RA3 Thesis: Assessing kauri stands with Laser ...

Cordes M. 2023. Assessment of Forest Structural Complexity in Kauri (Agathis australis) Dominated Stands affected by Kauri Dieback using Mobile Terrestrial Laser Scanning. Unpublished Masters thesis, Georg-August-University Göttingen.

This thesis is not publicly available online. For further information please contact supervisor, Dr. Luitgard Schwendenmann at the University of Auckland

Forest development is determined by various biotic and abiotic factors over time, resulting in distinctive spatial patterns of vegetation. Forest Structural Complexity (FSC) metrics, derived from laser-scanning-generated point clouds, are increasingly used to analyse these patterns and to describe and investigate related ecosystem functions, such as light availability. Furthermore, FSC is influenced by species composition, their traits, and potential complementarity effects in tree canopy architecture and is expected to show recognisable variations by different disturbance agents. The endemic tree species of New Zealand, kauri (Agathis australis), faces a significant threat from the soil-borne pathogen Phytophthora agathidicida. This pathogen affects the water and nutrient transport of the keystone species, leading to the lethal disease known as kauri dieback. This study aimed to assess the current structural complexity of 6 long-term monitoring plots of a kauri-dominated forest ecosystem in northern New Zealand and to develop a standardised method to investigate the effects of P. agathidicida on kauri demography by mobile terrestrial laser scanning. A set of 16 structural metrics, across four distinct dimensional foci, were selected to investigate a variety of structural characteristic groups. Furthermore, a progressive symptomatic defoliation simulation was performed to identify the most suitable metrics of this approach for following research. The FSC metrics indicate distinct variations between old growth and secondary forest plots, with greater consistency and structural complexity observed within old growth forest plots in contrast to more pronounced differences among secondary forest plots. Besides basic statistical measures, arrangement and heterogeneity metrics are promising to detect changes in FSC. Nevertheless, the non-uniform distribution of laser points, typically for the used scanning system, leads to bias sources for individual structural metrics. The findings of this thesis create the baseline for following research on structural change of kauri-dominated ecosystems and contribute to the development of a comprehensive understanding of the effects of P. agathidicida.