Impacts and drivers of insect herbivory on element cycling in forests globally

• Main Author: Hwang, Bernice
• Format: Doctoral or Postdoctoral Thesis
• Language: English
• Published: Lund University 2022
• Subjects: Ecology; biogeochemical cycling; folivory; insect cadavers; insect frass; insect herbivory; litter decomposition; nutrient cycling; carbon; nitrogen; phosphorus; silicon; silica; Antarc*; Antarctica
• Online Access: https://lup.lub.lu.se/record/503cf455-3be9-46ce-bf76-71c567ec701c; https://portal.research.lu.se/files/125624401/ThesisAbstract.pdf

The effects of insect herbivores on forest functioning are not well understood even though they can have important impacts on ecosystem processes by intercepting foliage before resorption and depositing nutrient-rich materials to the soil. In this thesis, I investigated the impact and drivers of insect folivores on carbon (C), nitrogen (N), phosphorus (P) and silica (Si) cycling in broadleaf forests, and how this varies with major climate variables. I first synthesized existing literature to identify gaps in knowledge and prioritize future research about the plant-silica-herbivore relationship, which has been overlooked despite recent growing interest in the importance of silica in terrestrial systems. In the field, I led the establishment of a network collecting leaf litter, fresh leaves, and soil from 74 plots in 40 broadleaf primary forests distributed across all continents (except Antarctica) using standardized methods to measure foliar production and background leaf-level herbivory rates. From these data, I calculated insect-mediated element fluxes from the canopy to the soil and compared them to other major sources of these nutrients. To learn how major climate variables may influence these fluxes locally and globally, a subset of plots was established along nine natural temperature and three precipitation gradients. Finally, I investigated how temperature can affect the movement of C and N in locally sourced leaf litter and three levels of insect frass + cadaver amendments decomposing along a highly constrained elevation gradient, to provide insights into the cascading effects of these deposits on decomposition processes.I found substantial evidence for a wide variety of important interactions between plant Si and herbivory but highlight the need for more research particularly in non-graminoid-dominated vegetation outside of the temperate biome as well as on the potential effects of herbivory on Si cycling. The global mean for net insect-mediated N flux was approximately 25% of the global mean for ...