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.