Comparing volume productivity of redwood and radiata pine plantations in New Zealand

Abstract

Coast redwood (Sequoia sempervirens) is a productive conifer that has considerable potential as a plantation species within New Zealand where radiata pine (Pinus radiata) comprises 90% of plantations. However, little research has compared volume productivity on the same basis between radiata pine and promising species such as redwood. Radiata pine volume productivity can be described by 300 Index, which quantifies its mean annual increment at age 30 for a stand density of 300 stems ha−1. Using New Zealand redwood growth data from 130 plots, the objectives of this study were to (i) develop a model of redwood 300 Index productivity, (ii) compare fine scale (25 m) spatial predictions of 300 Index from this model with previous national predictions of 300 Index for radiata pine and (iii) undertake species comparisons of volume productivity across a broader age range for contrasting stand densities and values of 300 Index.Measurements made within the plot dataset demonstrated the high productivity of New Zealand grown redwood with maximum mean top height and volume reaching, respectively, 59.1 m and 4,293 m3 ha−1 for an 84 year old stand. Redwood 300 Index ranged 15-fold within the dataset from 4.36 – 64.8 m3 ha−1 yr−1 (mean = 22.8 m3 ha−1 yr−1; SD = 11.7 m3 ha−1 yr−1).The multiple regression model that was developed to predict 300 Index from environmental and stand variables fitted the data well (R2 = 0.66, RMSD = 6.80 m3 ha−1 yr−1). The 300 Index surfaces show that redwood volume productivity was on average 8% higher than radiata pine within the North Island, but on average 33% lower than radiata pine in the South Island. Species comparisons of volume over time, for three contrasting site qualities (300 Indices), showed that redwood markedly outperformed radiata pine, at ages older than 30 years for final crop stand densities of 300 stems ha−1 and this species divergence in volume increased at 600 stems ha−1. The developed surfaces highlight the potential of redwood for further afforestation within New Zealand.