4.4.1 Structural change Among 123 long-term old-growth Amazonian plots with full tree-by-tree data, there was a significant increase in aboveground biomass between the first measurement(late twentieth century, median date 1991) and the last measurement before the 2005 drought(median date 2003).
For trees 210 cm diameter the increase has been 0.45(0.33, 0.56) tonnes of carbon per hectare per year(mean, 2.5% and 97.5% confidence limits: Phillips et al. 2009). Across all 123 Amazon plots, the aboveground biomass change is approximately normally distributed and shifted to the right of zero(Figure 4.3A).
The overall net increase estimated is slightly lowerthan but statistically indistinguishable from the 0.54 0.29 tC ha yr estimated by Phillips et al. (1998) for the lowland Neotropics using 50 sites up to 1996, and the Baker et al. (2004a) estimate of 0.62 t 0.23 tC ha yr 1 for 59 core RAINFOR Amazon plots up 2000.
In the larger dataset that is now available, estimates of biomass carbon change always give a positive carbon uptake and are also rather.