Density and spatial distribution of beech (Fagus sylvatica L.) regeneration in Norway spruce (Picea abies (L.) Karsten) stands in the central part of the Czech Republic

Abstract

Abstract: The conversion of Norway spruce monocultures to mixed forest is a long-term and costly process, and little information is available on the silvicultural use of spontaneous regeneration of native tree species to such purposes. In this context, we focused on the natural expansion of European beech in pure Norway spruce stands currently occurring in central Europe. The study was conducted in three secondary spruce stands with single adult (seed) beech trees growing on acidic sites of the fir-beech vegetation zone in the Bohemian-Moravian Highlands (Czech Republic). The regeneration strategy of beech and spruce (in terms of density and height increment) was studied under different light regimes (expressed using the indirect site factor - ISF) on the forest edge (9.7-41.2% ISF) and within gaps in the forest interior (10.7-20.8% ISF). Beech showed a broad light adaptability, being present under the spruce canopy with high density, depending on the distance from beech seed trees. Sparse beech saplings were found at a distance of more than 100 m from adult beech trees; however, abundant beech regeneration was found up to a distance of 25 m. Contrastingly, the density and growth in height of the spruce regeneration was strongly affected by light conditions. Spruce reached a density higher than beech in the understory where ISF > 17% (i.e., up to a distance of 45 m from the stand edge or within gaps no smaller than 400 m2), and competed with beech in terms of height growth where ISF > 20% (i.e., at the very stand edges). Knowledge of the spatial pattern and the light strategy of both species provided useful information to support the conversion of spruce monocultural stands to mixed spruce-beech forests.