An Investigation into Decaying Kauri Fine Woody Debris: The Invertebrates and Properties Associated with Different Stages of Decomposition

Abstract

Dead wood is known for the important role it plays in nutrient cycling and habitat provision in a forest ecosystem. Termed ‘woody debris’, this wood is broken down and decomposed by organisms such as invertebrates. The considerable influence woody debris has over saproxylic invertebrate community composition is related to the chemical constituents and physical properties of the wood, as well as the surrounding environmental conditions. This thesis examined the invertebrate communities associated with kauri fine woody debris (FWD, < 5 cm in branch diameter), the environmental factors that influence invertebrate community composition, and the physical properties and chemical constituents of kauri FWD for each stage of decomposition. Wet weights of branches were recorded and invertebrates were extracted from kauri FWD from each stage of decomposition. Intermediately decomposed (stage 2) invertebrate communities were further analysed against environmental factors including dry weight, distance to nearest tree, density, basal area, air and soil temperature and soil moisture. Physical properties (wet and dry weight, moisture, saturation and density) and chemical constituents (pH and concentrations of C, N, P, K, Mg and Ca) were analysed for each stage of decay, and against the invertebrate communities of stage 2 woody debris. A total of 22 invertebrate phyla were associated with kauri FWD. Significantly more material was observed in the later two stages of decomposition, with an increase in invertebrate abundance and ordinal diversity also observed in these stages. Wood dry weight was found to have the strongest environmental influence on the invertebrate communities, highlighting different invertebrate functional groups (decomposers and predators). Physical and chemical characteristics differed between stage 1 and the later two stages of decomposition. This study provided the first comprehensive insight into kauri FWD and its saproxylic invertebrate communities in a Phytophthora taxon Agathis (PTA)-free kauri stand. Kauri mortality due to PTA is likely to increase dead wood quantities. This will result in cascading community effects, and highlights the importance of knowing what is associated with kauri dead wood ecosystems. Thus, research should be extended to PTA-affected kauri stands and further research is recommended to fully understand the successive changes in kauri FWD decomposition.