Abstract
The use of natural regeneration techniques is one of the key elements of modern (close-to-nature) forestry. In natural forests, changes in canopy cover, such as the emergence and successive re-closure of canopy gaps are particularly important, as they influence the light availability on the forest floor. Creating canopy gaps of different size is a promising silvicultural tool allowing the regulation of the light availability in managed forests in order to control regeneration composition and development. In this study, we used terrestrial laser scanning data to investigate the relationship between canopy-gap dimensions and emerging natural regeneration along a gradient of management in forests dominated by European beech (Fagus sylvatica, L.). We analyzed the spatial distribution and height of regeneration patches in dependence of gap characteristics. Mean regeneration height decreases progressively from the gap polygon over a transition zone towards the area under the canopy, while the tallest regeneration plants were placed in positions midway between center and gap edge, and not directly in the gap center as we initially assumed. The centers of regeneration patches were not displaced when compared to the associated canopy gap centers, as has been reported in other studies conducted on the northern hemisphere for various tree species. The observed patterns did not depend on management strategies, indicating that regeneration responded equally to naturally created gaps and gaps that were caused by logging. We conclude that establishment and development of shade-tolerant European beech regeneration in forest stands is driven by gap openings, but not necessarily direct radiation. If at all, pronounced direct radiation mainly occurs at the northern edge of large gaps. Neither regeneration patch center, nor regeneration tree height pointed in that direction. Our study suggests that in the investigated beech-dominated forests the effect of increased light availability at the northern edge of a gap is overruled by other factors increasing towards the gap edge, such as increased belowground competition of the overstory trees.
Highlights
An essential part of modern, close-to-nature silviculture is imitating natural forest dynamics and integrating natural processes, such as natural regeneration [1,2]
Canopy gaps are not static, but change their size and shape over time as they progressively close through horizontal ingrowth of gap-neighboring trees or vertical ingrowth of understory juvenile trees emerging in the gap [4,5,7,8]
We found no significant differences in gap size of naturally and artificially created gaps caused by logging in the managed forests
Summary
An essential part of modern, close-to-nature silviculture is imitating natural forest dynamics and integrating natural processes, such as natural regeneration [1,2]. When considering natural forest development, the dynamics of canopy gaps play a major role, as they determine the light availability. The distribution of light is one of the most crucial abiotic factors, as it does affect regeneration dynamics, but it allows foresters to direct forest development through light-regulating interventions [5,6]. Small gaps are closed within a few years, while larger gaps often expand subsequently due to the death of neighboring trees [4,9]. This leads to a constant change in light availability for lower canopy layers and regeneration
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