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Materials and methods are available as supporting material on Science Online
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Materials and methods are available as supporting material on Science Online.
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0344869461
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note
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For the km 67 biometry study (27,49), we surveyed 20 ha of forest near the eddy-flux tower in July 1999 and resurveyed the same area in July 2001 (obtaining estimates of recruitment, growth, and mortality), including stocks of CWD. CWD respiration was calculated by applying density-specific respiration rates measured in the Amazon rainforest near Manaus to measured decay class-specific CWD mass at km 67 (27). Sampling uncertainty in all estimates was quantified using bootstrap analyses, with 95% Cls reported.
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The km 83 long-term biometry study (28, 49) compared a 1984 inventory of large trees (diameter at breast height > 55 cm) in 48 ha around the eddy-flux tower location with an inventory of the same area in 2000 to analyze the change in large tree biomass. The measured small tree:large tree biomass ratio was used to estimate changes in smaller trees. Errors were quantified using a sensitivity analysis that bracketed a highly conservative range of plausible uncertainty. Flux contributions resulting from a change in CWD stocks over the period, which were not measured in the km 83 study, are likely much less important than in the km 67 study because of the Long time between surveys (about twice the turnover time of CWD).
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2 stored in the canopy below the sensor).
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-1. We believe that the probability of the true balance falling outside of this range is very small, but it is not rigorously quantifiable (49).
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The Terrestrial Ecosystem Model (TEM) (4) is a highly aggregated box model. Results of model runs for the grid cell containing the towers are courtesy of J. Melillo and D. Kicklighter.
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0344437680
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The Integrated Biosphere Simulator (IBIS) (8) is a mechanistic dynamic vegetation model that simulates interactions among different plant functional types. The current version includes multiple soil layers. Results of model runs for the grid cell containing the towers are courtesy of J. Foley, M. Costa, and A. Botta.
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tot is greater than heterotrophic respiration by the amount of autotrophic respiration.
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0344006410
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Dry season decline in precipitation coincides with significant increases in other controlling variables at these sites, including photosynthetically active radiation, temperature, and vapor pressure deficit (VPD) (29), but the precipitation effect likely dominates; trends in VPD and photosynthetically active radiation have opposing effects on photosynthesis, whereas temperature increase would tend to increase dryseason respiration in the absence of water limitation.
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0344869456
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Mean number of months per year with <100 mm of rainfall (an indicator of dry-season intensity in tropical forests) was 4.7 (Tapajós), 2.4 (Manaus), and 2.8 months (Caxiuana) (13). The difference is stronger during the recent period of flux observations because the Manaus site experienced a wetter year and a wetter dry season than average during 1999 to 2000 (a La Nifia period) when the seasonality there was strongest (41), whereas the Tapajós experienced close to average precipitation during the 2000 to 2003 measurements reported here. Though the Tapajós is somewhat drier than these other eddy flux sites, it does not represent the dry extreme [25 to 30% of the forested Amazon basin experiences equally dry or drier conditions (49) (fig. S2)].
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49
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0345300766
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Materials and methods are available as supporting material on Science Online
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Materials and methods are available as supporting material on Science Online.
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-1) (table S1A) is at the 90th percentile of uptake observed across all 68 tropical forest plots in (12).
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Observed recruitment is high; long-term average recruitment rates in Amazonian permanent study plots were 0.8 to 2.8% (56).
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This paper is a product of the Large-Scale Biosphere-Atmosphere Experiment in Amazonia (LBA), led by Brazil's Ministry of Science and Technology. Supported by NASA grants (LBA-ECO) to Harvard University (NCC5-341) and University of California, Irvine (NCC5-280); the Conselho Nacional de Desenvolvimento Cientifico; and the Harvard College Research Program. We thank D. Fitzjarrald, J. Foley, D. Kicklighter, J. Melillo, and A. Nobre for helpful comments and discussion; V. Y. Chow for analysis of precipitation data; B. Reed, L. Merry, D. Hodkinson, F. A. Leão, D. Amaral, and the staff of the LBA-Santarém Office for their extensive logistical support and patience; and N. de Souza Carvalho, E. Pedroso, and N. Rosa for botanical identifications.
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