Temporal fluctuations in throughfall carbon concentrations in a spruce forest

Fluxes of nutrients, energy and ions through forest canopies are spatially and temporally highly heterogeneous and good modelling tools are needed to separate different influential variables. Two important factors affecting the variation in the throughfall fluxes are the amount of precipitation and phytophagous insects in the canopy. In spite of their large abundance, wide distribution and production of large quantities of sugary excreta the role of aphids has not been explored in models of DOC-flux dynamics. We hypothesise that aphids qualify as a crucial factor to better explain the spatial and temporal variability in DOC-fluxes. Here, we build on the available knowledge of aphid population dynamics to explore the relative roles of aphids and precipitation as sources of variability in throughfall fluxes in a mature spruce forest. Peaks in DOC-concentrations usually appeared during June-August and precipitation volumes alone were insufficient to explain DOC-concentrations in throughfall. The developed dynamical model, however, showed a 34% increase in the explained variability in DOC throughfall dynamics if aphids were included. This is the first model, which takes into account the possible influence of sap feeding herbivores on DOC-flux dynamics. (C) 2004 Elsevier B.V. All rights reserved.