictive power of these variables was modest (Nagelkerke pseudo-R2 = 0.05)
The relative density of fir seedlings clearly increased with the decreasing proportion of fir in the basal area but was independent of stand density (Fig. 2)

Summary

Introduction

The species that build multi-species forest communities are frequently characterized by distinctive adaptations and strategies that increase the probabilities of their populations continuing in the presence of other co-occurring species. In the case of late-successional species, which regenerate mostly in small canopy gaps or in the shelter of adult trees, one determinant of site heterogeneity is the density and species composition of the canopy layer (Ujházy et al 2017). Both of these variables influence light availability, physical and chemical topsoil properties, and water accessibility (Barbier et al 2008). They influence the biotic environment from soil microorganisms. Root exudates and hyphal linkages to trees and other plants may condition the abundance of soil fungi (Frankland 1998) and enhance mycorrhiza colonization rates (Cline et al 2007) or seedling mycorrhiza diversity (Grebenc et al 2009)

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