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

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Abstract
Biomass distribution and above- and below-ground net primary production were determined for 23 and 180 yr old A. amabilis (Dougl.) Forbes ecosystems growing at 1200 m elevation in the western Washington Cascade Range. Total organic matter accumulations were 427.0 t [ton] .cntdot. ha-1 in the young stand, and 1247.1 t .cntdot. ha-1 in the mature stand. Aboveground tree and detritus biomass were 49.0 t .cntdot. ha-1 and 130.2 t .cntdot. ha-1, respectively, in the young stand compared with 445.5 t .cntdot. ha-1 and 389.4 t .cntdot. ha-1 in the mature stand. Net primary production (NPP) was 18.3 t .cntdot. ha-1 in the young stand and 16.8 t .cntdot.ha-1 in the mature stand. Belowground dry matter production was 65% 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.