Afforestation/reforestation of New Zealand marginal pasture lands by indigenous shrublands: the potential for Kyoto forest sinks

New Zealand will use the afforestation/reforestation (A/R) provisions of article 3.3 of the Kyoto protocol to help offset greenhouse gas emissions during the first commitment period, 2008 to 2012. We assess here the potential initial C sink available from A/R of marginal pasture lands by New Zealand's most common shrubland species: manuka (Leptospermum scoparium) and kanuka (Kunzea ericoides). Plotbased mensuration shows that mean net C accumulation rates for manuka/kanuka shrubland are in the range 1.9 to 2.5 t C ha(-1) yr(-1), when averaged over the active growth phase of about 40 years. Estimates of the change in mineral soil C with shrubland A/R of grassland suggest small losses occur, although these appear to be largely offset by accumulation of C in the litter layers. Analysis shows that nationally there are about 1.45 Mha of marginal pastoral land suitable for A/R by indigenous shrubland or forest. This area could accumulate about 2.9 +/- 0.5 Mt C yr(-1), a significant offset to New Zealand's annual energy-related CO2 emissions of 8.81 Mt CO2-C yr(-1). An initial economic analysis of livestock farming for a region with large areas of land marginal for sustained pastoral agriculture suggests carbon farming may prove an attractive alternative land use if international prices for biomass-C reach about EURO10 per tonne CO2.