Defining sustainability of plantation forests through identification of site quality indicators influencing productivity-A national view for New Zealand

Volume increment over the two-year period was most strongly influenced by site, ranging 50-fold and 15-fold across sites for C. lusitanica and P. radiata, respectively. For the treatments, species accounted for most of the variance in increment, with mean volume increment across all sites of P. radiata significantly exceeding that of C. lusitanica by 56%. Fertilisation also significantly influenced volume increment inducing mean gains of 30%. Disturbance had a significant, but comparatively weak effect, reducing mean volume increment by 9%. After correction had been made for environment (temperature and rainfall), soil properties that were most strongly related to volume increment for both species included CN ratio, total soil nitrogen, total soil phosphorus, organic phosphorus and depth of the A horizon. When soil properties were included in combination, the best predictive models of volume increment formulated for both species included rainfall, temperature, the product of total soil nitrogen and total soil phosphorus and depth of the A horizon.