Pitfalls in greenhouse gas measures

Plantation forests can intercept rainwater and evaporate back to the atmosphere more than pasture...
Plantation forests can intercept rainwater and evaporate back to the atmosphere more than pasture. Photo: Getty Images
A sensible, integrated approach is needed to beat greenhouse gases by 2050, writes  Selva Selvarajah.

The increasing wider interest and engagement in tackling greenhouse gas emissions, including the aspiration for zero-carbon by 2050, are reassuring. The recent 620-page New Zealand Productivity Commission report on Low Emissions Economy recommended substantial afforestation, use of renewable electricity and land-use changes from livestock to cropping and horticulture by emission pricing. Broadly, there are two main tasks; reduction/avoidance of greenhouse gases at the source and mitigation.

At this crucial stage — from policy to legislation — it is timely for me to advise the lack of, or absence of, an integrated approach to reducing or mitigating greenhouse gases. An integrated approach considers any significant consequences of climate-change mitigations on natural resources, social, economy and culture. Such an approach avoids the situation of a "tale of blind men and elephant" and exposes any roadblocks before legislation. It is unfair to expect a heavily economy-centric commission report to adopt the above approach.

Let us consider afforestation as a mitigation option. The benefits of plantation forestry such as carbon storage, export and employment opportunities, reduced soil erosion in erodible catchments, improved stream water quality during growth phase and reduced flooding frequency and intensity in large-scale forestation are well known.

On the negative side, the plantation forest can intercept rainwater and evaporate back to the atmosphere more than pasture which could reduce stream flows and aquifer recharge. In some catchments, the water yield reduction may be 30% to 50%. Based on the New Zealand data, I assume, conservatively, more than 150 mm a year of rainwater could be lost by trees compared to pasture. Consequently, the 2.8 million hectares ( 10% of the country’s land area) upper limit afforestation recommended by the Productivity Commission mainly on sheep and beef land could sustain a water loss of 4.2billion cubic metres a year (1 cubic metre = 1000 litres).

Some may argue the forest intercepted rainwater can improve rainfall in large scale plantations. There is no compelling evidence in temperate countries to support that except for the contrary. Thus, any reduction in rainfall input in water-short catchments can only accentuate further problems. I am not raising any new issues here since "trading water for carbon sequestration" has already been raised by the international scientists and I am somewhat surprised  this issue has not featured in New Zealand policy making yet.

Fortunately, the forestry industry advocated Resource Management (National Environmental Standards for Plantation Forestry) Regulations 2017 which regulate plantation forestry (defined as: forest deliberately established for commercial purposes being at least 1 hectare of continuous forest cover.) restrict ad hoc afforestation.  Consents are required to plant trees under certain circumstances. However, if forestry is established for non-commercial purposes the above regulations do not apply, and consents are not required even in water-short catchments in the absence of relevant regional rules. Some regions (for example Canterbury and Tasman) have specific rules restricting forestry in rainfall recharge areas. Other regions may have to conduct their own hydrological assessments and if warranted consider any controls which will enable identifying suitable areas for afforestation.

To reduce carbon dioxide at the sources, increasing use of electric vehicles, industrial conversion to electricity and 100% renewable electricity energy are obvious options. However, since 19% of the electricity at peak is sourced from fossil fuels,  electric vehicles will be indirectly and partially powered by fossil fuels. Given the rapid electric vehicle uptake and the high potential for industrial conversion, there is urgent need for wind and geothermal energy to fill the gap which requires removal of, or dealing with, any consenting roadblocks. The commission endorses the above but it was buried in electricity and emission pricing synergy, hence the opportunity to provide decisive recommendations was lost. Consequently, the Commission did not cash in on substantial adoption of solar energy by households (using 32% of the electricity) which can complement increased use of electric vehicles and industry conversion.

As for methane and nitrous oxide, these have to be reduced or avoided at the sources. The Productivity Commission boldly predicts increasing emission prices could drive land use changes from livestock to horticulture or cropping which in turn will reduce methane and nitrous oxide emissions. Would such changes be possible with increasing nitrate leaching restrictions by regional councils when vegetable and kiwifruit growing and cropping are known to leach more nitrate than dairying or sheep and beef? Converting from dry livestock farming to horticulture also requires access to irrigation water, which is impossible in fully allocated catchments.

Inevitably, tackling greenhouse gases by policies or legislation solely on the basis of economy will be ineffective, with unintended consequences or roadblocks.

The safe, smooth and sustainable way of beating greenhouse gases by 2050 is by sensible integrated approach, be it policy or legislation, without stalling the current momentum.

- Dr Selva Selvarajah is an Resource Management Act consultant and researcher with Enviroknowledge.

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