The BVI

Beyond CO₂;
TAHI Bio
Value Index®

The Bio Value Index (BVI) is an innovative, science-based decision-making tool developed over two decades by Tahi, a nature reserve in New Zealand, to measure how indigenous tree species contribute to whole ecosystems. Beyond carbon, the BVI quantifies biodiversity and ecosystem health, serving as a vital tool for driving the transition to a biodiversity-positive economy.

The BVI incorporates data on a tree’s role in supporting animals, birds, invertebrates, carbon storage, and longevity. Birds, as global ecosystem architects, play a pivotal role in the index due to their seed dispersal and habitat creation. The BVI’s formula—BV% = (Bird + Invertebrate + Carbon) x Longevity—is a simple, cost-effective, and scalable methodology that can inform strategic decision-making globally, from technical applications to community-led projects.

This tool is instrumental in restoration projects, helping to determine what and where to plant for maximum ecological benefit. It supports a whole-ecosystem approach, enhancing resilience to natural disasters like floods, droughts, landslides, and fires, and fostering long-term forest regeneration.

The BVI challenges conservation efforts to go beyond single metrics like carbon, promoting a holistic perspective on ecosystem health. It is equally beneficial for farmers seeking to enhance land resilience, pollination, and water dynamics. Natural heritage and emphasizing the importance of endemic species, the BVI provides an accessible yet powerful framework to protect, restore, and rejuvenate ecosystems. Birds, serving as both indicators and catalysts of biodiversity, position the BVI as a tool that goes beyond measurement, driving meaningful and transformative action toward a sustainable future.

A Pioneering Approach: The BVI®

1. Longevity as an indicator of length of carbon storage (Extra long >500 yrs; Long 250-500 yrs; Medium 125-250 yrs; Short 60- 125yrs; Very short <60yrs).
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2. Carbon content based on wood density (Extremely
high >1000 Kg/m3; Very high 750-1000 Kg/m3;
High 500-750 Kg/m3; Medium 250-500 Kg/m3;
Low <250 Kg/m3).
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3. Carbon years index. Multiplied scores of longevity and carbon; longevity on a logarithmic scale, carbon on a linear scale. This is an indicator of how long and how much carbon will be stored.
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4. Bird and Invertebrate values indices. The importance
of a species to these two groups. NB in other regions, different/additional groups will be included in
biodiversity quality.
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5. Biosphere Value index. Carbon years index and Biodiversity quality index added together and rescaled to a 0-100 scale. The ‘bio value’ (BV®) of a plant species indicates its value to restoring TAHI’s ecosystems.
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6. Pines, provide no nectar or fruit to build or uphold an ecosystem from the ground up.

Why Is It Transformative?

The rapid decline in biodiversity is among the most pressing crises of our time. Global wildlife populations have dropped by 69% over the past 50 years, driven by habitat destruction, deforestation, and unsustainable land use. This collapse threatens ecosystems, humanity, and economic stability; with over half of global GDP dependent on nature. Despite its importance, biodiversity remains undervalued, with efforts often narrowly focused on carbon. A key barrier to progress is the lack of practical tools to measure biodiversity and its ecosystem contributions.

The Bio Value Index (BVI) bridges this gap, offering  a scalable, science-based tool to quantify biodiversity through a whole-ecosystem lens. By integrating factors like species richness, ecosystem services,  and carbon storage, the BVI helps prioritise restoration efforts, fostering resilience and driving a biodiversity-positive economy. Designed for universal application, the BVI empowers decision-making from boardrooms to farmers, ensuring biodiversity is measurable, actionable, and aligned with economic goals. 

The Bio Value Index (BVI) is transformative as it shifts restoration and conservation efforts from a narrow focus on carbon to a holistic, whole-ecosystem approach. By addressing biodiversity, ecological resilience, and long-term functionality, the BVI offers a data-driven framework for strategic restoration, particularly in degraded landscapes where natural seed dispersers like animals, birds and insects are absent. This accelerates ecosystem recovery, fostering thriving native systems.

Plants with High BVI®

Pūriri (Vitex lucens) is one of New Zealand’s most notable keystone tree species. Its flowers, fruits and seeds are a valuable food source for the majority of the year 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 is a surprisingly fast-growing tree, which alongside its high wood density, makes it an efficient long-term carbon sink, for perhaps a 1000 years. Its fallen branches and old trunks are also favoured by native Kiwi for nesting and roosting. The myriad benefits it provides for an ecosystem are reflected in its high BVI® value. The Pōhutukawa (Metrosideros excelsa), also has a BVI® value of 100. It fulfils a very similar role to the Pūriri, albeit in an entirely different ecosystem; however, they are not interchangeable. The Pōhutukawa thrives on sea cliffs and coastal landscapes, whereas Pūriri is found in the more inland ecosystems. 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.

Fig. 1 Pūriri

Fig. 2 Pōhutukawa

Important Plants with
Lower BVI®

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. Nevertheless, as an exceptionally long-lived canopy tree, it helps regulate forest temperature and environment. It also modifies soil conditions and provides support to plant species under its tree canopy, and is therefore invaluable in creating a healthy ecosystem. Consequently, it plays a crucial role in fostering a healthy ecosystem.

Mānuka (Leptospermum scoparium), a prominent pioneer shrub 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.

Fig. 3 Kauri

Fig. 4 Mānuka

Whitepapers

Tahi's rich twenty-year history in strategic restoration provides us with a unique platform to share our learnings. Our Science Centre acts as an extension of the Tahi vision – direct from our world-leading scientists, ecologists & environmentalists. Our vision is that these resources will help empower & inspire the world to act now.