Pre-logging carbon accounts in old-growth forests, via allometry: An example of mixed-forest in Tasmania, Australia

Uncertainty in past and future anthropogenic carbon emissions obscures climate change modelling. Available allometrics are insufficient for regional-level accounting of old-growth, pre-logging carbon stocks. The project goal was to determine the aboveground carbon (biomass and necromass) for a typical old-growth Eucalyptus delegatensis-dominated mixed-forest in Tasmania. Allometrics were developed for aboveground biomass of Eucalyptus delegatensis and generic rainforest understorey species. A total of 207 eucalypts with DBH 0.21-4.5 m, and 897 rainforest understorey trees with DBH 0.01-2.52 m were measured across 7.7 ha. DBH frequency distribution of E. delegatensis showed at least two age cohorts and distinct positive skew, whereas its DBH carbon distribution showed distinct negative skew. Half of the eucalypt biomass was from trees with DBH > 2.4(0.1) m, and 16% with DBH ≥ 3.5 m (from ∼1.1 trees ha⁻¹) – indicating the importance of allometrics for high DBH. Aboveground carbon was 622(180) Mg ha⁻¹, with ∼20% from understorey and ∼25% from necromass. The carbon in aboveground biomass was above the median value for temperate forests. The long-term aboveground-carbon emissions from clearfelling the same forest type from 1999 to 2009 is likely to be 2.9(±1.3) Tg, depending on the growth and seral stages of the forest logged.