Search

The combined effects of various disturbance types have lasting consequences on forest ecosystems and the services they provide. We examined inter-specific differences in the responses of European beech, silver fir and Norway spruce to canopy disturbance across four life stages (small seedlings, tall seedlings, saplings and pole-sized trees) in two Carpathian old-growth mixed beech forests located in the Gorce National Park (GNP) and Babia Gora National Park (BGNP), Poland. Both study sites were recently affected by spruce bark beetle outbreak. We compared the composition of tree regeneration between forest plots, canopy gaps and expanded areas (i.e. areas located under tree crowns). Moreover, we studied how various gap properties (size, expanded gap to canopy gap size ratio, shape) and other factors (browsing, plant and advanced regeneration cover) shaped regeneration patterns. Inter-specific differences in species abundance relative to gap properties and intra-specific differences in species response across various life stages to gap properties were found. Gap properties had more pronounced effects on saplings and pole-sized trees than on small and tall seedlings. Gap size had the most noticeable effect on beech across all regeneration classes. However, its effect varied from negative to positive depending on life stage. Pole-sized trees of all species responded positively to gap size. Thus, it seems that large gaps provided an opportunity for all species to recruit to canopy. Fir and spruce responded contrastingly to expanded gap to canopy gap size ratio, which reflects differences in their ability to adapt to high-intensity solar radiation. With the exception of beech, the ‘forest-gap’ gradient only affected trees in the advanced life stages (saplings and pole-sized trees). Beech and fir sapling densities and fir pole-sized tree densities were higher when under forest canopy, but spruce pole-sized trees were slightly more abundant in expanded areas. Browsing rates differed between the two study sites; they were more severe in BGNP, where deer densities in the last twenty years have been significantly higher. This intense deer browsing kept silver fir regeneration below the height of 0.5 m and prevented any recruitment to sapling stage. We conclude that even though the recent spruce mortality caused by bark beetle outbreak improved light conditions in both study areas, thus providing good regeneration opportunities to both beech and fir, deer browsing may have long-lasting effects on successional patterns by hindering fir recruitment in BGNP.

Understanding how species-specific disturbances affect the dynamics of mixed forests is becoming increasingly important due to rapidly changing disturbance regimes. This study estimated the effect of Norway spruce (Picea abies (L.) Karst.) mortality on the disturbance processes in two mixed beech stands of the Western Carpathians that were affected by a bark beetle outbreak. We evaluated the size distribution, fraction of canopy and expanded gaps, the characteristics of gapmakers and the contribution of different species to gap size. The measured canopy gap fraction was

ummary Tree regeneration on coarse woody debris (CWD) is considered to be one the most ecologically valuable aspects of CWD in forest systems. However, most studies have focused solely on uncovering the differences in establishment and growth on CWD (regarded as a homogeneous substrate) in comparison with the forest floor. Our study concentrates on the underlying mechanisms of germinant and seedling colonization patterns and demographic responses relative to various properties of CWD. We analysed the effects of CWD properties (decay class, form, species and diameter) on: (i) germinant and seedling annual counts; (ii) annual germinant and seedling survival; and (iii) seedling growth and height. Our study comprised three species (beech, fir and spruce) over 7-year span in two old-growth stands in the Western Carpathians, and employed generalized linear models and mixed models to test for differences between species. CWD properties affected regeneration at the germination stage. There were some demographic differences between species relative to CWD properties. Decay class had the most pronounced effect on beech, not only on its establishment but also survival and growth. Beech and spruce established and survived in higher densities on beech CWD, while their height growth was enhanced on conifer-derived CWD, particularly on spruce CWD. Stumps enhanced establishment of all species and survival of conifer seedlings. Synthesis. Our study shows that CWD properties do influence seedling establishment, growth, height distribution and survival. Moreover, there may be trade-offs between seedling growth and survival among tree species growing on different species of CWD. This highlights the need to include CWD heterogeneity as a factor that can affect the role of CWD in regeneration in forest ecosystems.

Light is a vital factor affecting tree growth, survival and reproduction. In forests, natural and anthropogenic disturbances are the main drivers of abrupt changes in environmental conditions, including solar irradiance. We examined interspecific differences in the responses of European beech and silver fir to canopy gap characteristics and positions within gaps across various life stages (small seedlings, tall seedlings and saplings) in old-growth stands in Świetokrzyski National Park, Central Poland. Additionally, we analyzed sapling architectural responses to light. Regeneration densities were strongly affected by gap characteristics. The largest interspecific differences in responses to gap characteristics were found for small seedlings, which indicated their different preferences not only for light conditions created within gaps, but also toward various microsites distributed on a fine-scale after gap creation. Small beech seedlings responded only to the position within the gap, but small fir seedlings reacted in a more complex way, including such variables as gap size, shape and distance from a gap border. Gap size and the distance from its border had the most noticeable positive effect on tall seedlings and saplings, indicating that successful transition of regeneration to taller life stages may be possible only in larger gaps and in places further from a canopy border. Light conditions did not affect sapling length to diameter ratio. However, both direct and diffuse light had a negative effect on beech and fir crown area and length. Fir had wider but shorter crowns compared with beech in the whole light spectrum. This result indicates that these two species might have contrasting strategies regarding light interception, with fir being better adapted to increase a crown laterally, and with beech either being more tolerant to self-shading than fir or able to keep a favorable spatial leaf arrangement to avoid self-shading. Beech had the highest height growth increments in low levels of direct light, but its height growth was positively affected by diffuse light. Fir height growth rates showed no response to direct light, but were highest in medium levels of diffuse light. No effect of light on beech height to lateral growth rate ratio was found. The effect of direct light on this parameter for fir was negative, and nonlinear in the case of diffuse light, with the highest ratios observed in medium light levels. Our results stress the need of using both direct and diffuse light when analyzing light effects on sapling architecture.