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NatureServe Conservation Status Assessments: Factors for Assessing Extinction Risk

Executive Summary

The primary purpose of Conservation Status Assessments is to evaluate the potential extinction or extirpation risk of elements of biodiversity, including regional extinction or extirpation. NatureServe and its member programs and collaborators use a suite of factors to assess the conservation status of species of plants, animals, and fungi, as well as ecosystems—ecological communities and systems. Conservation status is summarized as a series of ranks from “critically imperiled” to “secure,” and these ranks may be derived at global, national, or subnational (state/provincial) levels. This document details the NatureServe factors that are used to assess extinction risk.

NatureServe’s methods, which have been evolving since 1978, are used by its network of natural heritage programs and conservation data centers throughout North America. The NatureServe network compiles the data and information needed to assess extinction risk both subnationally and globally. In recent years, NatureServe has worked with the International Union for the Conservation of Nature (IUCN) to standardize the ratings for shared information fields, such as “Range Extent,” “Area of Occupancy,” “Population Size,” and “Threats.” This standardization permits the sharing of information between organizations and countries, and allows the information to be used in IUCN as well as NatureServe assessments. NatureServe has also developed a “rank calculator” to increase the repeatability and transparency of its ranking process. Ten status factors are grouped by rarity, threats, and trends categories, and information is recorded for each of the status factors, insofar as is possible. The rank calculator then computes a numeric score, based on weightings assigned to each factor and some conditional rules, which is translated to a calculated status rank. This calculated rank is reviewed and adjusted if deemed appropriate, with documentation of the reasons for adjustment, before it is recorded as the final assigned conservation status rank.

NatureServe conservation status assessment methodology contains a number of features, most notably that it:

  1. Considers all of the status factor data collectively in assigning a status;
  2. May produce “range-ranks” (e.g., G1G3 = globally critically imperiled to vulnerable) to transparently reveal the degree of uncertainty in a status when the available information does not permit a single status rank;
  3. Explicitly considers threats in the assessment;
  4. Assesses conservation status for both species and ecosystems; and
  5. Is sufficiently complete for North American species that global, national, and subnational ranks are routinely linked to facilitate setting conservation priorities.

 

Funding for the most recent revisions has been generously provided by the National Council for Air and Stream Improvement (NCASI), Office Depot, U.S. Fish and Wildlife Service, U.S. Forest Service, and the Sarah K. de Coizart Article TENTH Perpetual Charitable Trust.