Q+A - The 1 Billion Trees Programme

What is it?

The One Billion Trees Programme is a Government initiative targeted at increasing the current rate of nationwide tree planting to reach at least a billion trees by 2028.

What is its purpose?

Forestry New Zealand believes the one billion trees programme will:

-          improve land productivity

-          tackle environmental issues like erosion

-          reduce emissions through CO2 absorption

-          improve water quality

-          provide important habitats for a range of native species

-          enhance natural landscapes

-          provide another source of income from timber, honey and carbon credits

-          support well being and create jobs and careers for our people.

Two of these outcomes – emission reduction and improved water quality – fall directly under two of the government’s most important long-term environmental goals. One is to make 90% of New Zealand rivers swimmable by 2040, the other, to reduce carbon emissions to net-zero by 2050.

How many trees are currently planted annually?

At the moment, the replanting rate by commercial foresters is around 50 million trees a year. Therefore, the yearly replanting rate needs to double in order to achieve the one billion target (10 x 100 million trees).

Is the one billion trees target possible?

Forest Owners’ Association president Peter Weir says yes. Why? Because we’ve done it before. According to Weir, over a billion trees were planted in the 1990s.

Who is involved?

The programme is funded by the Provincial Growth Fund (PGF), and led by Te Uru Rakau (Forestry New Zealand) within the Ministry for Primary Industries.

How will the One Billion Trees Programme improve water quality and reduce carbon emissions?

When planted in close proximity to rivers, lakes and streams, forests aid water health by filtering out sediments and other pollutants from runoff. Creating these ‘forest buffers’ slows the flow of water into bodies, allowing suspended sediment to fall out and subsequently reducing phosphorous levels, as many forms of phosphorous attach to sediment. Forest buffers also filter nitrogen, pesticides, herbicides, and coliform bacteria.

Forests also play a role in reducing carbon emissions through a process known as carbon sequestration. During photosynthesis, CO2 is absorbed from the atmosphere by trees and stored as carbon in the biomass (trunk, branches, foliage and roots). As described in Principles and Processes of Carbon Sequestration by Trees, this absorption “offers a significant offset against continuing greenhouse gas emissions and may be combined with other benefits such as timber production, environmental protection, added biodiversity and land rehabilitation.”

How much will it cost?

Already, almost half a billion dollars has been committed to the project. Its total cost is projected to exceed $2 billion.  

What are the key obstacles facing the programme?

Encouraging buy-in

Many feel the biggest obstacle to getting the planned 1 billion trees planted by 2028 is buy-in from landowners. In a July article for Stuff, Andrea Fox talked to Peter Weir of the FOA, who said:

“We had this strategy [1 billion trees] in the 1990s but land prices were different then. "They're now out of reach of commercial forestry owners – no large companies have got unplanted land in the land bank. That leaves farmers, Māori landowners, Crown Forestry, local councils and Joe Public to plant the rest. You have to ask what are the things that will make a farmer or owner of unplanted land suitable for afforestation plant it.”

Weir believes the answer could be to involve farmers in the ETS, giving them an incentive to offset carbon emissions.

Additionally, the forestry sector is expected to surplus land, a fact made clear by Shane Jones in an interview with the AM Show:

“Seventy percent of the forestry sector is already owned by foreigners. With the right sort of incentives and improvements to the Emissions Trading Scheme they're telling me they can boost their contribution. With the billion-dollar fund dedicated to forestry, mark my words, I've got officials finally realising they have to surplus land to avoid them becoming redundant.”

Defining a carbon forest

Another big obstacle facing the 1 billion trees programme lies in the current definition of a carbon forest, and how this definition affects farmers.

According to the Ministry for the Environment, a carbon forest must reach a height of at least 5 metres, be over 1 hectare in total size, and have more than 30% canopy cover.

Back in early 2017, then-Federated Farmers president William Rolleston noted that under these parameters a farmer could plant trees for an area of erosion or a shelter belt, yet not receive carbon credits for the planting because it failed to meet one or more of the Ministry’s criteria, which were devised before the accurate plantation mapping technology of today was available.

With current drone-assisted mapping capabilities, working out the quantity of carbon stored in trees is much easier than it once was.

If the old definition of a carbon forest is removed, this technology could allow farmers to be rewarded for every individual tree they plant, increasing their incentive to do so.

Reduction in water yield

In experimental studies conducted around New Zealand, reductions in annual water yield of between 30-80% have been measured following afforestation of pasture.

Essentially, the issue is that tall vegetation (i.e. trees) used as land cover results in less water reaching a stream or underlying aquifer than short vegetation (i.e. pasture). For this very reason, restrictions on afforestation have been instigated in some regions (Tasman, Canterbury) with the intention of protecting water yield.

Increasing the vegetation canopy cover affects the water balance through an increase in evaporation, which reduces the amount of water available for runoff and stream flow.

Evaporation can be split into transpiration (dry leaf evaporation) and interception loss (wet leaf evaporation).

Transpiration: the process of water movement through a plant and its evaporation from aerial parts, such as leaves, stems and flowers. 97 to 99.5% of the water taken up by a plants roots is lost through transpiration and guttation.

Interception loss: the percentage of rainfall intercepted by the canopy and then evaporated directly back into the atmosphere.

A range of studies investigating afforestation and water yield have been conducted in small research catchments in New Zealand over the years. From these studies, and similar studies conducted overseas, the following points have become apparent:

  • A reduction in tall vegetation cover causes an increase in water yield, and vice versa

  • Increasing scale of vegetation cover (both upwards and outwards) in a catchment does lead to a decrease in water yield, but there is much spatial and temporal variability that needs to be taken into account.

  • With respect to the vegetation type, the amount of increased annual water yield per 10% decrease in vegetation cover can be generalised.

  • Reductions in vegetation cover of less than 20% of an area cannot be detected by measuring stream flow

  • The use of percentages to report changes in total water yield is convenient for comparison but may be deceptive.  For example, a 10% reduction in annual water yield at a high rainfall site may be considerably less important ecologically than the same percentage reduction at a drier location.

The onset of the 1 billion trees programme will bring the issue of water yield reduction into the spotlight throughout New Zealand, and will likely be a point of considerable contention between water users and planters.

For more detail on forestry and water yield, click here.


Information sourced from:

Unwin, G.L and P.E. Kriedman. “Principles and Processes of Carbon Sequestration by Trees.” Research and Development Division State Forests of New South Wales Sydney. 2000.

Fox, Andrea. “Ten years, 1 billion trees - making the numbers add up.” Stuff. 2018.

Prendergast, Ella. “Government short on land for 1 billion trees promise.” Stuff. 2018.

Forestry NZ (MPI). “One Billion Trees Programme.” mpi.govt.nz. Last reviewed: 2018.

Davie, Tim and Barry Fahey. “Forestry and water yield; the New Zealand example.” Landcare Research.

Q+A - Forestry and debris flows

Roughly 7% of New Zealand’s total landmass is covered by exotic plantation forests.

The forestry industry contributes an annual income of around $5 billion to our economy, makes up 3% of GDP, and provides jobs for close to 20,000 people.

Forestry is undeniably important to New Zealand – socially, economically, and even environmentally. As our government pushes towards an ambitious ‘carbon zero by 2050’ goal, the role of planted forests in removing CO2 from the atmosphere through photosynthesis (a process termed ‘carbon sequestration’) will become vital.

Source: USDA, Northern Research Station.

Source: USDA, Northern Research Station.

However, forestry also has its downsides, and one of them, the increasing occurrence of debris flows, needs to be addressed.

In the following Q+A we’ll take you through the ins and outs of debris flows, how they occur, what their effects are and how they might be managed more effectively in the future.

What are debris flows?

Debris flows are described by the NZ Forest Owners Association as “very rapid to extremely rapid surging flows of saturated debris in a steep channel.”

They tend to contain a 60-80% concentration of sedimentary material (matter that settles to the bottom of a water body, e.g. sand, silt, pebbles, clay) and may or may not also hold woody material from forestry.

Debris flows usually move in surges, growing gradually in mass through entrainment (surface sediment picked up by a fluid flow and incorporated into a larger body).

Debris avalanches or shallow landslides can transform into debris flows once they become confined to a channel.

How do they occur?

The primary cause of a debris flow, as described by the NZFOA, is the “generation of sediment by mass movement into a channel.”

This generally occurs when a land area characterised by high, steep slopes and plentiful sedimentary ground matter is hit by heavy rainfall, causing large volumes of debris to erode vertically into a channel. Once the flow begins, it is generally only halted by a change in gradient or a reduction in flow depth, e.g. - on a fan or where a steep stream exits onto a flood plain.

Planted forests which sit in the post-harvest, pre-canopy closure phase (which usually lasts 5-6 years) typically contain high volumes of sediment, putting them in what is known as the ‘window of vulnerability’ for debris flows.

During this time, the removal of the forest canopy leaves the soil exposed to rainfall, making it increasingly vulnerable to surface erosion and water infiltration. Additionally, as the trees have been felled, their remaining roots begin to rot, reducing their soil reinforcement capacity.

When a period of high rainfall hits an area of forest in the ‘window of vulnerability’, debris flows tend to occur.

What are the impacts of debris flows?

Debris flows from forestry can have devastating effects on nearby towns and infrastructure, a fact highlighted by two recent examples in New Zealand.

In February of this year, in Marahau, a period of extremely high rainfall (brought on by Cyclone Gita) caused a huge flow of sediment and forest debris to descend from the hills, smashing property fences, damaging buildings and exposing residents to serious injury.

Two months later, an even larger debris flow damaged a total of 61 bridges and culverts in the East Coast district. This, again, was a product of extremely high rainfall and vulnerable forestry land.

In the Mangakahia Valley, Northland, poorly planned planting in the ‘80s has created consistent issues with debris flow. In 2003, resident Bruce Alexander carried out a survey for Carter Holt of the damage caused to local waterways from planting on soft soil and steep slopes.

His photographs show pines planted right down to the riverbanks, toppling into the water, taking big chunks of the bank with them, turning the stream brown with silt and creating dams as waste timber built up behind them.

Overseas, debris flows have washed away entire villages, destroyed agricultural lands, resulted in fatalities and had environmental impacts like loss of habitat, increased siltation of waterways and changes in topography.

How can debris flows be minimised?

As the NZFOA states, debris flows are a natural process, and therefore they cannot and should not be prevented altogether. However, their increasing frequency – a product of plantation forestry – can be curbed, provided careful planning is put in place.

NZ Forestry identifies the following six measures as integral for reducing both the occurrence of debris flows and the environmental + economic damages they cause:

1) Hazard avoidance. Identify areas where debris flows are likely to occur and take note of infrastructure (roads, bridges, buildings) and people that may resultantly be affected.

2) Defence/channelling structures. In areas where risk to infrastructure and life is high, introduce structures (slash racks, driven railway irons) that may mitigate risk by trapping or channelling debris into storage areas for management and disposal.

3) Narrowing the window of opportunity. In order to reduce the 5-6 period in which forestry soils become vulnerable to water infiltration and erosion, replant at a higher stocking density. Additionally, look into planting species that maintain live roots after harvest.

4) Riparian management. Riparian planting on lower slopes has been known to trap and impede debris flows. It is important however, that careful logistical planning is undertaken to prevent riparian plants being entrained into the flow.

5) Longer rotation crops or retirement into permanent forest cover. Identify areas most vulnerable to landslides and debris flows and consider a change to rotation length or conversion to permanent forest cover.

6) Improved risk models. Current data on risks and mitigation options for forestry management is widely considered inadequate. Collection of standardised data on size, frequency and impact of debris flows as a part of routine forest monitoring operations will enable the improvement of risk models, and the more effective management and mitigation of the impact of debris flows.

The Labour government’s emissions-curbing plan to plant 1 billion trees over the next ten years will require careful planning to ensure the risk of debris flows, along with other afforestation-related hazards, are minimised.

The Eastland Wood Council’s 2018 publication “Our changing landscape” highlights the vulnerability of the Gisborne region to debris flows and emphasises the need to reduce their occurrence when further planting occurs there over the next decade:

“The Gisborne East Coast is part of a plate collision crush zone. It is geologically fragile, with our steep hillsides formed as a consequence of natural erosion and land uplift, something that has been going on for thousands of years and it is not stopping. Weak underlying geology, with recent thin soils on top, steep slopes, rapid down-cutting by rivers (due to the rate of uplift) and periodic high rainfall and high intensity storm events mean erosion rates are naturally high. The main form of erosion is mass movement — and under forests this will mean debris flow.”

Photos taken in the Tapuaeroa Valley show the effects of erosion from forestry. Credit - Eastland Wood Council.

Photos taken in the Tapuaeroa Valley show the effects of erosion from forestry. Credit - Eastland Wood Council.

It mentions the measures previously stated for risk mitigation, and additionally notes species change:

“Under the Government’s 1 Billion Trees programme there is an opportunity to look at other species, particularly for red-zoned land, and to understand the benefits of them. Many forest owners are also investigating tree species along riparian margins.”

Strategies like these will continue to be studied and trialed by the industry as it works with researchers, regulatory bodies, communities, and Government agencies to develop and improve best practice and ensure that the future planting of forests, both exotic and native, is something that helps – not hinders - people and the environment



Q+A - Soil Carbon

The Pastoral Greenhouse Gas Research Consortium is dedicated to mitigating greenhouse gas emissions from the agriculture sector by educating farmers and providing them with the tools to work at reducing their own carbon footprint. The following information is taken from their fact sheets on soil carbon, which show us why it is important and how it can be measured and stored for the benefit of both the agriculture sector and the environment.


Soil carbon is an intrinsic part of everyday life on earth; it is the basis of soil fertility, releases nutrients for plant growth, promotes the structure, biological and physical health of soil, and is a buffer against harmful substances.

Soil carbon results from the interactions of ecological processes - namely the feeding of microbes on decomposing matter - and can be affected by human activities that disrupt these processes.

The important issue is how we humans limit our impacts on these processes and work to keep carbon stored in the soil, rather than let it be released into the atmosphere.


There is more carbon in soil than terrestrial plants and the atmosphere combined. Practices that increase the amount of carbon stored in soils cab offset some of the greenhouse gas emissions from agriculture. Conversely, practices that deplete soil carbon and release it back into the atmosphere can increase emissions from agriculture.

The total carbon content of New Zealand soils isn’t the issue, rather it’s how that total changes over time.


Carbon is constantly being moved between the atmosphere, plants, and soil.

During photosynthesis, plants algae and some micro-organisms use sunlight to convert CO2 and water into sugars that are incorporated into their cells – some of which are consumed by animals.

Decomposing animal material, plant matter, fungi, worms and an array of micro-organisms contribute carbon to the soil. Most of this matter quickly decomposes as microbes feed on it and release the CO2 back into the atmosphere as they respire.

However, a small proportion of it becomes tightly bound to the mineral surfaces of soil particles, or tightly trapped in soil clumps, where it is protected and less accessible to microbes. It can remain locked away in this ‘stabilised’ state for hundreds of years.

The question is how you increase the amount of carbon stored in soils, therefore reducing the amount released into the atmosphere.


There aren’t yet any robust rules around reliably storing carbon in New Zealand’s pasture soils.

It is important, first, to maintain current stocks, as carbon can be lost quickly and recovered only slowly.

Beyond that, increasing soil carbon breaks down into two categories:

  •      Add more carbon and stabilise that carbon in the soil.
  •      Stabilise more of the existing input and reduce carbon turnover.

Research has shown that overgrazing reduces soil carbon, as it reduces overall plant cover and carbon inputs via roots. However, under grazing may equally contribute to soil carbon loss.

There are several options for increasing soil carbon currently in practice, though all of them need further research to determine their effectiveness under NZ conditions, and whether they are restricted to certain soil types, climatic conditions or management practices.

The First:

Add Nitrogen - The addition of nitrogen fertilizer or clover fixation might increase soil carbon in the short term, but in the longer term, it reaches a plateau. This option needs further testing, and it must be noted that it may create undesirable side-effects like the production of nitrous oxide.

The Second:

Optimise Irrigation - This should increase soil carbon due to increased plant growth and greater inputs of carbon into the soil, and hence remove carbon dioxide from the atmosphere. However, irrigation also encourages greater soil microbial activity, which in turn would convert this soil carbon into C02 and release it back into the atmosphere. Again, more research is needed.

The Third:

Increase Root Inputs of Carbon - Increasing the amount and turnover of roots should deposit more carbon into the soil, where some of it would be incorporated into stable soil organic matter. This method is currently being researched with tests on different pastures to see which is most effective. Mixed swards and plant species have previously shown to have the greatest root biomass and turnover, but more research is needed, particularly into how different pastures affect milk and meat production.

The Fourth:

Add Biochar - There is strong evidence that Biochar represents a very stable form of carbon, so it could be used to store more carbon in soils. The main challenge at present is the cost of the material, and the wide areas it would need to cover, which make Biochar an economically unfeasible solution for NZ.


Scientists estimate that an increase in soil organic carbon stocks of 0.4% per annum would compensate human-induced greenhouse gas emissions on a global basis. Soil carbon also provides a source of nutrients, helps particle aggregation, increases water storage and protects from soil erosion and compaction. These factors can significantly improve food production.


Measuring soil carbon and how its levels change over time, is a costly and labour-intensive exercise. This is because soil carbon can vary significantly from paddock to paddock and year to year.

Traditionally it is done by extracting soil cores and analysing their carbon content in a lab. However, this method limits the ability to make a credible farm-scale measurement.

If data points are too sparse, they could give a misleading picture of the average or total soil carbon stocks across an entire farm.

If we are to increase our ability to characterise and monitor these changes in soil organic carbon stocks, we need to develop rapid, practical, accurate, and cost-effective methods that combine spot measurements with robust tools to interpolate between data points across the diverse landscapes spanned by typical New Zealand farms. Recent research is opening exciting and cost-effective opportunities to make farm- and paddock-scale sampling and estimates of soil carbon more affordable and accurate.

For example:

  • Soil Spectroscopy: Soil Spectroscopy is a sensing technology developed to accelerate the prediction of soil properties. It relies on the fact that the reflectance of light from a soil surface is related to the bonding and stretching vibrations of molecules in the soil. The issue with this method is that it’s time and cost-effective. However, Internationally, soil spectroscopy is acknowledged as a major advance in the estimation of soil carbon, and other soil properties, allowing many more values to be estimated for the same time and cost as traditional analytical methods.
  • Digital Soil Mapping: Digital Soil Mapping uses environmental datasets along with advanced modeling methods (e.g. geostatistics, data mining) to develop spatial models of soil properties such as soil carbon. This method has been employed successfully in the Hawkes Bay Region and is being evaluated by regional councils throughout the North Island.


  • Soil carbon supports healthy and productive farm systems, and greater understanding of the distribution and changes in soil carbon across farms can help farmers adjust and improve management of this essential resource.
  • Soil carbon sequestration could offset some greenhouse gas emissions that are currently difficult to reduce otherwise
  • New soil spectroscopy and digital soil mapping technologies help reduce the uncertainty of soil carbon stock and stock change predictions, enabling soil carbon stock changes to be monitored at farm scales

As global warming continues to intensify, it is essential that emission-reducing strategies like these are studied, tested and employed.

For more information on soil carbon, visit www.nzagrc.org.nz