New Zealand was once a land of birds. With the exception of bats, lizards and tuatara (an ancient reptile), birds were the dominant animals and filled our skies with wondrous song and flight. At Tahi, we’re passionate about rebuilding an ecosystem of birds: the kind that existed before mammals and pests were introduced to our land. We do this by planting trees that provide nectar, fruit and leaves, also shrubs, flaxes and ferns that provide habitat and shade for insects and other invertebrates, so our birds have plenty of food to eat – and the perfect spots for nesting. We’ve especially focused on birds that move seeds around the landscape, such as tui, kereru and silvereye. These birds are the natural architects of New Zealand ecosystems, the ‘agents of change’. Planting native trees and controlling pests are our way of re-starting these natural processes: ultimately creating a landscape of functioning, bio-diverse ecosystems including forest, wetland and open areas.

What’s more, our research shows that carbon is accumulating at Tahi, a sure sign that ecosystems are functioning and improving. Once nature has a helping hand, it starts to help itself. Since our restoration efforts began in 2004, we’ve experienced a multiplier effect. Today, Tahi is a story of regeneration. Of forests echoing to the calls of rare native birds. Of wetlands, lakes and streams that now teem with fish, invertebrates and insects. Of coastal sand dunes revived. Of centuries-old trees standing tall in forests that are now rejuvenating around them. You see, the more trees we plant, the more wetlands we revive, and the more birds, insects and fish we attract, the sooner we’ll regain the natural balance that once existed on our land.

A Bio-diverse Ecosystem is a Healthy Ecosystem

Healthy ecosystems and the organisms within them are vital for everyday life. They recycle and protect our water, soil and nutrients, and provide food, medicines and other resources. Healthy ecosystems with greater diversity are also more resilient and capable of withstanding natural disasters.

Tahi’s land was once a fertile haven, where Māori people thrived. With a deep belief in the spiritual sanctity of the land, Māori lived in harmony with nature for hundreds of years, believing that all components of ecosystems, both living and non-living, possess spiritual qualities. They also believe that people are the kaitiaki (guardians) of these ecosystems and have a responsibility to protect and enhance them – as we do, every day, at Tahi.

Cumulative Biodiversity

The graph represents the planting, wetlands and pest control that has taken place at Tahi since we began our restoration efforts in 2004, and the impact this has had on biodiversity.

  • In 2003 the pasture landscape at Tahi was dominated by 6 introduced grasses.
  • Most native animals did not use these areas.
  • The planting programme immediately began the re-introduction of native plant species.
  • To date 93 native plant species have been reintroduced to the landscape.
  • Different plants have different biodiversity ‘values’ – especially in the context of ecosystem restoration.
  • We have developed an index the – ‘Habitat biodiversity counter’ (1) that measures the extent to which the landscape is improving as a habitat for native wildlife.
  • Essentially the landscape had zero value in 2003 as a habitat for native wildlife,
  • As the landscape was replanted, its habitat biodiversity value rapidly increased and has continued to increase to the present day.

1. By multiplying the ‘biodiversity value’ * numbers of that species planted, an overall score can be generated for each year. The effect is cumulative.

Our Changing Landscape

Since 2004, we have:

  • Planted over 349,000 trees – 93 species of plants, including 19 species that are new to the landscape.
  • Reforested 14% of the land with native trees and shrubs.
  • Placed 9,157 metres of streams under protected management.
  • Restored 38.7 hectares of wetlands.
  • Created 4.5 hectares of lakes.
  • Protected 5 hectares of ecologically significant coastal sand dunes.

Today, we’re thrilled to say that:

  • 9 out of 15 local fish species have returned.
  • 71 species of birds have returned, including 23 endangered or protected species (there were only 14 origonally).
  • 141 vascular plant species have so far been recorded at Tahi and still counting, this includes 19 re-introduced species and at least 2 self-introduced.
  • 2,064 tons of carbon (7,497 tons of CO 2e) is estimated to be stored in the trees planted since 2004.
  • 7,031 tons of additional carbon (25,780 tons of CO2e) is estimated to have become stored in the soil and ecosystems due to our environmental measures.

Restoring Tahi’s Ecosystems and Our ‘Carbon Economy’

This image of a restored hillside at Tahi shows different ecosystem areas and how they work together to create biodiversity. On the left, is an area of surviving originalforest with a canopy of kauri, puriri and kahikatea trees, while on the the right, is hillslope planted in manuka (a typical early coloniser). Below that is a restored wetland with flax, cabbage trees, sedges and rushes.

The ‘biodiversity value’ (BV) of a plant species indicates its value to restoring Tahi’s ecosystems. Birds are the ‘architects’ of these ecosystems because they move seeds around the landscape, so the BV is especially weighted towards the attractiveness of a plant species to birds, as a food source and habitat. Invertebrates and reptiles alsohave a role, but these are less important in the early stages.

When revegetating our landscape, we plant some species of high biodiversity value, as well as more structural trees and shrubs. For example, manuka is an important structural species for revegetating landscapes – and it provides nectar for bees and other insects. Puriri is rated high for birds as it provides fruit, nectar and habitat for much of year, high for invertebrates as it provides habitat and food, plus it’s very long lived. Its logs are also favoured by native Kiwi for nesting and roosting.

Nature’s Amazing Carbon Storers

In terms of carbon, puriri is rated high as it can store carbon quite quickly and has very carbon dense wood. It’s also very long lived – which is important because puriri take carbon out of the atmosphere and store it for perhaps 500 to 1000 years. In the case of kauri, this carbon storage may last for 1000 to 2000 years, so you can see why it’s so vital to regenerate these native giants!

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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