Do the indigenous forests affect the net CO₂ emmision policy of New Zealand?

Authors: G.M.J. Hall, D.Y. Hollinger
Publication: New Zealand Journal of Forestry, Volume N.Z.J.For. 1996, Issue N.Z.J.For. 41(4) 1997, pp 24-31, Jan 1997
Publisher: New Zealand Institute of Forestry

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Abstract: Concern with rising greenhouse gas levels and climate change has led the New Zealand Government to sign international agreements to construct carbon budgets and control greenhouse gas emissions including CO,. Government policy on CO, emissions assumes the indigenous forests are "carbon-neutral", neither gaining nor losing carbon. To test this hypothesis, data were pooled from surveys, done over the last 35 years, throughout South Island and Stewart Island indigenous forests. Tree diameter and height data from 5965 permanent plots (178 species) were used to estimate total carbon, and 1829 remeasured plots (134 species) were compared to estimate annual change. Total stem volume was estimated from diameter by species diameter/ height equations, mean plot canopy height, and a parabolic volume equation. Volumes were converted to biomass using basic wood density.

Total carbon in the above-ground stems of the South Island and Stewart Island indigenous forests was estimated at 483.1 ± 2.99 million Mg (95% CI) over 3.25 million ha of forest with an annual net loss of 1.8 ± 1.5 million Mg C yr'. Changes are not uniform throughout the indigenous forests; loss of live-carbon is predominantly from the podocarp-broadleaved areas. Carbon losses appear to be greatest in areas impacted by large populations of introduced wild animals. The net-emission policy includes increasing new land planting of exotic forests to average 100,000 ha yr'. To offset estimated mean carbon losses from the South Island and Stewart Island indigenous forests the area of plantation forest (mean ~ 13 years old) would have to be increased by 29,000 to 36,000 ha yr'. Extending this result to all New Zealand's indigenous forests and assuming similar forest trends occur in the North Island, plantation area would have to be increased by 46,000 to 58,000 ha yr'. These preliminary results suggest the indigenous forests could impact strongly on Government policy.

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