Species Habitat Index
Visuals and Presentations
Metadata
WCMC | CBD metadata webinar presentation - 4 Mar, 2022
Overview
The integrity of ecosystems is broadly defined by the status of their component species and the ecological processes they support and require. Integrity can be assessed by the degree of change (loss and gain) in the set of species and associated processes observed within an ecosystem and its habitats. The Species Habitat Index (SHI) measures this change and captures alterations in the ecological intactness of ecosystems.
The index measures changes in the estimated size, connectivity and quality of species habitats. The index uses species as core units of analysis, thereby capturing the individual ecological processes associated with species that are central to ecosystem integrity. The index uses spatially explicit information at a resolution of single pixels such as 1 km2 to support aggregate measures of the ecological integrity of defined geographic units (landscapes, seascapes, mountains, regions, and country). Given the species-level nature of the metric, SHI informs about trends in species population size, distribution, health, and, as proxy, genetic diversity.
Metrics
The SHI is calculated and validated using species occurrence data combined with environmental change data informed by remote sensing. Calculations use best-possible predictions of species geographic distributions (Species Populations EBVs), based on a variety of sources combined with species habitat information. The SHI can be calculated by parties with national data, such as national biodiversity monitoring data or land-cover classifications. A full suite of annual country-level indicator values and extensive species-level data and metadata supporting it are made available through GEO BON, and parties can readily use these directly for their reporting or use it to augment their own calculations.
Species level maps and trends: For each species, change in two metrics is assessed for a point in time relative to the baseline period:
- Size of suitable habitat (Area; in km2): This is given by the product of summed suitability (continuous range of 0 – 1) of individual landscape pixels and their size. For suitability expressed in binary form (presence-absence maps) for 1 km2 pixel, this is simply the total presence pixel count.
- Connectivity of suitable habitat (Connectivity; in km). As basic measure this is given as the average distance to edge of suitable area across all suitable pixels, a widely-used, robust measure of connectivity (GISfrag metric). For custom calculations at national level this can be extended to include other information, e.g. measures that weight the distance among habitats by the resistance to movement of the intervening landscape.
A combined species-level SHI metric is given as the average species Area and Connectivity at a given point in time compared to the reference period. For example, a 4% and 6% decrease in Area and Connectivity, respectively, would result in species-level SHI = 95 (average between 96 for Area and 94 for Connectivity) compared to a baseline SHI = 100. Note that the previous version of SHI used just the Area component. An assessment of both the Area and Connectivity components of SHI is urged, and an alternative SHI formulation could use the minimum rather than average of these two components to provide an even more sensitive metric of ecological change.
Country level measurement: The SHI of a geographic unit is given as the mean of SHI values of the species in that unit, at a given point in time. SHI values for a country can either be computed as simple mean across species (National SHI) or by weighting species-level values by the proportion of the global population the country is estimated to hold (Steward’s SHI). In addition to reporting on the separate Area or Connectivity aspects of SHI, indicator subsets can address different species groups, e.g. species dependent on certain habitats and ecosystems, rare or threatened species, or those with particularly rapid recent habitat changes.