Reconstruction of the growth dynamics of primary beech-dominated forests in Central Europe using dendroecological methods

Ing. Michal Frankovič

Doctoral thesis

Abstract:

Natural disturbances are critical factors in forming forest ecosystem structure and dynamics. Investigation of disturbance regimes' spatial and temporal extent is critical for understanding forest structural heterogeneity, biodiversity habitats and development stages. Quantifying disturbance regimes is, therefore, imperative for the appropriate management of forests and protected areas. However, natural disturbance regimes have rarely been assessed using dendrochronological methods on a regional scale across primary mixed beech-fir forest stands. To study the natural disturbance regimes of beech-dominated mixed-forest stands, we established numerous permanent study plots with an area of 0.15 ha across primary forests in the Carpathian Mountains, which still contain large areas of primary forest. We reconstructed the plot and stand-level disturbance history using a tree-ring-based approach. The temporal synchronicity of disturbance events was then evaluated by delineating stand-level disturbance events using a kernel density function and detecting plot-level disturbances with severities greater than 10 %. The results obtained from the chronologies showed substantial variability in time and space. Our main objectives were to reconstruct the natural disturbance regime in mixed beech-fir forests - one of the most dominant forest vegetation types in Europe - in the Carpathian Mountains, with aims to describe how historical processes influence forest dynamics and structure. Further, we evaluated disturbance synchronicity in time and disturbance synchronicity – species composition relationship. We aimed to: i) Estimate the range of past disturbance activity, as well as quantitatively describe the spatial and temporal variation in disturbance frequency and severity across the study stands. ii) Understand which type of disturbance regime - gap dynamics, intermediate-severity or high-severity disturbance regime - most affects the study plots on the spatial scale. iii) Determine the difference in the temporal and spatial extent of the disturbance regimes in the Western and Eastern Carpathian regions. iv) Explain the species-specific relationships between tree species composition and the temporal and spatial extent of natural disturbances. Our results are: i) A detailed description of the past 250 years long disturbance history, where a wide variation of disturbance events was found. Disturbances affected several plots simultaneously over short periods, thus creating a coarse-grained forest structure. The disturbance regime was characterised by substantial variability in time and space, with fluctuation, especially in the mid-19th century. Low and moderate-severity plot-level disturbance events were most common, but high- and extremely high-severity plot-level disturbance events also occurred. The observed spatial and temporal variability suggests that the beech-dominated forests were primarily driven by mixed-severity disturbance regimes, with windstorms as the main disturbance agent. ii) Low- and moderate-severity disturbances prevailed, but the occurrence of plot-level high- and very-high severity disturbances were also documented. Disturbances affected several plots simultaneously over short periods, thus creating a coarse-grained forest structure. iii) We found significantly higher synchronicity of disturbances within the forests of the Western Carpathians compared to the Eastern Carpathians, where tree species richness is higher than in the Eastern Carpathians. No significant differences in patch sizes were detected between the Western and Eastern Carpathians. The size of patches was more heterogeneous in the East than in the West. iv) We found significantly higher synchronicity of disturbances in forests where the species composition was richer, with the suggestion that the mixture of spruces as a gapmaker had a significant effect on the disturbance pattern. Moreover, the GLM of the species composition

Abstract:

– disturbance synchronicity relation showed a strong dependence of synchronicity on the number of tree species per stand. The results contradict the general assumption that mixed forests have higher resilience, because of the significant mixture of spruces.

Keywords

Natural disturbances, Primary forest, Species composition, Synchronization, Dendroecology, Disturbance regime, Beech-dominated forest, Natural dynamics

Language used: English

Date on which the thesis was submitted / produced: 14. 2. 2024

Thesis defence

• Supervisor: prof. Ing. Miroslav Svoboda, Ph.D.
• Reader: Václav Treml, externi, Jan Tumajer, Ing., externi, Ivana Vašíčková, externi

Czech University of Life Sciences Prague

Faculty of Forestry and Wood Sciences

Doctoral programme / field:
Forestry Engineering / Forest Biology