IUCN threat categories primarily assess the probability of the species becoming globally extinct owing to its small population size or high population decline rate. The threat categories have been frequently revised by the Species Survival Commission (SSC) group of the IUCN for application to several macroscopic organisms. Latest IUCN red listing i.e. 2000 system recognizes three threatened categories reflecting different population growth rates.
1. Critically Endangered (CR)
2. Endangered (EN)
3. Vulnerable (VU)

Other categories of conservation concern, but not threatened are:

1. Near Threatened (NT) [Akin to Conservation Dependent in earlier version, where deliberate conservation measures are needed to prevent the taxon from meeting the threatened criteria.]
2. Least Concern (LC) [i.e. Low Risk as in earlier version, which doesn't mean that the species can stand neglect or over-exploitation, it's just that it is not immediately prone to extinction.]

1. Extinct in the wild (EX-W) when only captive breeding under ex situ conditions is possible.
2. Extinct globally (EX).
3. Data deficient (DD), which does not mean that the species is not threatened, but that the threat can be judged only after collection of adequate data.
4. Not evaluated (NE) includes several species that were not evaluated primarily because those were too abundant to be of foreseeable conservation concern.

IUCN Threat Criteria
Each of these threat categories can be deduced based on any one of the five criteria that reflect extinction risk:

1. Declining population (past or projected): This includes species with high harvests, especially in destructive fashion. Eg: Rauvolfia serpentina
2. Narrow distribution, fragmentation and decline or fluctuation: Several endemic species prima facie appear to be natural candidates for qualifying as threatened as per this criterion. Eg: Cyas beddomei
3. Small population size and decline: Absolute population number low and rate of decline high.
4. Very small population or very restricted distribution: Absolute population numbers/ expanse extremely meagre.
5. Quantitative analysis of probability of extinction: simulations using deterministic and stochastic population models.

The five quantitative criteria aim at detecting risk factors across a broad range of organisms and the diverse life histories they exhibit. The quantitative values in each criterion were developed through consultation, but there also exists modest formal justification for these values. Meeting any one of these five criteria qualifies a taxon (species or lower e.g. variety) for listing at that level of threat. If a taxon meets two or more threat criteria/categories, the higher risk status and corresponding risk criteria is accepted. For, being inactive given the lower threat status on one criterion exposes the species to extinction due to the other criterion. Although the criteria for each of the threat categories are based on quantitative thresholds such as enumeration or observation, inference such as from records of habitat area decline or projection such as growing market demand etc. are permitted. Thus, the taxa for which there exists very little population information can also be assessed, using IUCN criteria and their participatory application in Conservation Assessment and Management (CAMP) workshops.

Why rapid methods for threat assessment are needed?

To promote red listing in the tropics by overcoming the lacunae of data, Conservation of Breeding Specialist Group (CBSG) of the IUCN has developed a participatory rapid threat assessment method that synthesizes the first hand and even unpublished perceptions of direct or indirect resource users such as botanists, traders, forest officials. This method relies on a workshop to bring together the resource users. These Conservation Assessment and Management Plan (CAMP) workshops detect threat levels, their causes and corrective management options for highly traded and endemic species.

How much work has been done so far on threat status of Indian Medicinal Plants?

Globally, about 10 percent of the known flowering plants are threatened with extinction. Similar estimates have been made for India also. In comparison with the magnitude of possibly threatened species of medicinal plants only preliminary work on identifying threatened species has been initiated. Since the rapid methods are not perfect, they do provide the first indications of threat. To focus on threat assessment for medical plants the Foundation for Revitalization of Local Health Traditions (FRLHT), Bangalore and CBSG-India are working jointly. FRLHT has facilitated six rapid assessment workshops in peninsular India during 1995-2001. The results include separate assessments for five states- Maharashtra, Andhra pradesh, Karnataka, Kerala, and Tamil Nadu, besides a consolidated, regional assessment for the latter three states i.e. southern India together. These six workshops covering five states were held at Bangalore (4), Pune (1) and Hyderabad (1) in the winter season (January to March) each year during 1995-2001. Over 200 experts including from BSI, forest official, industry employees, healers shared their views in these workshops.

In each of these workshops about 50 species were assessed, totalling to 161 unique species, as many (assessed) species were common across workshops, for reassessment or sub-regional assessment. Species endemic to Peninsular India (72) accounted for 40 percent of species assessed while majority of the species had less than 5 percent of their global population occurring in the region. Herbs (25 percent) and climbers (28 percent) each accounted for a quarter of the species assessed, while trees (44 percent) accounted for nearly a half, as these are in lower population sizes, regenerate far less and more susceptible to destructive practices such as de-barking or lopping.

Besides these peninsular Indian workshops, FRLHT facilitated a workshop for high elevation Himalayan plants from Jammu & Kashmir and Himachal Pradesh states, where 34 of the 42 species assessed were found threatened. Zoo Outreach Organization, Coimbatore also facilitated CAMP workshops at Lucknow that assessed 75 species of northern India of which 69 were found threatened.

Why species become threatened?

Over harvesting from wild is the reason for becoming threatened in the case of specific species that are traded in high volumes. Habitat loss and fragmentation affect over three fourths of the threatened species. Habitat degradation can be compensated through eco-restoration only if habitats have not been irreversibly lost. However, harvests, especially destructive practices can be minimized by regulations, providing much-needed breathing space for the threatened species populations to gradually restore. This is necessary as 90 percent of the raw material worth Rs.120 million used by the Indian herbal industry is today entirely harvested from the wild. Commercial cultivation to ease pressure on wild stock is presently not lucrative, as harvests from the wild are both available and much cheaper.

Limitations of IUCN categories and rapid assessment methods

The IUCN red listing has been used extensively both globally and in many countries for many taxa. However, IUCN categories reflect only relative extinction risks, ignoring many values often used for conservation prioritisation e.g. utility values, ecosystem functions, taxonomic distinctiveness, endemism and feasibility, though some of these are indirectly reflected in choice of species to be assessed by IUCN methodology. Ideally, a threat assessment methodology should also value intrinsic (pollination, dispersal modes and other reproductive bottlenecks, germination and survival rates etc.) factors that differentially affect different species exposed to same level of extrinsic threat (habitat loss, destructive harvest etc.). However, data relating to intrinsic threats are almost non-existent or very sketchy for most tropical species, including Indian. An inevitable limitation of IUCN methodology is that different species assigned to a single threat category may be susceptible to different intrinsic threats. For instance, amidst all species belonging to `vulnerable' category dioecious species such as many Ficus species are more threatened than monoecious species that dominate most genera. For, the former require higher population where fewer trees produce female flowers and fruits and self-pollination is impossible, being dependent on wasps.

A theoretical limitation of CAMP approach has been the emphasis on subjectivity of data coupled with attempt for consensus, which departs from the usual scientific practices that benefit from objectivity and divergence. While departure from mainstream is scientifically progressive, successful management needs social consensus rather than conflict, as attempted in the CAMP process. The CAMP version earlier excessively emphasized on quantifying threat level, besides over-emphasis on captive breeding recommendations. However, the revised Taxon data sheet (TDS) format overcomes this lacuna both by eliciting suggestions for in-situ management and making ex-situ conservation recommendations based less on genetics and more on purpose.

Red Listed Plants identified so far

Rapid threat assessment exercises carried out for 'some' of the species of conservation concern in southern and northern India, as per latest IUCN guidelines, have brought to notice around 200 medicinal plant species are under various degrees of threat. These exercises have not yet assessed all the species that are of conservation concern. It is estimated based on global rates of plant species threatened with extinction that around 1000 medicinal plant species may be under threat in different eco-systems across India. No threat assessment exercises for medicinal plants have how ever been carried out so far for central, western, eastern and north-eastern states.