Organic carbon stocks in New Zealand's terrestrial ecosystems

The organic carbon in New Zealand's vegetation and soils has been estimated for 1992 from updated national databases of vegetative cover and soil carbon. These databases were augmented by inclusion of vegetation and soils information for Stewart Island, and addition of carbon estimates for upland and high‐country soils of South Island. Plant biomass estimates from literature were combined with the Vegetative Cover Map of New Zealand to give an estimate of 2420 Mt carbon for vegetation carbon above and below ground, including litter and humus. More than 80% of this carbon occurs in indigenous forested ecosystems on less than 26% of the land area, with only about 5% in planted forests. Soil organic carbon estimates for two depth ranges (0–0.25 m, 0–1 m) were derived from the N.Z. Land Resource Inventory, the Soil Map of Stewart Island, and the National Soils Database. Totals were 2500 ± 77 Mt and 4260 ± 190 Mt C respectively. Yellow‐brown earths made the largest contribution, with 727 Mt C in North Island and 489 Mt C in South Island, to 1 m depth. Nationally this soil group also contributed most to the error variance for soil carbon. A I:1 relationship (R, 0.68) over a wide range of soil C contents for soils sampled recently and 30–50 years ago under pasture suggested that under the same land use, uncertainties introduced by the use of historical soil data would not be large.