Reducing uncertainty in the use of allometric biomass equations for predicting above-ground tree biomass in mixed secondary forests

Estimates of forest biomass are needed for tracking changes in C stocks, as well as for other purposes. A common method for estimating forest biomass is through use of allometric equations which relate the biomass of individual trees to easily obtainable non-destructive measurements, such as diameter. A common form is B=aD(b) for biomass B, diameter D and parameters a and b. Field data collected in Sumatra and compared with previously published data show that the values of a and b vary between sites. This variation is likely to be the major source of uncertainty if biomass estimates are produced using equations that are not calibrated for individual sites. However, calibration by collection of B and D data for each site is unrealistic, requiring destructive measures. Methods of choosing values for a and b are, therefore, proposed that do not require destructive measurements. The parameter b can be estimated from the site-specific relationship between height (H) and diameter, H=kD(c) as b=2+c. The parameter a can be estimated from the average wood density (rho) at the site as a=r rho, where r is expected to be relatively stable across sites. The allometric equation proposed is therefore B=r rhoD(2+c). (C) 2001 Elsevier Science B.V. All rights reserved.