title: Drivers of decomposition in the tropics: effects of climate and land-use on soil invertebrates
Creators: name: Röder, Juliane
Publisher: name: Philipps-Universität Marburg
Year: 2024
Subjects: Streuabbau
Wirbellose
Ökologie
Höhengradient
Landnutzung
Klima
Zersetzung
Natural sciences &amp; mathematics
Naturwissenschaften

description: The decomposition of plant material is an essential part of carbon cycling, and climate and invertebrates are two major drivers controlling decomposition rates. In tropical forests, carbon stocks and carbon turnover are high, but large-scale land-use change continues to reduce carbon stocks and ecosystem functioning. Tropical mountain forests are especially vulnerable to climate and land-use change, thus they are also good places to study these changes and their interactions. Here, combined effects of climate and land-use change could have diverging effects on direct and indirect drivers of decomposition, with negative consequences for ecosystem functioning. In this context, the abundance and activity of soil arthropods are important for decomposition rates, but not necessarily responding to the same abiotic and biotic conditions in a similar manner. In this thesis, I studied separate and interactive effects of climate, land-use and productivity on the abundance of arthropod decomposers and other taxa and feeding guilds, on decomposition rates, and on soil fauna activity in tropical mountain ecosystems.
Ecological processes are driven by the number and the biomass of individuals. Understanding the variations in animal abundance is therefore important for predicting changes in ecosystem processes under global warming and land-use change. In the second chapter, I tested the relative importance of temperature, humidity, plant productivity and disturbance for the abundances of 13 focal taxa of epigeic invertebrates, and for the functional groups of predators, herbivores and decomposers, respectively. I could show that taxa belonging to the same functional group did not show more similar responses to elevation than taxa from different functional groups. Furthermore, temperature, not primary productivity, was the single most important factor predicting the abundance of all taxa combined. Most of the taxa showed unimodal patterns with a peak in activity abundance in lower montane forests, indicating that humidity was limiting the occurrence of desiccation sensitive arthropods in savanna and maize fields.
Deforestation and land-use change in tropical forests often decrease decomposition rates, but studies are often limited to a small range of climatic conditions. Thus, in my third chapter, I studied how aboveground litter decomposition responded to temperature, humidity, land-use intensity, and interactions of climate and land-use. I could show that climate was the major driver of decomposition in this study. Further, effects of disturbance were dependent on the subset of analysed vegetation types and on the season. High land-use intensity resulted in lower decomposition rates, but only in the warm wet season, when decomposition rates were overall lower than in the cold wet season.
Soil invertebrates are key drivers of decomposition and carbon cycling. Therefore, in my fourth chapter, I studied how soil fauna activity responded to temperature, humidity, land-use intensity, and interactions of climate and land-use. I found soil fauna activity was sensitive to humidity, while temperature was not as important as expected. In disturbed vegetation types, soil fauna activity was consistently higher than in natural vegetation types. Furthermore, soil fauna activity was highly seasonal in savanna and maize fields.
Overall, I could show that patterns of arthropod abundance along the elevation gradient depended on the level of taxonomic and functional resolution. This highlights the need for multi-taxon approaches for predictions of functional groups and related ecosystem functions. Furthermore, I found that climate was the most important driver of decomposition. I also found that vegetation types with moderate levels of disturbance can retain high functionality regarding carbon cycling. Finally, I could show that the effects of land-use intensity on soil fauna activity were modulated by climate, and that more arid vegetation types were more sensitive to seasonal variation.