Table 1. Inputs and sources of uncertainty in estimates of forest carbon stock, as well as methods applied to reduce these uncertainties.

Input Source of uncertainty Method to reduce uncertainty
Selection of forest plots Sampling error Forest plot geo-coordinates were selected using random number generation, within logistical constraints, and good practice for sampling design and forestry inventory was followed (MacDicken 1997, Pearson et al. 2005, Greenhalgh et al. 2006, Grassi et al. 2008).
 
Measurement of diameter at breast height (dbh) Measurement error Training and education in measurement of dbh was conducted to reduce measurement error. It was ensured that trees were not measured twice or dead trees counted as living. Measurement uncertainty on a single tree of diameter 10 cm or greater has been estimated at 16% but found to average out at forest stand level (Chave et al. 2004).
 
Application of allometric equation Estimation error:
allometric equations originating from Asian and Latin American data
Pan-tropical equations are based on a large number of trees from Asia and Latin America spanning a range of diameters. Because destructive sampling of trees to create an area-specific allometric regression equation was not possible, the application of pan-tropical allometric equations was appropriate within dbh values used to create the regression equations. Error attributable to the allometric equation is estimated at 10–20% (Clark and Clark 2000, Keller et al. 2001, Ketterings et al. 2001, Chave et al. 2004).
 
Application biomass to carbon ratio Estimation error:
the carbon density of biomass components and tree species differ
The IPCC 2006 present a default value of 0.47 for tropical and subtropical forest but within an interval estimate of 0.44–0.49. This is an improvement on 0.5 suggested by Westlake (1966), but suggests a relative error of 5%.