Comparing above-ground biomass among forest types in the Wet Tropics: small stems and plantation types matter in carbon accounting

Revenue from carbon credits from rainforest stands could encourage reforestation for biodiversity conservation on private land in north-eastern Queensland, Australia. Current models and allometrics for estimating carbon, however, are not calibrated against sites in the region and underestimate carbon stocks. We assess the accuracy of the two accepted methods to estimate carbon stocks in Australian rainforests: FullCAM and the Keith et al. (2000) allometric. We also assess the effect of FullCAM's discounting of small stems (2.5–10 cm) to carbon stocks, and compare the carbon benefits of the three reforestation methods in the region to identify planting configurations with the best carbon sequestration potential. We sampled 27 rainforest stands in north-eastern Queensland. Using these data we calculated above-ground biomass (AGB) using the Keith allometric and derived the above-ground carbon (AGC). We compared our estimates across three reforestation methods with the FullCAM modelled estimates for the same sites, and with estimates derived from two global rainforest allometrics (Brown, 1997 and [Chave et al., 2005]). The Keith allometric estimated that planted forests yielded on average 20 Mg of tradable carbon ha−1 y−1 (i.e. CO2-equivalent), with no differences between plantation forests and environmental plantings, although the former had more large diameter stems. Small stems (<10 cm) accounted for 15.1% of AGB in plantings