9 Sep 2019

Scientists looking to marry native and exotic plantings

From Afternoons with Jesse Mulligan, 1:22 pm on 9 September 2019

Planting more radiata pine while maintaining our native forest is the best option for fighting greenhouse gas emissions - and should not add to the wilding pine problem, a forestry scientist says.

Forestry section in Port Underwood, South Island, New Zealand

Photo: 123RF

Pinus radiata, also known as Monterey pine, is unpopular for planting but it is one of the most effective trees in terms of removing carbon dioxide from the air.

The dilemma of planting to counteract emissions versus planting to restore native biodiversity is becoming all the more pressing as carbon dioxide levels continue ramp up and fuel climate change, while farmers are financially reluctant to relinquish productive land for trees.

University of Canterbury school of forestry professor Euan Mason tells Afternoons' Jesse Mulligan that tree planting cannot be the only solution to climate change. 

"All trees can do is get us there faster. It means we have to continue to maybe move our vehicle fleet to electric cars to make sure we generate energy without fossil fuels, to improve our farming systems, improve our fertiliser applications or for nitrous oxide, trying to find products that we can grow without putting lots of methane to the atmosphere, on our farm lands.

However, it will be necessary if New Zealand is to become carbon neutral. He says the evidence is there in The Globe Report, a study commissioned by all the parties in Parliament from British economic consultancy firm Vivid Economics. 

"The Globe Report set out to determine how quickly we could become the greenhouse gas neutral as a nation ...  they looked at all the sectors that are important in this debate, and came to a conclusion that without using forests the earliest we could get there, were likely to get there - like anything this is subject to debate, but they said - was probably around 2080, maybe 2100."

That would be too late to forestall the worst effects of climate change.

"The changes that are required to our behaviour, and to our systems, and to our technology are too great for us to get there by 2050 without using forests." 

The question then becomes what to plant. Prof Mason says the basic equation of photosynthesis involves taking carbon dioxide out of the atmosphere, combining it with water and converting it into sugars, which then become a source of energy for the tree but they also some of the some of the carbon is put into structural parts of plants. Some plants are better at this than others, and radiata pine is far and away one of the best - and better at it than native forest. 

"The sad truth is that this exotic tree, which a number of people don't like, is really effective at growing rapidly and soaking up CO2," he says.

pinus radiata

Pinus radiata Photo: 123RF

The need to counteract climate change needs to be balanced, however, against the value of preserving our native forests and their biodiversity, he says. 

"We have species and forests and ecosystems growing here that grow nowhere else and they support unique birdlife, and unique fauna of great variety, not just birds.

"We need to decide what's important and sometimes we do that with money, sometimes we do that through other values, that that we cannot quantify as money … it's because of those non-monetary values that we like to keep our native forest."

He says this biodiversity is valuable in itself and native forest should be preserved, but planting radiata is a valuable tool for forestry and presents the best option for emissions reduction. 

"Anything above 1400 is very, very rare indeed - tonnes per hectare - now, radiata pine will quite easily get to 1400 tonnes per year and it will go beyond that if it's planted in high density and unharvested."

Dispelling radiata myths: Non wilding, non souring

The problem is, radiata is considered something of a pest - but there are a couple of misapprehensions about the species which Prof Mason is happy to dismiss.

One of these is the problem of wilding pines - pest pine species which spread and grow rapidly strangling the bush where native forest once thrived - but Prof Mason says radiata tends not to be a wilding species. 

"Most of the wilding species that you see in the high country - species like Douglas Fir, Pinus contorta (lodgepole pine), Pinus nigra (Austrian/black pine), Pinus ponderosa - those are species that can survive much more readily and prosper and propagate themselves much more readily in harsh environments than radiata pine can, so given that 90 percent of our plantation estate is radiata pine, it's remarkable they’re almost never a wilding."

Wilding Pine eradication at Arapawa island  - before and after

Wilding pine eradication at Arapawa island - before and after. Photo: supplied

He says there are one or two rare exceptions where radiata can become a wilding. 

"If you're on a warm, wet site and there just happens to be very little grazing downwind - which of course rarely happens on a warm, wet site - then radiata pine can become a wilding ... but in most cases, wilding problems are not radiata pine.” 

The idea that pine plantations sour the soil beneath them and prevent future growth is also a misconception, he says.

"I can send you images that would show you native forest growing under plantations ... indigenous forests will eventually start to grow under under a radio pine plantation. The zones where you get forests that really have nothing much growing onto them in plantations are very dry sites or very cold sites - sites where you would have low biodiversity anyway."