Allometric equations for Sequoia sempervirens in forests of different ages

•New allometric equations for Sequoia sempervirens in second-growth forest.•Evaluation of bias in allometric equations derived from forests of different ages.•Complete structural analysis of 159-year-old forest in Fritz Wonder Plot.•Estimating aboveground biomass and carbon stock in mature and old-growth forests.•Comparison of long-term tree performance and canopy structure in alluvial forests.