Carbon Sequestration Estimates for Minor Exotic Softwood Species for Use in New Zealand’s Emissions Trading Scheme

New Zealand’s Emissions Trading Scheme (ETS) allows growers to receive payments through the accumulation of carbon units for increased carbon stock. For forests < 100 ha, growers rely on pre-formulated lookup tables (LUTs) to estimate changes in carbon stock by age. Currently, minor exotic softwood species, which are predominantly redwood and cypresses, are covered by a general Exotic Softwoods LUT. However, this table has been found to significantly underestimate carbon sequestration for these species. Using a combination of growth models and productivity surfaces, the objective of this study was to provide draft updates for the Exotic Softwoods LUT based on redwood, and two key cypresses (Cupressus lusitanica and C. macrocarpa), at different scales (national, Island level, regional), and to identify the most appropriate scale for a revised LUT. For cypress species, carbon predictions were made using C. lusitanica for the North Island and C. macrocarpa for the South Island, as these are the preferred species for each island. Variation in redwood carbon among New Zealand’s nine regions ranged over two-fold at ages 30 (390–847 tonnes CO2 ha−1) and 50 (926–1956 tonnes CO2 ha−1) and carbon was much higher within the North Island than the South Island. Predicted carbon for cypresses was higher within the North Island than the South Island at all ages and varied across regions, by 38% at age 30 (610–840 tonnes CO2 ha−1) and 12% at age 50 (1019–1146 tonnes CO2 ha−1). These findings suggest that a separate LUT for redwood is warranted, and that cypress species could serve as the default species for a revised Exotic Softwoods LUT. They also suggest that regional tables should be considered for both redwood and cypresses. However, the government may consider factors other than the technical considerations outlined here when updating the LUTs.