For. Snow Landsc. Res. 75, 3: 293–302 (2000) 293 Interpreting the IUCN Red List categories and criteria for cryptogams Nick G. Hodgetts Joint Nature Conservation Committee, Monkstone House, City Road, Peterborough, PE1 1JY, UK [email protected] Abstract In 1994 the World Conservation Union (IUCN) published revised Red List categories, with criteria and guidelines on how they should be used. While this a substantial improvement on the previous system, it was clear that it had to be interpreted in different ways for differernt taxonomic groups. In particular, assigning threat categories to lesser-known groups such as cryptogams and invert- ebrates required the criteria to be interpreted in an appropriate way. This led the European Committee for the Conservation of Bryophytes (ECCB) to produce guidelines on interpreting the categories specifically for bryophytes. The numerical thresholds in the IUCN publication appar- ently require much quantitative data. Since these sorts of data are rare for bryophytes, evaluation against the threat categories must often be done by inference from what data are available. The most relevant data that can be used for bryophytes are population decline, present distribution and total population size, number of sites, and estimated loss of habitats over a specified period of time. It is thought that the guidelines developed for bryophytes may be applicable to a wide range of cryptogams, including lichens, perhaps with some modification.The revised IUCN categories have been applied with some success to lichens in Great Britain. Keywords: IUCN, Red List, cryptogams, criteria, bryophytes, lichens 1 Introduction Red Data Books (RDBs) and Red Lists are very useful tools and sources of information for use in species conservation. The original system of threat categories proposed by the World Conservation Union (IUCN) has been used widely throughout the world. In 1994, the IUCN produced a revision of the Red List categories,along with criteria for assigning them to species (World Conservation Union 1994). This revised system provided the means to assess species status much more objectively than was possible before, using a series of numerical thresholds based on measurements of abundance and decline. PALMER et al. (1997) described how the revised system was being applied in Britain and HALLINGBÄCK et al. (1998) showed how it could be used for bryophytes.The latter paper has now been adopted semi-officially by IUCN as a recommendation for the use of the system for bryophytes. 294 Nick G. Hodgetts 2 The IUCN Red List categories and criteria The old IUCN categories have been fully explained elsewhere (IUCN Threatened Plants Committee Secretariat 1981; PALMER et al. 1997), so are not repeated here. In summary, the old Red List categories are Extinct,Endangered,Vulnerable and Rare,with the further categor- ies Indeterminate, Insufficiently known, Out of danger, Not threatened and No information. Although used extensively, this system was subjective and non-quantitative. The revised IUCN categories (World Conservation Union 1994) seek to provide a more objective method for determining the degree of threat to species.The Red List categories are Extinct, Extinct in the Wild, Critically Endangered, Endangered and Vulnerable, with the further categories L ower Risk (divided into three subcategories: conservation dependent, near threatened and least concern), Data Deficient and Not Evaluated. These categories are summarised in Figure 1.The criteria used to place taxa within the categories are summarised in Table 1. Extinct (EX) Extinct in the wild (EW) Ye s Critically endangered (CR) Extinct? Endangered (EN) Ye s No Vulnerable (VU) Threatened Adequate Ye s data? Threatened? Ye s No No Conservation dependent (cd) Evaluated? Data deficient (DD) Near threatened (nt) No Nationally Scarce (ns) Least Concern (lc) Lower risk (LR) Not evaluated (NE) Fig. 1. Hierarchical relationships of the categories. IUCN definition of Extinct (EX): “A taxon is Extinct when there is no reasonable doubt that the last individual has died”. IUCN definition of Extinct in the Wild (EW): “A taxon is Extinct in the Wild when it is known only to survive in cultivation,in captivity or as a naturalised population (or populations) well outside the past range”. The application of this system to plants (including lichens) in Britain is explained by PALMER et al. (1997).The system is complex and offers a range of alternatives for identifying the status of threatened species.A species is required to fulfil a minimum of one criterion (of criteria A to E) to qualify for the Red List. Species are tested against all criteria, working “downwards” through the threat categories (starting with Extinct) until the appropriate cat- egory for that species is found.The species is allocated to the “highest” category that it fits. In other words, if a species is determined as Critically Endangered using criterion B but only Endangered using criterion C, its status is Critically Endangered. Decline may be measured directly as a reduction in the number of “individuals” observed or, in the absence of this infor- mation, inferred from habitat or distribution data. For. Snow Landsc. Res. 75, 3 (2000) 295 Table 1. Summary of the thresholds of the IUCN Criteria. criterion main thresholds Critically Endangered Endangered Vulnerable A. Rapid decline >80% over 10 yrs or >50% over 10 yrs or >20% over 10 yrs or 3 generations in past 3 generations in past 3 generations in past or future or future or future B. Small Range – extent of occurrence extent of occurrence extent of occurrence fragmented, declining <100 km2 or area <5000 km2 or area 20 000 km2 or area of or fluctuating of occupancy <10 km2 of occupancy <500 km2 occupancy <2000 km2 C. Small population <250 mature individuals, <2500 mature individuals, <10 000 mature and declining population declining population declining individuals, population declining D1. Very small <50 mature individuals <250 mature individuals <1000 mature individuals population D2. Very small range <100 km2 or <5 locations E. Probability >50% within 5 years >20% within 20 years >10% within 100 years of extinction 3 Interpretation of the categories and criteria for cryptogams The revised IUCN system has now been used in Britain in published Red Data Books for lichens (CHURCH et al. 1996), vascular plants (WIGGINTON 1999) and bryophytes (CHURCH et al. 2001). With use, it is clear that the system can be used for these organisms and that it is a considerable improvement on the old system. However, it has to be interpreted appropri- ately according to the taxonomic group to which it is applied. The following guidelines give an indication of how the criteria may be interpreted for lichens, using as a basis the British lichen Red Data Book (RDB; CHURCH et al. 1996) and the guidelines produced by the European Committee for the Conservation of Bryophytes (ECCB), primarily for the purposes of making a European bryophyte Red List (HALLINGBÄCK et al. 1998). Note in particular that: – the IUCN criteria need relatively little “interpretation” in order to work effectively; – the concept of “extent of occurrence” is not used, as it is usually meanlingless for lichens and bryophytes in the present context; – these guidelines must be used in conjunction with the official IUCN Red List categories (World Conservation Union 1994). Extinct (EX) Not having been seen in the wild in Britain during the last 50 years, despite searches having been made, and not maintained in cultivation (CHURCH et al. 1996). Taxa for which all known localities have been checked repeatedly in the last 30 years without success, or taxa listed as extinct or vanished in all available Red Lists, if the total area of distribution is covered by Red Lists (HALLINGBÄCK et al. 1998). 296 Nick G. Hodgetts Note: 1. No distinction has been made between EX and EW for cryptogams. As in the old system, the IUCN definition of Extinct is open to considerable interpretation. Critically Endangered (CR), Endangered (EN), Vulnerable (VU) (IUCN criteria A to D are indicated. Criterion E was not used, as it requires a population viability analysis, which is normally not available for lichens or bryophytes) A . L arge decline Major population decline observed, estimated, inferred or suspected in the last 10 years, or three generations, whichever is the longer: 80% decline = CR 50% decline = EN 20% decline = VU Notes: 1. The subcriteria for this criterion listed in the IUCN guidelines allow decline to be inferred from distributional information, habitat degradation/decline or the effects of pollutants. 2. Generation time is a useful concept for cryptogams, as it enables decline over a longer time period than ten years to be used in assessing Red List status. However, it is an area that needs more work from lichenologists. Advice for bryologists (HALLINGBÄCK et al. 1998) has been to use a maximum of 25 years for one generation (i.e. for species that are not known to reproduce sexually), with a “sliding scale” of 11–25 years for species that reproduce sexually only infrequently,down to 1–5 years for short-lived ephemeral colonists that reproduce frequently with small, highly mobile spores. In other words, a system of life strategies, such as that devised by DURING (1992) for bryophytes, needs to be adopted in order to obtain a broad estimate of generation time. B. Restricted area of occupancy, few localities, decline To qualify under this criterion, a species must occupy a restricted area and have few localities