HR: 14:40h
AN: B33F-05    [Abstracts]
TI: The Effects of Disturbance and Nitrogen Deposition on Carbon Uptake by Boreal and Temperate Forests
AU: * Law, B
EM: bev.law@oregonstate.edu
AF: Oregon State University, Richardson Hall, Corvallis, OR 97331, United States
AU: Magnani, F
EM: federico.magnani@unibo.it
AF: University of Bologna, Department of Fruit Tree and Woody Plant Science, Bologna, I- 40127, Italy
AU: Mencuccini, M
EM: m.mencuccini@ed.ac.uk
AF: University of Edinburgh, School of GeoSciences, Edinburgh, EH93JU, United Kingdom
AU: Borghetti, M
EM: marco.borghetti@unibas.it
AF: University of Basilicata, 3Department of Crop Systems, Forestry and Environmental Sciences, Potenza, 85100, Italy
AU: Luyssaert, S
EM: sebastiaan.luyssaert@oregonstate.edu
AF: Oregon State University, Richardson Hall, Corvallis, OR 97331, United States
AU: Luyssaert, S
EM: sebastiaan.luyssaert@oregonstate.edu
AF: University of Antwerp, Universiteitsplein 1, Wilrijk, 2610, Belgium
AU: Grace, J
EM: jgrace@ed.ac.uk
AF: University of Edinburgh, School of GeoSciences, Edinburgh, EH93JU, United Kingdom
AB: Fourteen chronosequences (83 sites) in temperate and boreal forests were used to examine the effects of disturbance and nitrogen deposition on net carbon uptake. Because effects of disturbance, temperature, and nitrogen deposition are difficult to disentangle, process-based and empirical models were used to interpolate measurements between ages to estimate C fluxes at every age in the rotation and obtain averages without risks associated with a limited sample size. The temporal dynamics following stand-replacing disturbances account for a very large fraction of the overall variability in forest carbon sequestration. Data from the 14 chronosequences of individual stands showed that annual NEP was only poorly correlated with wet N deposition at the stands (R2 = 0.16) as a result of the predominant effect of age on C fluxes. This was in contrast with the very good correlation observed with rotation-averaged NEP (NEPav) for the same chronosequences (R2 = 0.92). Time since disturbance explained 70% of the total variability in the dataset. After the confounding effects of disturbance were factored out, NEPav appeared to be driven by wet nitrogen deposition. No signs of N saturation were apparent in our data set, which explored a broad range of wet deposition up to 9.8 kgN/ha/yr (15 kgN/ha/yr of total N deposition), representing more than 90% of Western Europe and the conterminous United States. Preliminary analysis of data from over 100 sites was conducted to understand the mechanisms responsible for the increase in NEP. We found that N deposition stimulated GPP and woody biomass production proportionally, while a large amount of carbon was used for production of short-lived tissues. Yet, N deposition appeared to reduce heterotrophic respiration and associated carbon losses from soil. Modeling considerations include C:N coupling and changes in processes with time since disturbance.
DE: 0400 BIOGEOSCIENCES
DE: 0414 Biogeochemical cycles, processes, and modeling (0412, 0793, 1615, 4805, 4912)
DE: 0428 Carbon cycling (4806)
SC: Biogeosciences [B]
MN: 2007 Fall Meeting