Biomass distribution and above- and below-ground production in young and mature Abiesamabilis zone ecosystems of the Washington Cascades

Abstract

Biomass distribution and above- and below-ground net primary production were determined for 23- and 180-year-old Abiesamabilis (Dougl.) Forbes ecosystems growing at 1200-m elevation in the western Washington Cascade Range. Total organic matter accumulations were 427.0 t•ha⁻¹ in the young stand, and 1247.1 t•ha⁻¹ in the mature stand. Aboveground tree and detritus biomass were 49.0 t•ha⁻¹ and 130.2 t•ha⁻¹, respectively, in the young stand compared with 445.5 t•ha⁻¹ and 389.4 t•ha⁻¹ in the mature stand. Net primary production (NPP) was 18.3 t•ha⁻¹ in the young stand and 16.8 t•ha⁻¹ in the mature stand. Belowground dry matter production was 65% of total net production in the young stand and 73% of total net production in the mature stand. Conifer fine root production was 35.9% of NPP in the young and 66.4% of NPP in the mature stand. This apparent shift in fine root production as a proportion of NPP may be related to detritus accumulation.