The IUCN Red List of Ecosystems (RLE) is an emerging global standard for ecosystem risk assessment. The RLE, much like the NatureServe Conservation Status and South African assessments, integrates data and knowledge to document the relative risk status of ecosystem types. In order to determine at-risk status, types must be classified, described, and mapped. A series of measures are then applied to assess trends in ecosystem extent, the relative restricted nature of its distribution, and the relative severity of environmental degradation and disruption of biotic processes. For IUCN, all measures aim to gauge the risk of range-wide ecosystem “collapse.” Ecosystems are assigned to categories of Collapsed (CO), Critically Endangered (CR), Endangered (EN), Vulnerable (VU), Near Threatened (NT), Least Concern (LC), Data Deficient (DD), or Not Evaluated (NE). Collectively, CR, EN, and VU types are considered “threatened” ecosystems. Comparable categories exist in NatureServe and South African methods.
The approach to ecosystem classification and the level of thematic resolution (i.e., broad-scale vs. fine-scale types) interact with assessment criteria, affecting risk assessment outcomes. By standardizing classifications used in risk assessment processes in North America and South Africa to a) the vegetation-based hierarchy of the EcoVeg approach, and b) the proposed IUCN Ecosystem Functional Groups, we can identify key effects of classification approach and thematic resolution on risk assessment outcomes.
Results/Conclusions
Several levels of thematic detail are reflected in the ecosystem classifications used for risk assessment. Classification units assessed in North America (n=640) approximate levels 6 (group) and 7 (alliance) of the EcoVeg hierarchy and represent 36 Ecological Functional Groups. Classification units assessed in South Africa (n=458) approximate levels 5 (macrogroup) and 6 (group) of the EcoVeg hierarchy and 17 Ecological Functional Groups.
When ecosystem types are defined at finer levels of thematic resolution (e.g., level 6 and below), a greater proportion of types are assigned to threatened categories. This is primarily because pressures on ecosystem types are more pervasive across the distribution of more narrowly defined types (e.g., at group and below) than for more biophysically heterogeneous types (e.g., at macrogroup and above). However, available data on distribution and condition become increasingly limited with finer classification levels.
In applying at-risk criteria to standardized classifications, we provide one important focus for governments and civil society to prioritize conservation effort. However, users of ecosystem risk assessment systems should be aware of the implications of classification approach and thematic detail on risk assessment outcomes.