A spatial comparison of redwood and radiata pine productivity throughout New Zealand

Authors: Michael S. Watt, Mark O. Kimberley, Simon Rapley, Rob Webster
Publication: New Zealand Journal of Forestry, Volume N.Z.J.For. 2021, Issue N.Z.J.For. 66(3) 2021, pp 33-41, Nov 2021
Publisher: New Zealand Institute of Forestry

Abstract: Coast redwood (Sequoia sempervirens) is a very productive and long-lived conifer that constitutes less than 1% of New Zealand plantations. Despite the potential of redwood, little research has compared its productivity with radiata pine which comprises 90% of plantations. This paper describes a recently developed growth model for redwood and compares national maps of productivity for redwood and radiata pine that have been recently published. These productivity maps were used to generate regional comparisons of both species at ages 30, 40 and 50 years, under a clearwood regime, for areas that were suitable for redwood. On average, within the North Island, redwood was 8% more productive than radiata pine at age 30 (mean total volume of 972 vs 901 m3/ha) and this gain increased to 45% by age 50 (total volume of 2,186 vs 1,505 m3/ ha). At a regional level, volume gains for redwood were largest for the Waikato, Taranaki and the Bay of Plenty, where increases over radiata pine averaged 60%, 57% and 56%, respectively, by age 50. Redwood was more productive than radiata pine within many northern areas of the South Island with moderate-to-high rainfall. However, within most eastern and southern sites in the South Island radiata pine had higher productivity, reflecting the higher sensitivity of redwood to cold, dry conditions. Redwood produces a very stable appearance grade timber with low shrinkage that has a higher value per cubic metre than radiata pine. The wilding risk from redwood has been rated as very low and the species is an ideal choice for erosion control. Redwood has no major insect or disease problems and is resistant to damage by fire and wind. In combination with the high growth rates documented in this paper these factors demonstrate the considerable potential of redwood for further afforestation within New Zealand. Further research should collect more redwood growth data from Northland and areas that were projected to have high productivity in the South Island to improve confidence in model predictions.