Forests and wetlands not only provide vital habitats for birds, fish and insects, they also sequester (store) carbon, which is vital to the health of our planet. Carbon storage helps to mitigate global warming and climate change, and to offset any carbon emitted by Tahi’s business activities.

Our goal is to ensure that Tahi always remains carbon neutral, and, at present, we’re well within this limit. As trees grow, they accumulate carbon in their woody tissues. From the outset, we’ve been restoring our landscape with native trees and shrubs – planting 325,000 trees since 2004 – and we won’t stop there: our pledge is to plant at least one million trees.

Already, this planting programme has resulted in the storage of more than 2,000 tons of carbon, primarily due to the carbon contained in the planted trees. This demonstrates the land’s enormous capability for storing carbon, once proper stewardship is developed.

THE CARBON EQUATION

At Tahi, our carbon footprint is directly linked to our accounting system. We follow a ‘reuse, reduce, recycle,’ philosophy across every facet of our business to further reduce this footprint.

The key to landscape recovery and sustainable business is getting the carbon balance right. We work hard to ensure Tahi’s business activities are carbon neutral, offset by our land’s capacity to store carbon.

We have now developed a programme to understand Tahi’s carbon storage capacity. Surveys, wetland and forest samples, and other data from the land have allowed us to paint a picture of our impact on the carbon economy.

CARBON STORAGE BY LAND USE

The numbers in this table represent the estimated carbon storage provided by different land uses, based on the soil and vegetation components. Often, only carbon in above ground vegetation is recorded, yet as we have shown, there are considerable stores of carbon in wetlands, for example.

However, International agreements, such as the Kyoto Protocol do not recognize soil carbon in ‘carbon accounting’ procedures, only carbon that has become stored due to planting. This is despite soil carbon having been extensively studied in agricultural science and its role in creating healthy soils.

Soil scientists been warning for years about the loss of soil carbon through poor land management. At Tahi, we take land management very seriously and have taken active steps to protect our soils, through cessation of cattle grazing and pest control. As time passes, we will see a gradual increase in soil carbon, along with the accelerating storage capacity of our planted vegetation.

WETLANDS STORE CARBON: TONS OF CARBON

Wetlands accumulate different amounts of carbon, depending on depth and water flow. All of Tahi’s recovering wetlands have organic soils that contain a significant amount of carbon: in some places, several metres deep.

All these areas are important landscape carbon stores, which until recent years, were slowly being destroyed. In fact, the carbon stored in Tahi’s wetlands amounts to many thousands of tonnes – in some cases, more than is stored in forests.

The way we manage Tahi means that no more carbon will be lost from these wetlands; in fact, the amount that can be stored will increase as the wetlands are re-established. Live update shown here or follow this link to see the carbon stored in Tahi’s wetlands.

Pull-out fact:

Did you know? Wetlands can store similar carbon levels per hectare basis as local native forests, or four times that of a pine plantation.

LEARN MORE ABOUT WETLANDS AND CARBON STORAGE

A former dune lake behind Tahi’s sand hills once occupied a depression several metres deep. It would have received vegetation remains over many centuries, but would only have had an outflow during major floods. Thus, it has retained all the carbon flowing in, as well as carbon from the vegetation growing there.

Other wetlands formed alongside streams meandering along the bottom of valleys. These tend to be shallower and subject to periodic disturbance, so would have accumulated carbon more slowly and hence contain less. It’s a similar story with wetland areas at the base of very steep hills – these would have had a fast through-flow of water, resulting in less carbon being able to accumulate in the soils.

To further complicate the story; in the distant past there was a shallow estuary running in behind the dunes and covering extensive areas near the shoreline. All this changed after a

massive volcanic eruption in the central North Island in AD200; most of the estuaries in northern New Zealand became choked with pumice and the smaller ones (as at Tahi) lost their connection to seawater. These areas then became shallow freshwater wetlands until they were drained in the early 20 th century.

Helping our planet,
tree by tree

Forests are recognized as valuable ‘carbon sinks’, though not all forests are created equal. Some trees are especially good at storing carbon in their trunks, branches and roots, whereas other plants such as rushes and grasses add carbon to the soil and wetlands, but store little in their leaves and roots. Which is why we plant a huge variety of trees! Native trees are relatively slow growing, although they continue to expand storage rates for 100 to 400 years, and then slowly decrease. For example, puriri trees grow quickly, they grow for most of their life (which can be very many centuries), and have a high carbon density wood.

Karaka trees also have the first three characteristics, but they have a low-density wood, so they have a different carbon value. Native trees also have the added benefit of positive biodiversity impacts, such as flowers, seeds and fruit needed for birds and insects, or in the case of wetland rushes and sedges, they help retain water and soil and provide habitat and shade for bird, fish and insect species.

Carbon storage by tree species

Carbon sequestration depends on three things: rate of growth, duration of growth (which in turn is dependent on longevity), and wood (carbon) density. Measuring carbon sequestration is no easy task, as different trees accumulate carbon at different rates and for different lengths of time (see fig.4).

At Tahi, we’ve established an independently verifiable system to measure carbon sequestration, taking into consideration our long-term goals of restoration and conservation of ecological values.

Technical References

Carbon by different species: based on work by Mark Kimberley, David Bergin and Peter Beets (2014). ‘Carbon Sequestration by planted native trees and shrubs’, Tane’s Tree Trust, Technical Article No. 10.5.
Parliamentary Commissioner for the Environment (2008). ‘Seeding the carbon storage opportunity in indigenous forests.’ Wellington: Parliamentary Commissioner for the Environment.

Wetland carbon storage: This is based on work carried out by Gabriela Ezeta Ramos in 2011 for her MSc Thesis at Auckland University, ‘Pasture to wetland reconversion: Analysis of soil organic carbon profiles and stocks’.

Tree carbon: based on a study in 2014 by Luitgard Schwendenmann and Neil Mitchell, ‘Carbon accumulation by native trees and soils in an urban park, Auckland’, New Zealand Journal of Ecology 38: 213-220.

Soil carbon: estimates are based on studies in 2004 by Mike Page et al, ‘Erosion-related soil carbon fluxes in a pastoral steepland catchment, New Zealand’, Agriculture, Ecosystems and Environment 103: 561–579. Also Bryan Stevenson in 2007, ‘Soil quality in Northland 2007: comparison with previous samplings in 2001’, Landcare Research Contract Report: LC0708/048.

Maps: Thanks to Austral Condor Ltd, for production of the wetland carbon storage maps.

Ecological analysis and interpretation: by Neil Mitchell and John Craig

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At one with nature.