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Comparing regional variation in carbon sequestration for radiata pine and redwood throughout New Zealand

Authors: Michael S. Watt, Mark O. Kimberley
Publication: New Zealand Journal of Forestry, Volume N.Z.J.For. 2022, Issue N.Z.J.For. 67(1) 2022, pp 12–21, May 2022
Publisher: New Zealand Institute of Forestry

Abstract: New Zealand has committed to a net zero carbon target by 2050 that will require significant afforestation of fast-growing exotic species. An understanding of where best to plant important plantation species in the landscape is critical for optimising carbon sequestration for both individual growers and the country as a whole. This paper presents and compares national spatial surfaces of carbon for the two fast-growing conifers radiata pine and coast redwood under a range of stand ages (30, 40, 50 years) and stand densities (400, 650, 900 stems ha-1). When averaged across New Zealand and all scenarios, redwood was 6% more productive than radiata pine in the North Island (1,900 vs 1,799 tonnes CO2 ha-1), but 51% less productive in the South Island (690 vs 1,405 tonnes CO2 ha-1). Increases in carbon with greater stand density and age were markedly higher for redwood than radiata pine, and consequently redwood is particularly well suited for clearwood and carbon regimes with longer rotation lengths. Redwood generally outperformed radiata pine on warm, wet sites with moderate-to-high fertility, with gains highest in the West Coast, Taranaki, Waikato and Bay of Plenty. Radiata pine had higher carbon than redwood in cold and or dry areas and differences were most marked in Canterbury, Southland, Otago and Marlborough. Redwood should not be planted too close to the coast as it is salt intolerant and the species also requires shelter from strong prevailing winds. However, if redwood is correctly sited, and well managed during the establishment phase, it is capable of very high productivity on suitable sites. As predictions of carbon made here were derived from models based on fully stocked, well-managed permanent sample plots we recommend they are reduced by 15% before being applied to standard forestry sites.