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CD-08 Abstract

Carbon Dynamics in Vegetation and Soils Along the Eastern LBA Transect

Plínio Barbosa de Camargo — USP - Universidade de Sao Paulo (SA-PI)
Susan E. Trumbore — University of California (US-PI)

Our overall goals are to

quantify the contributions of different components of the carbon cycle to

overall ecosystem carbon balance in Amazonian tropical forests and to undertake

process studies at a number of sites along the eastern LBA transect to

understand how and why these fluxes vary with site, season, and year. We are

dividing this work into a number of specific tasks: (1) determining the average

rate (and variability) of tree growth over the past 3 decades; (2) determining

age demographics of tree populations, using radiocarbon to determine tree age;

(3) assessing the rate of production and decomposition of dead wood debris; (4)

determining turnover rates for organic matter in soils and the mean age of C

respired from soil using radiocarbon measurements; and (5) comparing our results

with models and constructing models to predict the potential of tropical forests

to function as sources or sinks of C.

The overall

picture of tropical forest C dynamics emerging from our Phase I studies suggests

that the fraction of gross primary production allocated to growth in these

forests is only 25-30%, as opposed to the 50% assumed by many ecosystem models. 

Consequent slow tree growth rates mean greater mean tree age for a given

diameter, as reflected in our measurements and models of tree age. 

Radiocarbon measurements in leaf and root litter suggest that carbon stays in

living tree biomass for several years up to a decade before being added to

soils, where decomposition is rapid. The time lags predicted from 14C, when

coupled with climate variation on similar time scales, can lead to significant

interannual variation in net ecosystem C exchange.

In Phase II

we will continue our measurements to observe how forest C budgets can vary from

year to year with climate.  In addition to filling gaps in our stand-level

C budgets, activities we will (1) expand our efforts in integration across sites

through modeling, and (2) augment our existing measurements where needed to

facilitate modeling (through availability of continuous temperature and moisture

data), or to fill gaps in coverage of C cycle components, and (3) continue

measurements begun in the past year to study differences in C dynamics between

primary forest and other land cover types (flooded forest and cerrado). Some

more detailed physiological measurements begun by Chambers, Higuchi, Santos, and

Tribuzy at the INPA ZF2 forest and FLONA seca floresta project will continue in

Year 1.

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