NatureServe Conservation Status Assessments: Factors for Evaluating Species and Ecosystem Risk

Larry Master

Primary Goal: To assess the conservation status of species and ecosystems—specifically the extinction risk of species and elimination risk of ecosystems at global scales, and their extirpation risk at national and subnational (e.g., state, province, territory) scales—using standard methods. NatureServe and its network program staff across North America collect and evaluate data for species and ecosystems of concern using these methods and tools to ensure that assigned status ranks are accurate and consistent, based on current field and remote sensing information.

Rank Factors (described in the document)

  • Eight core status rank factors are identified as relevant to risk assessments of extinction/elimination, or extirpation
  • Descriptions of each factor include the basis for its use, and its evaluation and rating criteria


  • Factors are organized into three categories (rarity, threats, trends)
  • Conditional rules for use of factors are applied to ensure that adequate information is used for assessing status
  • Factors are scaled and weighted according to their impact on risk
  • Consistent factor scaling and weighting allows the use of points to effectively score the contribution of each factor to risk
  • Scores are weighted and combined by category resulting in an overall calculated rank, which is reviewed, and a final conservation status rank assigned


  • A rank calculator automates the process of assigning conservation status ranks
  • NatureServe’s Biotics database provides management for all conservation status information

NatureServe and its member programs and collaborators use a suite of factors to assess the conservation status (extinction or extirpation risk) of species of plants, animals, and fungi, as well as the conservation status (elimination or extirpation risk) of 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 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 World Conservation Union (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 both 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, in so far as 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 (ecological communities and systems); and (5) is sufficiently complete for North American species that global, national, and subnational ranks are routinely linked to facilitate conservation priority-setting.

NatureServe Author(s)


  • Master L, Faber-Langendoen D, Bittman R, Hammerson GA, Heidel B, Ramsay L, Snow K, Teucher A, and Tomaino A. 2012. NatureServe Conservation Status Assessments: Factors for Evaluating Species and Ecosystem Risk. NatureServe, Arlington, VA.