Tree Harvest in an Experimental Sand Ecosystem Pl

Authors: C K Keller R O’Brien J R Havig J L Smith B T Bormann D Wang

Publish Date: 2006/05/31

Volume: 9, Issue: 4, Pages: 634-646

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Abstract

The hydrochemical signatures of forested ecosystems are known to be determined by a timevariant combination of physicalhydrologic geochemical and biologic processes We studied subsurface potassium K calcium Ca and nitrate NO3 in an experimental red pine mesocosm to determine how trees affect the behavior of these nutrients in soil water both during growth and after a harvest disturbance Solution chemistry was monitored for 2 years at the end of a 15year period of tree growth and then for 3 more years after harvest and removal of aboveground biomass Concentrations were characterized by three distinct temporal patterns that we ascribe to changes in solute generation mechanisms Prior to harvest K soilwater concentrations were relatively uniform with depth whereas Ca soilwater concentrations doubled with depth Nitrate concentrations were below detection in soil water and discharge drainage water Plant uptake and water/nutrient cycling exerted strong control during this interval During the 1st year after harvest K concentrations tripled in shallow soil water relative to preharvest levels and showed a strong seasonal peak in discharge that mimicked soil temperature Summer soil temperatures and annual water flux also increased Decomposition of labile litter with complete nitrogen N immobilization characterized this interval In the third interval years 2 and 3 after harvest decomposition shifted from N to carbon C limitation and Ca and NO3 concentrations in discharge spiked to nearly 200 and 400 μM respectively Relatively stable ionic strength and carbonate chemistry in discharge throughout the study period indicate that carbonicacid weathering was sustained by belowground decomposition long after the harvest This stable chemical weathering regime along with the persistence of N limitation for a long period after disturbance may be characteristic of earlyphase primarysuccessional systemsThis work was supported by National Science Foundation grants EAR9628296 and EAR0312011 to C K Keller We also acknowledge financial and logistical support by the Hubbard Brook Experimental Forest and the Pacific Northwest Research Station of the USDA Forest Service the Rubenstein School of Environment and Natural Resources at the University of Vermont and the departments of Geology and Crop and Soil Sciences at Washington State University G Hawley and F H Bormann provided encouragement help with data collection and constructive comment T Coe provided invaluable analytical and data management assistance We thank G Likens and R Berner for sharing data and T White V Levasseur B Dresser J Tabolt K Reinhardt and C Johnson for field assistance This is a contribution of the Hubbard Brook Ecosystem Study and the program of the Institute of Ecosystem Studies

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