Quantifying the impact of forest management intensity and tree species diversity on individual tree shape and three-dimensional stand structure
von Julia Juchheim
Datum der mündl. Prüfung:2020-09-18
Erschienen:2020-11-04
Betreuer:Prof. Dr. Christian Ammer
Gutachter:Prof. Dr. Christian Ammer
Gutachter:Prof. Dr. Dirk Hölscher
Dateien
Name:eDiss_Julia_Juchheim.pdf
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Zusammenfassung
Englisch
The three-dimensional distribution of trees and their crowns is an essential characteristic of forest ecosystems that is directly related to several ecosystem functions and services. Silvicultural interventions modify the stand structure and thus have a major impact on the ecological and economical value of a forest stand. In the past, it was challenging to obtain quantitative data on the effects of different silvicultural treatments on tree architecture and three-dimensional stand structure. Comprehensive manual measurements of crown characteristics in mature stands were labor-intensive, time-consuming and, because of the complexity of the canopy, difficult to realize on a large-scale. In recent years, terrestrial laser scanning (TLS) allowed great advances in measuring the three-dimensional forest structure with reasonable effort and high accuracy. Terrestrial laser scanning is a ground-based active remote sensing technique that measures the distance between a laser scanner device and an object by transmitting laser energy. The distance to the target is calculated either by the phase difference between the transmitted and the received laser light or by the laser return time. Spatial data on the scanned objects is then available in form of three-dimensional point clouds. In the present work, we used terrestrial laser scanning data to quantify the impact of forest management intensity and tree species diversity on individual tree shape and three-dimensional stand structure. We conducted our studies within the framework of the Biodiversity Exploratories, a long-dated and large-scaled project which addresses the relationship between land-use intensity and biodiversity. The research plots are located in three different regions of Germany: the Swabian Alb in southwest Germany, the Hainich-Dün in central Germany, and the Schorfheide-Chorin in northeast Germany. In our first study we identified that structural attributes of European beech trees, such as crown and trunk shape or branching patterns, were significantly influenced by silvicultural management intensity and stand composition. Our findings demonstrate the high plasticity of beech and indicate an increasing competition with decreasing management intensity and a higher competitive pressure for beech trees growing in pure stands than for beech trees surrounded by valuable hardwoods. Our second study showed that an increasing management intensity in beech stands led to a vertically more even distribution of aboveground biomass. The regularly thinned stands showed a higher canopy space filling compared to the unmanaged stands, despite the removal of trees. In addition, our results revealed that a higher space filling, particularly in the shaded canopy, positively affected stand productivity. In our third study we could show that an increasing tree species diversity enhanced the complexity of the stand structure. Furthermore, we found that an increasing share of broadleaved trees increased the structural complexity of coniferous stands. The presented results contribute to a better understanding of how different management approaches modify tree and stand structure and provide insights to promote certain ecosystem functions and services of forests.
Keywords: Fagus sylvatica; tree species diversity; three-dimensional stand structure; forest management intensity; terrestrial laser scanning; tree shape