Biomass, production and woody detritus in an old coast redwood (Sequoia sempervirens) forest

Abstract

We examined aboveground biomass dynamics, aboveground net primary production (ANPP), and woody detritus input in an old Sequoia sempervirens stand over a three-decade period. Our estimates of aboveground biomass ranged from 3300 to 5800 Mg ha⁻¹. Stem biomass estimates ranged from 3000 to 5200 Mg ha⁻¹. Stem biomass declined 7% over the study interval. Biomass dynamics were patchy, with marked declines in recent tree-fall patches <0.05 ha in size. Larger tree-fall patches approaching 0.2 ha in size were observed outside the study plot. Our estimates of ANPP ranged from 6 to 14 Mg ha⁻¹yr⁻¹. Estimates of 7 to 10 Mg ha⁻¹yr⁻¹ were considered to be relatively accurate. Thus, our estimates based on long-term data corroborated the findings of earlier short-term studies. ANPP of old, pure stands of Sequoia was not above average for temperate forests. Even though production was potentially high on a per stem basis, it was moderate at the stand level. We obtained values of 797 m³ ha⁻¹ and 262 Mg ha⁻¹ for coarse woody detritus volume and mass, respectively. Fine woody detritus volume and mass were estimated at 16 m³ ha⁻¹ and 5 Mg ha⁻¹, respectively. Standing dead trees (or snags) comprised 7% of the total coarse detritus volume and 8% of the total mass. Coarse detritus input averaged 5.7 to 6.9 Mg ha⁻¹yr⁻¹. Assuming steady-state input and pool of coarse detritus, we obtained a decay rate constant of 0.022 to 0.026. The old-growth stand of Sequoia studied had extremely high biomass, but ANPP was moderate and the amount of woody detritus was not exceptionally large. Biomass accretion and loss were not rapid in this stand partly because of the slow population dynamics and low canopy turnover rate of Sequoia at the old-growth stage. Nomenclature: Hickman (1993).