Allocation of carbon in a mature eucalypt forest and some effects of soil phosphorus availability

Abstract

Pools and annual fluxes of carbon (C) were estimated for a mature Eucalyptus pauciflora (snowgum) forest with and without phosphorus (P) fertilizer addition to determine the effect of soil P availability on allocation of C in the stand. Aboveground biomass was estimated from allometric equations relating stem and branch diameters of individual trees to their biomass. Biomass production was calculated from annual increments in tree diameters and measurements of litterfall. Maintenance and construction respiration were calculated for each component using equations given by Ryan (1991a). Total belowground C flux was estimated from measurements of annual soil CO2 efflux less the C content of annual litterfall (assuming forest floor and soil C were at approximate steady state for the year that soil CO2 efflux was measured). The total C content of the standing biomass of the unfertilized stand was 138 t ha-1, with approximately 80% aboveground and 20% belowground. Forest floor C was 8.5 t ha-1. Soil C content (0–1 m) was 369 t ha-1 representing 70% of the total C pool in the ecosystem. Total gross annual C flux aboveground (biomass increment plus litterfall plus respiration) was 11.9 t ha-1 and gross flux belowground (coarse root increment plus fine root production plus root respiration) was 5.1 t ha-1. Total annual soil efflux was 7.1 t ha-1, of which 2.5 t ha-1 (35%) was contributed by litter decomposition.