Biomass and growth potential of Eucalyptus regnans up to 100 m tall
Predicting tree biomass and growth increments via allometric equations is routine in forestry, but this approach is problematic in old-growth forests unless equations are derived from trees spanning the full size range. Using intensive measurements of 27 standing Eucalyptus regnans trees 61.1–99.8 m tall and 80–430 years old in Tasmania, Victoria, and New Zealand, we develop allometric equations to predict aboveground attributes, including biomass and annual growth increments, of trees >60 m tall using ground-based measurements. Power functions of diameter underestimate biomass growth increments unless measurements are made above buttressing on the lower trunk. Growth anomalies apparent in several trees suggest that wounded E. regnansexpend considerable energy to outgrow decay fungi and prevent structural collapse. Despite declining growth efficiency – defined as biomass growth per unit mass of photosynthetic tissues – with increasing tree size and age, biomass growth increments of E. regnans increase as trees enlarge with age until extrinsic forces cause mortality. The largest living E. regnans has an aboveground biomass of 215 Mg and a growth increment of 0.784 Mg year−1, not accounting for mass loss due to decay. An even larger E. regnanstree – killed by fire in 2003 – had an aboveground biomass of ∼270 Mg, an estimated growth increment of ∼1 Mg year−1, and was ∼480 years old at the end of its life. Prior to a stand-replacing fire in 2009, Australia’s tallest forest had a maximum aboveground biomass of 1504 Mg ha−1 and a maximum aboveground carbon mass of 706 Mg ha−1.