Forest Structure and Structural Dynamics of Virgin Beech Forests in Slovakia Article Swipe

European beech (Fagus sylvatica L.) forests gain a special interest in Central Europe. The highly
\ncompetitive species would most likely achieve dominance within a wide range of site conditions.
\nUnderstanding the natural structure and dynamics of beech forests is of great importance for
\nforest ecosystem research from both a conservation and management perspective. Today,
\nthere are only few remnants of virgin beech forests and our knowledge on their structure and
\nespecially on structural dynamics is poor. This thesis focuses on gap dynamics processes, their
\neffect on stand structure and the analytical description of stand structures in terms of forest
\ndevelopment stages in virgin beech forests.
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\nCanopy gap formation is suggested being the main driver of structural processes in in natural
\nbeech forests. However, information on spatio-temporal change of gap pattern, released
\nunderstory structures and their reaction to canopy release are scarce. In the virgin beech forest
\nKyjov a repeated gap inventory was conducted to quantify differences in gap size frequency
\nand fraction over a 10-year interval (2003–2013). Further, the percentage cover of understory
\ntrees and regeneration were estimated in 2013. Gap fraction decreased significantly from 13.6% in 
\n2003 to 8.2% in 2013. Within 10 years the mean rate of gap closure was > 80%. Saplings and 
\ntrees in lower canopy layers formed a heterogeneous understory in large parts of recently formed 
\ngaps. The results indicate considerable variation in disturbance intensity in the past decades. 
\nThe prevalent heterogeneous tree understory guarantees a high resilience to canopy disturbance.
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\nThe effects of gap formation on the regeneration process are fundamental for understanding
\nforest dynamics. There are only a few studies from temperate virgin forests on gap regeneration
\nand its natural dynamics over time and results are partly contradictory. The regeneration
\nstructure was studied in understory gaps of variable size and age, and under closed-canopy
\nconditions in the Kyjov forest. Further, spatial differences in regeneration structure and height
\ngrowth within a gap and in the gap periphery were analyzed. Sapling density and cumulative
\nbiomass were significantly higher in understory gaps than under the closed canopy. Sapling
\ndensity was positively affected by high direct radiation but low diffuse radiation intensities,
\nresulting in pronounced spatial differences in sapling density across a gap. Sapling shoot length
\ngrowth was positively affected by higher levels of diffuse radiation and increased sapling size,
\nwhile direct radiation was not influential. The results suggest that regeneration in small gaps
\nmost likely ends in a suppressed heterogeneous understory while in gaps ≥ 100 m2, regeneration
\nmay be capable even at low plant densities to fill the gap center, often forming a rapidly growing
\ncohort-like regeneration layer.
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\nIt is suggested that in natural temperate forests gap induced regeneration processes imprint on 
\nforest structure in the way that trees establish on the approximate gap area and close the gap over 
\ntime. This assumption lacks an empirical basis. To verify this assumption neighboring trees of 
\nsimilar size were assigned to tree groups on a continuous 12 ha plot in the Kyjov forest and the 
\ngroup size-frequency of such homogeneous patches was analyzed across diameter classes. The 
\nnumber of tree groups (cohorts) in a particular diameter class decreased exponentially as group 
\nsize increased. Compared to random distributions, the Kyjov forest exhibited a more clumped 
\ndistribution especially for small trees. The frequency distribution patterns for group sizes are 
\nsimilar to those for gap sizes reported from the same stand and many others. Even though a 
\ndirect comparison (number of trees vs. m2) is not possible, the results indicate that gap initiated 
\ntree groups may persist through the forest cycle.
\nResearchers defined a succession of forest development stages to explain the diversity of 
\nstructures encountered in beech-dominated virgin forests. However, existing methods based on 
\nempirical stand structural data fail to display structural development comprehensively. A novel 
\napproach for determining the extension of development stages is proposed. The Development 
\nStage Index (IDS) assigns living and dead trees to the Initial, Optimum and Terminal stage 
\naccording to their DBH (7–39 cm, 40–69 cm and ≥ 70 cm, respectively) and quantifies their 
\nextension by means of stem density and basal area. It was applied to 40 spaced sample plots 
\n(500 m2 each) in three beech virgin forests in East Slovakia (Kyjov, Havešová and Stuižca; 120 
\nplots in total). Based on thorough stand structural analyses in the three virgin beech forests, it 
\nis demonstrated that IDS is a promising tool for quantifying the proportion of the three stages 
\non different scales, visualizing the complex mixing of stages and analyzing dynamic changes 
\nin old-growth forest structure. The results from the Kyjov forest derived by the IDS are in large 
\nagreement with the conclusions on how gap dynamics shape forest structure in this forest. This 
\nsuggests that it might be possible to infer on past forest dynamics by analyzing stand structure 
\nwith the IDS.