Element Occurrence Ranks

Ecology Contents

About CDC Ecology Ranking Methology Element Occurrence Ranking Element Occurrence Ranks Element Occurrence Ranking Factors Element Occurrence Specifications Spatial Patterns

Basic EO ranks used in prioritizing EOs for conservation planning purposes are shown in the table below.

The basic “A” through “D” ranks are based on currently known factors that are used to estimate the viability of an EO. The more viable an EO is, the higher its EO rank and the higher its conservation value.

Whenever possible, EOs should be assigned ranks according to criteria specified for “A”, “B”, “C”, and “D”-ranked occurrences. This includes EOs for native Elements that have been reintroduced,as well as exotic Elements (those with Element rank = “SE” or “NE”, or those that are locally exotic) that are critical to the survival of the species. When evidence of presence is lacking, or when field information is not sufficient to assign an “A”, “B”, “C”, or “D” rank, the other basic ranks, “E”, “H”, “F”, or “X” may be used.

The “E” = EXTANT EO rank should be used for an EO that has been recently verified as still existing, but sufficient information on the factors used to estimate viability of the EO has not yet been obtained. Use of the “E” rank should be reserved for those situations where the occurrence is thought to be extant, but an “A”, “B”, “C”, “D”, or range rank cannot be assigned.

The “H” = HISTORICAL EO rank should be used when there is a lack of recent field information verifying the continued existence of an EO, such as:
a) when an EO is based only on historical collections data; or
b) when an EO was ranked “A”, “B”, “C”, “D”, or “E” at one time and is later, without field survey work, considered to be possibly extirpated due to general habitat loss or degradation of the environment in the area.

This definition of the “H” rank is dependent on an interpretation of what constitutes “recent” field information. In general, if there is no known survey of an animal EO within the last 20 years, it should be assigned an “H” rank. Similarly, if there is no known survey of a plant or community EO within the last 20 to 40 years, it should be assigned an “H” rank. While these time frames represent suggested maximum limits, the actual time period for historical EOs may vary according to the biology of the Element and the specific landscape context of each occurrence (including anthropogenic alteration of the environment). Thus, an “H” rank may be assigned to an EO before the maximum time frames have lapsed. Occurrences that have not been surveyed for periods exceeding these time frames should not be ranked “A”, “B”, “C”, or “D”.

The higher maximum limit for plants and communities (i.e., ranging from 20 to 40 years) is based upon the assumption that occurrences of these Elements generally have the potential to persist at a given location for longer periods of time. This greater potential is a reflection of plant biology and community dynamics. However, landscape factors must also be considered. Thus, areas with more anthropogenic impacts on the environment (e.g., development) will be at the lower end of the range, and less-impacted areas will be at the higher end.

The “F” = FAILED TO FIND EO rank should be assigned to an EO that has not been found despite a search by an experienced observer at a time and under conditions appropriate for the Element at a location where it was previously reported, but that still might be confirmed to exist at that location with additional field survey efforts. For EOs with vague locational information, the search must include areas of appropriate habitat within the range of locational uncertainty. An “F” rank, when applicable, supersedes an “A”, “B”, “C”, “D”, “E”, or “H” rank.

The “X” = EXTIRPATED EO rank should be assigned to an EO for which there is documented destruction of its habitat or environment, or persuasive evidence of its eradication based on adequate survey (i.e., thorough or repeated survey efforts by one or more experienced observers at times and under conditions appropriate for the Element at that location).

Source: Draft Element Occurrence Data Standard