Co-occurrence of shade-tolerant and light-adapted tree species in uneven-aged deciduous forests of southern Poland

Abstract

This study tested the assumption that in mixed-species deciduous forests, shade tolerance determines the species' role in forming vertical structuring of the canopy layer and that persistence of light-adapted species in such forests is conditioned by the occurrence of larger disturbances and simple vertical structures. Several spatially explicit structural attributes were compared in the neighbourhood of eight tree species (Alnus glutinosa (L.) Gaertner, Carpinus betulus L., Fraxinus excelsior L., Pinus sylvestris L., Quercus robur L., Tilia cordata Miller, Ulmus laevis Pall., Ulmus minor Miller) with different shade tolerance growing in uneven-aged forests. The analysis indicated that although species light requirements were loosely related to the density and structural attributes of the stand patches in which the species occur, the light-adapted species tended to avoid close proximity to the shade-tolerant species. These results suggest that under-canopy trees of light-adapted or mid-tolerant species may survive successfully in heterogeneous canopies in the neighbourhoods of species with similar or higher light requirements. Hence, controlling the admixture of shade-tolerant species may be crucial for the persistence of light-adapted species in uneven-aged forests. The results also indicate that in the mixed-species deciduous forests of Central Europe, complex vertical structures arise not only in larger areas of several hundred square metres but also on small spatial scales corresponding to the projection area of canopy trees and suggest that maintaining species diversity in such forests may not require application of management systems based on extensive canopy openings.

Moderate Diversity in Forest Structure and Its Low Dynamics Are Favored by Uneven-Aged Silviculture—The Lesson from Medium-Term Experiment

“…This corroborates the earlier observations [22]), pointed out that the growing stock of uneven-aged forests on fertile sites should be over 400 m 3 ha −1 . However, tree density, basal area, and growing stock can vary significantly in forests managed according to the selection system depending on their location [10]. Similar density and total basal area were reported in uneven-aged forests consisting of shade-tolerant tree species in Serbia, with the highest proportion of silver fir [23].…”

“…Our results generally confirmed the supposition that species composition of forests treated with selection system is dominated by shade-tolerant tree species and that dominance will be rather maintained. Other tree species, including light-demanding species, form an admixture but in different proportions [9,10,25]. While the selection system seems to be especially suitable for shade-tolerant species, there are some examples of implementation of this system in forests consisting of light-adapted species.…”

“…Favorable conditions for the hornbeam in the absence of human activity have been reported in [27]. Other studies stated that the persistence of shade-tolerant, mid-tolerant, and shade-intolerant tree species is possible in uneven-aged forests for two main reasons: one is the fact that these groups of species may occur in different stand layers; the other is human interventions controlling the mixing of different groups of species [10]. As results showed, more light-adapted tree species tend to avoid the neighborhood of shade-tolerant tree species, but can survive around species with similar light requirements [10].…”

“…While uneven-aged silviculture is usually applied in silver fir-dominated forests, there are examples of its application in forests consisted of tree species with quite different light requirements [6,[9][10][11][12][13].…”

“…In such multispecies uneven-aged forests, the combination of even-aged silviculture (small clear-cuts in gaps) with single-tree selection (uneven-aged silviculture) can be highly recommended to provide the suitable conditions for wide range of tree species, for light-adapted, mid-tolerant, and for shade-tolerant species, and to maintain them as structurally diverse forests [8,10].…”