Short rotation forestry could provide a pathway for New Zealand to replace 6% of its fossil fuel use, while also providing farmers in difficult country a valued biofuel crop option.
The latest work by Scion silviculture scientist Dr Alan Jones and his team estimates the reduction in fossil fuel use could be achieved with plantings over about 150,000 hectares of land, or less than 1% of New Zealand’s land area.
Jones presented his team’s research findings to a Bioenergy NZ seminar series aimed at exploring NZ’s options on alternative energy pathways to help meet its Paris Accord obligations.
He acknowledged short rotation forestry, which usually involves planting pines or eucalyptus, was an area that has been neglected for the past decade, after some intense interest prior to an international conference here in 2010.
Typically, the trees would be harvested at year 16, with Pinus radiata and three types of eucalyptus being most suitable. The eucalypt variety was dependent upon the site’s altitude and average temperature.
The researchers modelled the potential area needed based on valuations that ranged from placing a zero price on carbon through to $150 per tonne of carbon.
“We aimed to target land area that is ‘least cost’ or lowest value, particularly around Land Use Capability (LUC) 5-7.”
High risk “red zone” erodible country has been excluded, along with Department of Conservation land, existing forest and high value arable land.
When it comes to eucalyptus use, Jones acknowledged there is a North Island bias for the species, with a smaller economically viable area. At zero carbon payment that is about 90,000ha.
“As the ETS carbon value increases, the potentially economic viable area increases.”
The most suitable areas for short rotation plantation proved to be Northland, Central North Island, Hawke’s Bay, the east coast, Canterbury and Southland-Otago, based on distance and location relative to areas with higher energy demand.
Jones said transport costs are an acknowledged challenge with biofuel sourcing, but decentralised processing of the raw material could also impact an otherwise unsuitable area’s viability.
Biofuel plantations are reliant on investor confidence, and this could be boosted by the plantations still being capable of being pruned after year 10, and utilised in other applications including furniture making.
He said there has been much discourse about whether forestry bioenergy is offering a genuine climate mitigation alternative, boosted by the likes of the documentary Burned.
Preliminary analysis indicates that when used, every one tonne of biofuel displaces 1.3t of emissions from coal.
“It is effectively greater than that of carbon forestry, providing a fuel source carbon forestry does not.”
The mechanics of planting short rotation forestry involve high densities at about 750-1250 stems a hectare with no pruning carried out.
The type of tree required for biofuel is also placing quite different demands on tree geneticists and scientists, more acquainted with developing trees for high quality timber growth.
“Instead, we are trying to increase the energy density of these trees.”
The short rotation forests are expected to yield about 20-30t a hectare of biomass.
A recent Farmers Weekly visit to Brazil highlighted how the FS Ethanol company is using a combination of harvested bamboo and eucalyptus to fuel its corn ethanol plants in the western state of Mato Grosso.
That state faces an impending shortage of planted, sustainable forest fuel source by 2026 as corn ethanol production rockets. With all-bamboo fuel use, the company would be harvesting 25ha a day as biofuel.
The next step for researchers here is to get more trees in the ground to trial and analyse. A partnership with the Ministry for Primary Industries for trials has been established. Environment Canterbury has also expressed an interest in trial plots and outcomes.
Jones said NZ is in the lucky position of being able to grow such trees relatively quickly, compared to its European counterparts.
“It means we would be in a position to replace that fossil fuel carbon very quickly.”
Brian Cox, executive officer of Bioenergy NZ, said short rotation forestry also provides a way to fill a gap in wood supply that would emerge from about 2030.
NZ’s total wood production is expected to slide from 40 million cubic metres to 25 million cubic metres by 2038.
“These species also fit to a market driver that wants biomass in less than 25-30 years. It’s also a neglected opportunity for trees to provide erosion control. Short rotation crops are a key part of that.”
Scion has published a handbook for the industry on short rotation forestry, available here.
