The effects of phytophagous insects on water and soil nutrient concentrations and fluxes through forest stands of the Level II monitoring network in the UK

The effects of insect defoliators on throughfall and soil nutrient fluxes were studied in coniferous and deciduous stands at five UK intensive monitoring plots (1998 to 2008) Links were found between the dissolved organic carbon (DOC) nitrogen (N) and potassium (K) fluxes through the forest system to biological activity within the canopy Underlying soil type determined the leaching or accumulation of these elements Under oak monitored at two sites frass from caterpillars of Tortrix viridana and Operophtera brumata added direct deposition of -16 kg ha(-1) extra N during defoliation Peaks of nitrate (NO3-N) flux between 5 and 9 kg ha(-1) (x5 usual winter values) were recorded in consecutive years in shallow soil waters Synchronous rises in deep soil NO3-N fluxes at the Grizedale sandy site indicate downward flushing not seen at the clay site Under three Sitka spruce stands generation of honeydew (DOC) was attributed to two aphid species (Elatobium abietinum and Clara pilicornis) with distinctive feeding strategies Throughfall DOC showed mean annual fluxes (6 seasons) similar to 45-60 kg ha(-1) compared with rainfall values of 14-22 kg ha(-1) Increases of total N in throughfall and NO3-N fluxes in shallow soil solution were detected soil water fluxes reached 8 kg ha(-1) in Llyn Brianne similar to 25 kg ha(-1) in Tummel and similar to 40 kg NO3-N ha(-1) in Coalburn At Tummel on sandy soil NO3-N leaching showed increased concentration at depth attributed to microbiological activity within the soil By contrast at Coalburn and Llyn Brianne sites on peaty gleys soil water NO3-N was retained mostly within the humus layer Soil type is thus key to predicting N movement and retention patterns These long term analyses show important direct and indirect effects of phytophagous insects in forest ecosystems on above and below ground processes affecting tree growth soil condition vegetation and water quality Crown Copyright (C) 2010 Published by Elsevier B V All rights reserved