14 August 2018

New Zealand-grown Pinus radiata will be taller and slimmer in the future according to a new paper. While sequestering greater amounts of carbon, the trees will be more exposed to risks from extreme winds and wildfire.

Researchers from Crown research institutes Scion and Manaaki Whenua have considered how climate change and future biosecurity threats might affect New Zealand’s plantation forests.

Considering the effects of increasing levels of carbon dioxide on photosynthesis, the productivity of radiata pine could increase on average by 10 per cent by 2040, and double that by 2090.

Lead author, Scion’s Dr Michael Watt explains: “Increasing concentrations of carbon dioxide in our atmosphere will increase the rate at which trees grow. An increased growth rate will result in trees becoming taller and more slender.”

This study indicates that the greatest threat to New Zealand’s plantation forests is likely to come from increased wind damage as increasingly slender and taller trees will be more susceptible to damage by future wind storms. The risks of breaking or uprooting can be reduced somewhat by modified forestry practices such as timely thinning and earlier harvesting, according to co-author Dr John Moore.

Very high and extreme fire risk days are also predicted to increase, with the length of the average fire season increasing by about 70% by 2040 and 80% by 2090. Fire scientist Grant Pearce found the most fire prone regions (Gisborne, Marlborough, and Canterbury) will remain the most at risk, but that the relative increase in risk is highest in Wellington and coastal Otago, where it could double and triple to 30 days and 20 days per season, respectively.

New Zealand is currently free of any significant damaging insects, but population levels and damage may increase in the future as warmer temperatures may provide an environment for foreign species and accelerate insect development. Weeds are likely to expand their range under climate change and compete more strongly with plantations.

“A decade’s worth of research into multiple climate change effects on New Zealand’s plantation forests has been summarised here,” says Michael Watt. “Determining the magnitude of climate change effects is crucial for informing national economic strategies, forest management and offsetting increasing carbon emissions as the country progresses toward a net carbon zero economy.”

Michael S Watt, Miko U F Kirschbaum, John R Moore, H Grant Pearce, Lindsay S Bulman, Eckehard G Brockerhoff, Nathanael Melia; Assessment of multiple climate change effects on plantation forests in New Zealand, Forestry: An International Journal of Forest Research, cpy024, https://doi.org/10.1093/forestry/cpy024