Even though legumes, grasses and orchids are relatively well-known taxonomically and may be broadly representative of plant diversity, the task of assessing trends in the status of approximately 50
000 species is a major challenge. The current IUCN Red List (Baillie et al. 2004
) includes approximately 12
000 plant species of which ca.
000 were added in the past year. Not all of the assessments submitted to date have been processed: resources in the IUCN/SSC Red List Programme Office are a significant limiting factor in the system. A fivefold increase in the rate of production of assessments is required in order to have even these groups fully assessed by 2010. This will require significant additional resources both to enable the generation of assessments by specialists and to allow the results to be processed and incorporated in the database. And, if achieved, this would yield just a snapshot of current status for these groups, a single point for each species rather than the minimum of three data points per species needed to detect a change in rate of loss over time. However, there is potential to obtain preliminary trend data using a combination of existing data, Geographical Information Systems (GIS) and modelling techniques.
The herbaria of the world are extraordinary repositories of data on the distribution of plant species through space and time. For instance, each of the approximately 7 million specimens in the Kew herbarium documents the presence of a particular plant species at a particular point in space and time. There is growing recognition of how such data can be integrated with environmental spatial data in order to document and predict spatial patterns of biological diversity (Graham et al. 2004
). Specifically, herbarium data can be used to provide the information on which IUCN Red List assessments can be based.
Plotting distribution maps based on specimen data is a long-established practice among taxonomists, but new approaches using GIS have the potential to offer tremendous added value (Willis et al. 2003
). In particular, it is possible to use macros developed by one of us (J. Moat) to automate the measurements of geographical range that are used in IUCN assessments (http://www.redlist.org/info/categories_criteria2001.html
). Herbarium data can be used to make evaluations based largely on criterion B—small range, defined in terms of extent of occurrence or area of occupancy, combined with estimates of fragmentation, continuing decline and/or fluctuation, and also on criterion D—population with a very restricted area of occupancy or number of locations (see Butchart et al. 2005
; Schatz 2002
; Willis et al. 2003
). Given a series of plotted distribution points, both extent of occurrence and area of occupancy can be easily calculated and two alternative approaches have been implemented to allow assessment of the number of subpopulations and fragmentation of the population (Willis et al. 2003
A drawback of this approach, because it focuses primarily on criterion B, is the possibility of underestimating extinction risk by overlooking species that might be listed if data were available to use criteria A, C or D. However, as a method of generating preliminary assessments for subsequent verification by experts and/or fieldwork, the approach is a useful starting point and a promising shortcut. Among the plant species on the current Red List, assessments based on criterion B predominate (e.g. Oldfield et al. 1998
). GIS-based methods are now being applied to generate preliminary assessments of the conservation status of species being treated for floras and monographs or described as new to science. Currently, at the Royal Botanic Gardens, Kew and the Missouri Botanical Garden, they are applied to hundreds of species per year and are expected to be extended to thousands of species over the next few years. The techniques could just as easily be applied to tens of thousands of species given sufficient distribution data in appropriately geo-referenced form. The limiting factor is the rate of conversion of relevant specimen label data into electronic records suitable for GIS analysis.
Converting the information held in the world's herbaria into electronic form has long been recognized as an important but challenging task. In many cases, type holdings have been prioritized for databasing (and often for imaging), since they are especially valuable to taxonomists. There are also logistical advantages to selecting types based on the way that herbaria are commonly organized. However, there is an equally valid argument to prioritize databasing of label data from specimens of species most likely to be of conservation concern, so that assessments of conservation status can be based on all of the available information. However, in the absence of a complete listing of species of conservation concern, how can we construct a sample of herbarium material that is as rich as possible in specimens of these species?
Du Puy et al. (2002)
monographed the legumes of Madagascar and undertook assessments of the conservation status of all woody endemic species. The specimen database developed during the course of this study includes all relevant material from herbaria, with significant holdings from Madagascar (including Kew, Missouri and Paris), and is believed to include the vast majority of the world's herbarium collections for these taxa. The database includes 8932 specimen records for 435 endemic species (woody and herbaceous). Of these, 228 species can be considered to be of conservation concern (CR, EN, VU and NT) when assessed using the GIS routines described above (see ). Almost half (49%) of all the species surveyed were represented by 10 specimens or fewer, and these accounted for 82% of the species that were ultimately assessed as being of conservation concern. Most strikingly, these specimens comprise just 11% of all the specimens databased. In other words, if all species of Malagasy endemic legumes represented by no more than 10 specimens in the world's herbaria had been assessed, the greatly reduced investment in capturing label data would still have enabled specimen-based assessments for almost half of the endemic species, including the majority (82%) of species that can be established by this method to be of conservation concern. A threshold of 20 specimens per species would have captured information to support conservation assessments for 69% of the endemic species, including 96% of those provisionally rated as being of conservation concern. This result could have been achieved by capturing label data for just 26% of the available specimens. Species represented by more than 40 specimens accounted for more than half of the investment in specimen data capture, but not one of these was rated as of conservation concern. While these data have value in increasing the representation of species of Least Concern, there are clearly efficiencies to be achieved by gathering full datasets for just a few of such well-represented species.
Percentage representation of endemic Madagascar legumes plotted against number of specimens per species, n.
Madagascar is extraordinary in its levels of endemism and, perhaps, unusual in the degree to which its collections are concentrated in a few major herbaria. However, the same general pattern is also seen in other areas of the world (e.g. Western Cameroon; M. Cheek & G. Gosline, unpublished data). The same pattern is also seen in the numbers of specimens available for species already on the Red List. A random sample of 100 vascular plant species from the 2003 Red List included 62 species represented in the Kew herbarium. Of these, 74% (46) were represented by no more than 10 specimens. A collaboration between the Royal Botanic Gardens, Kew, the Missouri Botanical Garden and New York Botanical Garden is now exploring how these patterns can be further understood and exploited to help maximize the efficiency with which herbarium specimen data are captured for conservation purposes and to identify, and where possible quantify, any biases which may be inherent in this approach (A. Paton, E. Nic Lughadha, R. E. Magill, B. Thiers, K. Harman, M. Tulig & C. Ulloa, unpublished data). Rarity in the herbarium does not always correlate with rarity in the field, but specimen numbers and specimen-based distributions are the best readily available indicator of relative rarity that we have at our disposal and, as such, the best basis for large-scale preliminary conservation assessments.
Automated GIS-based approaches do not produce authoritative conservation status assessments ready for submission to IUCN for inclusion in the Red List, but they do produce useful preliminary conservation assessments that allow efficient screening of many hundreds of species. Species that appear most likely to be of conservation concern can then be assessed by specialists using additional information, such as knowledge of the ecological requirements of particular species and/or remote sensing data on the extent and quality of habitats, to provide as complete as possible a picture of the current conservation status of the species. Of course, it is essential to ensure that a proportion of these specimen-based ‘desk’ assessments are ground-truthed. Conservation status assessment exercises of this kind are best concentrated in areas where they are supported by extensive field experience and/or active networks of in-country collaborators. To apply such an approach, at anything beyond a local scale, will require the coordinated effort of many institutions and individuals.