What was done
The authors estimated the living above-ground biomass (AGB) and its turnover in a 50-hectare plot of moist tropical forest on Barro Colorado Island (BCI), Panama, using inventory data collected every five years from 1985 to 2000.

What was learned
Including branchfalls, AGB changes during the three intervals were determined to be: 1985-1990 (+0.82 ± 0.84 Mg ha^-1 year^-1), 1990-1995 (-0.69 ± 0.82 Mg ha^-1 year^-1), and 1995-2000 (+0.45 ± 0.70 Mg ha^-1 year^-1), for a 15-year average of +0.20 Mg ha^-1 year^-1, but with a confidence interval that spanned zero (-0.68 to 0.63 Mg ha^-1 year^-1)

What it means
The authors say they "have addressed another line of evidence [in addition to inverse modeling results (Rayner et al., 1999; Bousquet et al., 2000; Malhi and Grace, 2000; Gurney et al., 2002)] in favour of a tropical sink of atmospheric carbon: the evidence of an AGB sink from forest inventories (Phillips et al., 1998)."  However, they caution that "the sampling uncertainty (not to mention the measurement uncertainty) is much greater than the size of the sink itself."  Hence, they say they "cannot reject the hypothesis that the above-ground portion of the BCI forest is in carbon balance with the atmosphere."

References
Bousquet, P., Peylin, P., Ciais, P., Le Quere, C., Friedlingstein, P. and Tans, P.P.  2000.  Regional changes in carbon dioxide fluxes of land and oceans since 1980.  Science 290: 1342-1346.

Gurney, K.R., Law, R.M., Denning, A.S., Rayner, P.J., Baker, D., Bousquet, P., Bruhwiler, L., Chen, Y.-H., Ciais, P., Fan, S., Fung, I.Y., Gloor, M., Heimann, M., Higuchi, K., John, J., Maki, T., Maksyutov, S., Masarie, K., Peylin, P., Prather, M., Pak, B.C., Randerson, J., Sarmiento, J., Taguchi, S., Takahashi, T. and Yuen, C.-W.  2002.  Towards robust regional estimates of CO2 sources and sinks using atmospheric transport models.  Nature 415: 626-630.

Malhi, Y. and Grace, J.  2000.  Tropical forests and atmospheric carbon dioxide.  Trends in Ecology and Evolution 15: 332-337.

Phillips, O.L., Malhi, Y., Higuchi, N., Laurance, W.F., Nuñez, P.V., Vasquez, R.M., Laurance, S.G., Ferreira, L.V., Stern, M., Brown, S. and Grace, J.  1998.  Changes in the carbon balance of tropical forest: evidence from long-term plots.  Science 282: 439-442.

Rayner, P.J., Enting, I.G., Francey, F.J. and Langenfelds, R.  1999.  Reconstructing the carbon cycle from atmospheric CO2, ¹³C and O2/N2 observations.  Tellus B 51: 213-232.