Decadal trends in plantation Pinus radiata (D. Don) forest growth

Abstract

Plantation Pinus radiata (D. Don) forests are longterm crops uniquely exposed to climate change; trees planted today and harvested after 2050 will experience multiple cycles of variable rainfall, along with an anticipated increase of another approximately 100 ppm in atmospheric CO2 (eCO2) and associated warming. While process-based modelling has suggested substantial increases in tree growth in higher-rainfall regions, empirical model outputs indicate the rate of
increases in productivity has slowed. We analysed three decades (1992–2022) of growth data across permanent
P. radiata plots in New Zealand to quantify recent trends in plantation productivity and to assess the implications of any decline for the sector, farm forestry and the wider economy. P. radiata growth increased by 25% from the 1990s to the 2000s but plateaued to a <5% gain in the 2010s, despite predicted benefits from rising eCO2, and continued adoption of improved germplasm, silvicultural practices and the practice of planting on landscapes with a pastoral history. The
age-class distribution became increasingly skewed towards recently established and younger plantations in later decades, which may partially mask underlyingchanges in productivity. These findings indicate that gains in forest productivity have slowed, highlighting the need for more targeted management interventions to maximise the benefits of eCO2 through efficient water and nutrient supply and utilisation.