At Tahi, we are driven by a singular purpose: to restore native ecosystem biodiversity. We have spent the last two decades regenerating our world-class nature sanctuary in the remote north of New Zealand.  Our pioneering, scientific approach goes beyond tree’s. We carefully consider all flora and fauna to accelerate the restoration of rich, biodiverse ecosystems and reduce carbon.

Biodiversity matters

According to the WWF there has been a 69% drop in monitored animal species since 1970 and 30% of tree species are under threat of extinction. This is not only detrimental to the natural world, but also to society as a whole. Loss of species can compromise food provision, economic development, public health, water security and the stability of communities. In terms of monetary value, the International Union for Conservation of Nature (IUCN) calculates that products and services provided by ecosystems are worth around US$33 trillion each year.

Moreover, biodiversity is a vital tool in the fight against climate change.

Despite the clear benefits, only a small proportion of the forests planted are biodiverse. Discover how Tahi has lead a pioneering biodiversity positive approach to native forest regeneration.

Creating healthy ecosystems

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 nonliving, 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 of the area 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 reintroduction 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 and regenerated over 8.4 million 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 20 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 25 endangered or protected species (there were only 14 originally)
  • 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
  • 3,300 tons of CO2e is estimated to be stored in the trees planted since 2004
  • 132,700 tons of CO2e is estimated to be stored in the soil and ecosystems due to our environmental measures

Measuring Carbon Storage

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.

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

The BVI: A Global Tool For Restoration 

Identifying species through tools like the BVI is key to the success of strategic restoration. The fundamental principle is that the right tree should be planted in the right place at the right time – and what constitutes ‘right’ will differ from place to place, whether in Aotearoa New Zealand or globally. 

The BVI serves as a window into the intricate dynamics of species interaction. It operates by not only attracting but also safeguarding key agents of transformation and dispersal, such as birds or keystone species. It is a practical and repeatable methodology that guides the decision-making helping to determine what to plant, where to plant it and the underlying rationale for these choices; layering it alongside technical data, modeling and field-tested results.

The BVI not only aids in identifying the right species, it also helps guide the purpose behind planting programmes, whether it’s for carbon sequestration, biodiversity enhancement, or a combination of both. This critical information can then be integrated with drone and satellite data, alongside carbon models; to offer a comprehensive glimpse into the future of the forest, delivering on its intended ecological, environmental and economic objectives.

Restoring Tahi’s Ecosystems and Our ‘Carbon Economy’

This image of a restored hillside at Tahi shows what strategic restoration can look like in practice, unveiling the dynamics of diversity and unseen alliances below ground. 

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 also have a role. 

On the left is one of New Zealand most notable keystone tree species, the pūriri (Vitex lucens). Its flowers, fruits and seeds are a valuable food source for many species, including the tūī (Prosthemadera novaeseelandiae), a bird important for ecosystem change. The pūriri’s dense foliage provides habitat and shelter for a diverse range of wildlife, while its trunk and roots help to nurture the local water and soil system. It grows slower than many of its counterparts, which alongside high wood density, makes it a more efficient long-term carbon sink, up to 1000 years. Its logs are also favoured by native Kiwi for nesting and roosting.

The pōhutukawa (Metrosideros excelsa), also has a BVI of 100. It fulfills a very similar role to the pūriri, albeit in an entirely different ecosystem (which is why you do not see it in this photo), however, they are not interchangeable. The pōhutukawa thrives on rocky cliff faces overlooking the sea, whereas the pūriri is suited to inland ecosystems. This demonstrates just how important it is to understand the characteristics of each tree and its surrounding habitat.

As the figure also shows, not every plant in a strategic restoration programme can, or should, have a high BVI. The kauri tree (Agathis australis), for example, only has a BVI of 47. This is because it does not directly support birds and larger species. It does, however, modify soil conditions and support plant species under its tree canopy, and is therefore invaluable in creating a healthy ecosystem.

Mānuka (Leptospermum scoparium), a prominent pioneer bush species in Aotearoa New Zealand, provides significant ecological support to invertebrates. Despite its low BVI of 10, it has an important role to play as part of the rich tapestry of species that together can transform an ecosystem. 

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.

Learn More About Sustainability:

At one with nature.