In addition to our assessment of the ‘biodiversity attention’ of projects and the evaluation of project overlap with protected areas, we have been busy trying to find a variable that captures the biodiversity value of nature-based carbon projects. Despite reporting on the unreliability of some nature-based projects when it comes to carbon, they could still be able to provide much-needed funding for both the protection of biodiversity hotspots and the restoration of ecosystems that have been highly disturbed. That is useful information in the assessment of biodiversity as a co-benefit. Finding one biodiversity value is tough, since it is such a multifaceted concept. So we adopt the concept of ‘ecological integrity’ to generate preliminary insights on the potential and practice of nature-based carbon projects.

Understanding Ecological Integrity

‘Ecological integrity’ is used as an umbrella term for a variety of indices, which describe the intactness of various aspects of ecosystems, including their structure, composition and functioning. The idea is that ecosystems with higher integrity are less degraded, and that those with lower integrity values are more depleted by human interference. One of the most popular integrity indices is the Biodiversity Intactness Index (BII), which was developed by the Natural History Museum. 

The Biodiversity Intactness Index estimates how the average abundance of native terrestrial species in a region compares with their (estimated) abundances without significant human impacts. It ranges from 0% to 100% intactness. It is widely used as a way of describing the extent of human impacts on ecosystems around the world. We are planning on using it for our biodiversity scoring product in two ways: the identification of conservation priorities and restoration opportunities. These map onto the two broad types of nature-based carbon projects (conservation and restoration) we classified in our methodology blog.

Determining Key  Conservation Priorities

The Biodiversity Intactness Index is often used to assess whether ecosystems are intact to a healthy level - the WWF holds that you need over 90% intactness for a ‘resilient and functioning’ ecosystem. This 90% ‘threshold’ has been adopted across the scientific community in various forms, most prominently as a proposed planetary threshold on a global scale, but also to investigate temporal developments of biodiversity intactness at a national level. Biodiversity intactness can be calculated at any scale, so when you take a finer resolution, you can see the spatial variation in the extent of human impacts on the integrity of ecosystems.

Figure 1: The Biodiversity Intactness Index calculated for ‘pixels’ around the world (WWF 2022)

These differences (darker is more ‘pristine’, lighter is less) can be used to identify conservation priorities. For example, conservation projects that take place in areas with a higher level of biodiversity intactness are conserving ecosystems that are more ‘whole’ than projects in areas that have been heavily affected by human activity. The claim could therefore be made that these projects have a higher biodiversity co-benefit.

Identifying Restoration Opportunities

In addition to its use in the context of conservation prioritisation, the Biodiversity Intactness Index can also be used to see which areas have the most valuable restoration potential. These are areas with a low level of intactness, where human activity has severely degraded biodiversity in terms of species abundances. Carbon projects, by changing the way the land is used - for example through tree planting or natural regeneration - can have a greater positive impact in these areas than in areas where biodiversity is still largely intact.

Therefore, we are planning to include areas with a low Biodiversity Intactness Index in our biodiversity score as having greater potential for restoration. The dual use of the Biodiversity Intactness Index for the identification of conservation priorities and restoration potential mirrors what large-scale nature data providers are doing in the market (see for example the IBAT tools). Yet, the multi-scalar nature and workability of the Biodiversity Intactness Index makes it more flexible for us to include in our new biodiversity scoring. 

Temporal Insights and Project Trends

Another thing that makes the Biodiversity Intactness Index unique is its temporal dimension. The index can track changes over time, providing annual updates. AlliedOffsets displays this information for nature-based projects on our platform, for we have found it can accurately capture conservation (maintaining index position) and restoration (achieving significant increases in the index). 

Figure 2: Overview of our spatial data analysis dashboard

To test the temporal use of the Biodiversity Intactness Index, we ran the temporal dimension on a sample of just over 1,000 projects for the period between 2017 and 2020 (only using projects that started in 2017 or before). The majority of projects were quite stable, with 96% of the projects experiencing change of less than 5 percentage point, and 83% less than 1 percentage point. When significant changes occurred, they were roughly twice as likely to be negative than positive. These projects are both restoration and conservation projects, so they are not all meant to increase the size of the biospheric carbon sink, but it is concerning that a negative change in biodiversity intactness is more likely to occur than a positive change. 

This bias could partly be attributed to a more general decline in biodiversity intactness in ecosystems across the globe (particularly in tropical and subtropical ecosystems), with a myriad of different causes and spatial dimensions, so the extent of the ‘failure’ of some carbon projects to protect their ecological integrity is unclear. At the same time, there is evidence that ecosystem integrity can be effectively managed and increased when natural features are protected. That suggests that a significant portion of carbon market projects fail to protect the biodiversity that they are meant to conserve or increase.

Table 1: Number of projects experiencing change in Biodiversity Intactness Index (BII) for a representative nature-based carbon projects sample (n=1,826) in the period 2017-2020

There are some striking examples of the Biodiversity Intactness Index capturing the biodiversity value of projects. Take one of the Woodland Carbon Code (WCC) projects, “Coed Y Foel”, which started in 2017 and displayed a 14 percentage point increase in biodiversity intactness over the period between 2017 and 2020. The project takes place on abandoned pastureland, and includes a tree planting event that aims to restore broadleaf woodland, with a wide range of native species being planted. 

Figure 3: In Coed Y Foel, the planting includes Alder, Crab apple, Wild Cherry, Sessile Oak, Downy birch, Wych elm, Hazel, Hawthorn, Goat willow, Rowan and Holly (image credit: Stallion Valley)

Conclusion

The Biodiversity Intactness Index does not capture every element of biodiversity conservation and restoration potential. For example, it does not differentiate between the rarity or special value of certain species and ecosystems over others. This makes an increase in Biodiversity Intactness Index in the United Kingdom just as valuable as in a perceived biodiversity hotspot in tropical ecosystems. Still, this agnostic perspective makes the index usable on a global scale, especially since different designations of hotspots of biodiversity are often contradictory. 

In the absence of comprehensive and standardised on-the-ground monitoring of biodiversity in nature-based carbon market projects, adding the Biodiversity Intactness Index to our biodiversity product is an important step. We will be releasing more information on our updated biodiversity scoring system soon!