A review of the index of biodiversity potential (IBP) as a tool for biodiversity evaluation in forest ecosystems

Following the Earth Summit in Rio de Janeiro (1992) and the Ministerial Conference in Helsinki (1993), a strong demand to increase biodiversity awareness among forest managers emerged. However, the comprehensive assessment of biodiversity in forest ecosystems is challenging due to the high number of taxonomic groups and species associated with forest ecosystems (WCFSD 1999). Furthermore, most forest managers do not have advanced skills in taxonomy beyond the identification of woody plants. To address this issue, several authors suggested adopting an indirect approach to biodiversity assessment. Fast forward to 2008, the Index of Biodiversity Potential (IBP) was created in France  (Larrieu and Gonin 2008) to address these challenges and overcome the limitations of routine forest biodiversity surveys by saving time and money. Thanks to ongoing financial support, the IBP has since been continuously improved by a research and development team, calibrated with taxonomic data and enhanced with an observer-effect assessment.

The IBP can be defined as an indirect, composite indicator designed to help forest managers implement the biodiversity conservation of forest-dwelling species in their day-to-day management. The IBP is a standardised methodology combining ten key factors for forest-dwelling species richness. Nine structural and compositional stand features are easily and directly recordable in the field by forest managers with no specialised taxonomic background other than the knowledge of tree species.  Three of them describe stand composition and structure (factors A, B, G); four describe old-growth features (factors C, D, E, F); and two describe non-tree-related habitats (factors I, “aquatic habitats”, and factor J, “rocky habitats”). The tenth factor assesses land- use history (factor H) and is mainly assessed in the office.  The ten factors provide complementary information, as they are only weakly correlated.

To assess these factors, the IBP has an integrated scoring system, by comparing threshold values with field observations recorded along a standardised itinerary inside the forest stand, a scoring system awards a score of 0, 1, 2 or 5 per factor. The global IBP score, i.e. the sum of scores for all ten factors, ranges from 0 to 50. Managers can then rank their stands along a gradient from low to high hosting potential for fungi, animal and plant species. The scores assigned to each factor are accompanied by an interpretation, which helps the manager to identify areas for improvement. The scoring system takes the local environmental conditions into account,  for example, by lowering the diameter at breast height and tree height thresholds in contexts particularly restrictive for tree growth, such as subalpine areas, the Mediterranean region or in sites characterised by very low soil fertility.

The IBP can be defined as a Biodiversity Evaluation Tool (Larsson 2001) since it includes factors focusing on structure (e.g. vertical structure of vegetation), composition (e.g. diversity of tree species) and functions (e.g. role of deadwood in nutrient cycling, complementation of resources provided by flower-rich areas), defined as key components of biodiversity in forest ecosystems  (Lindenmayer &  Franklin 2013). The IBP was deliberately designed to reflect an operational scale for day-to-day management.  Therefore, the IBP diagnosis is carried out at a local scale, within a homogeneous forest stand (a few dozen hectares at most). It therefore operates on the α-diversity level. Using stand-level IBP scores to determine a single IBP score for an entire forest massif is not appropriate. However, it is possible to use IBP scores to identify areas that are more or less favourable for forest-dwelling taxa, e.g. to optimise the location of set-aside conservation areas. The IBP undergoes regular updates to integrate advancements in knowledge and enhance its relevance and usability, while preserving continuity (e.g., maintaining the same set of factors) to ensure ease of use. Standardised version numbering and a table showing the changes made, and the correspondence between versions, make it easy to keep the diagnoses in context. The ten factors that make up the IBP were selected from a very large number of factors with a significant and positive influence on forest-dwelling communities (McElhinny et al.  2005), considering all forest-dwelling species, not just the rarest ones or those under a protected status. The selection was made so that any practitioner familiar with tree species identification can conduct the diagnosis without additional taxonomic knowledge. The way the factors are recorded was also simplified: the IBP focuses on the most relevant features in order to minimise field sampling efforts and focus on the most vulnerable aspects of biodiversity in managed forests, e.g. deadwood assessment is limited to the largest items. The standard IBP scoring is a  “capped” mode. In order to save time, forest managers stop observing a factor once the score of 5 points is obtained. This method takes  15–20  min per hectare in stands where walking is easy. Additionally, there is also an “uncapped” mode, which is further described in the article.

It is important to note that even though the IBP is designed for the assessment of individual stands and therefore only addresses α-diversity (i.e., variety of species within a single, defined ecosystem or habitat), information about the variability of the IBP on the landscape level or of a forest enterprise can be used to assess their ecological value. Recent studies suggest that structural heterogeneity at the landscape level is beneficial for biodiversity (Schall et al. 2020; Rothacher et al. 2025).

Over the years, in the development of the IBP, there has been a close collaboration between scientists and practitioners, supported by continuous funding for over fifteen years, resulting in a tool that is both scientifically relevant and adapted to field practice. In order to make the tool scientifically grounded, the IBP’s relevance for assessing biodiversity has been the subject of several studies, which are highlighted in the linked article.

Although the IBP tool is easy to use and accessible to anyone familiar with forestry issues, the speed and quality of the assessment depend on the observer’s experience. Acknowledging this, Gosselin & Larrieu (2020) assessed the observer effect on IBP scores. The main results were as follows, although the IBP can be measured throughout the year, attention should be paid to two factors, Native tree species (factor A) and Large standing deadwood (factor C), that showed a clear seasonal effect with some differences in the best season between factors (i.e. tree species are easier to recognize when they have leaves, while snags can be hidden by foliage in summer). Additionally, other factors also showed variability among observers, these were Flower-rich open areas (factor G), Vertical structure of the vegetation (factor  B). To reduce the variability in observed scores among observers, short two-day training courses tailored to the target audience  (professionals,  landowners,  decision-makers or teachers) and followed by a day of practice in the field are currently considered sufficient to master the IBP protocol. These trainings are important as prior research pointed out the importance of training to ensure quality recording of all the factors.

The IBP is designed as a rapid assessment tool to estimate the biodiversity potential of forest stands, but it has clearly defined limitations. It focuses on species diversity and does not assess genetic diversity, ecosystem functioning, naturalness, conservation value, or landscape-scale factors such as connectivity and historical influences. While IBP scores correlate with biodiversity patterns for several taxonomic groups, they should not be interpreted as direct measures of actual biodiversity or as mandatory management targets. Instead, the IBP is best used to identify forest features that support biodiversity and to guide management decisions, with higher scores indicating greater biodiversity potential rather than an absolute measure of ecological quality.

On the implementation side, many forest managers in France use the IBP to diagnose a stand before silvicultural operations or to evaluate the effect of harvesting on biodiversity. However, they are not alone. A broader range of actors also use the tool: natural area managers, including national and regional Natural Park officers, forest certification companies, teachers and researchers, local authorities,  etc. In general, the IBP is valuable for decision-making since its spatial scale matches the one commonly used by forest managers in their routine operations, i.e. the stand scale. A standardised spider diagram (see figure 7 in the article) facilitates creating biodiversity-friendly recommendations directly in the field,  following the diagnosis.

To support the use, a dedicated IBP website (https://www.cnpf.fr/ibp) provides free access to a wide range of resources, including documents and videos available in French and English. These materials help users to understand the IBP, select the best methods depending on context and objectives, conduct field assessments with practical field guides and sheets, and run training sessions. In addition, spreadsheets are available to archive data and edit standardised figures, and much more!

As a conclusion, the IBP is an innovative and rapid standardised habitat assessment method developed jointly by researchers and forest managers to help the latter apply integrative management in their day-to-day work. Kraus and Krumm (2013) defined integrative management as an approach that aims to integrate biodiversity conservation and adaptation to global change into forest management for the sustainable provision of multiple ecosystem services.  To our knowledge, the IBP has no equivalent to date. Since its scoring system is calibrated with taxonomic data and its observer effect quantified, this tool has now been fully recognised and is used in France by a wide range of people: forest managers, scientists, naturalists, funding bodies, and others. The IBP has been established as a useful tool for promoting integrative management in many forest contexts, from drafting management plans (stand ranking according to their potential biodiversity value, identifying and delimiting areas to be set aside, etc.) to stand diagnosis just before tree-marking operations (identifying stand features to be improved or conserved). It can also be used to address biodiversity conservation issues with forest owners who have little knowledge of forest ecosystems (educational tool) and to facilitate dialogue and negotiation between actors with divergent interests. Given that the relationships between the IBP and biodiversity as well as observer effects have been evaluated, that the IBP is sensitive to changes in stand characteristics, and finally that it is quick and easy to implement, the IBP could be used for rough monitoring of biodiversity over time. The experience gained in the last decade as the tool was adapted to a broad array of foreign countries should make it possible to easily adapt the IBP to European boreal forests as well as to temperate and boreal forests in North America. The IBP is currently being adapted or tested in 18 countries in Europe and the Mediterranean basin , creating a network of projects and organisations all focusing on developing biodiversity considerations in forest management.