Extent of occurrence and area of occupancy of tallow tree (Sapium sebiferum): using the red list criteria for documenting invasive species expanse.
Invasion by exotic species is a prime threat to biodiversity and information on their expanse is pivotal for effective management of bioresources, with this perception we worked out the extent of occurrence (EOO) and area of occupancy (AOO) of Sapium sebiferum (L.) Roxb. in the Himalayan state of Himachal Pradesh (HP), as is done for IUCN plant threat categorization. Three methods namely aerographic method (AM), cartographic method (CM) and cartographic method by conglomerates (CMC) were deployed and compared for the same in the geographic information system environment. As expected, the three results varied amongst themselves, with AOO being 1127.58, 4046.00 and 734.12 sq km for AM, CM and CMC, respectively. On the other hand the EOO was 4,091.44 sq km. This is a considerable expanse and amounts to more than 7% of the total geographical area of HP. Based on field surveys and observations, CMC was found to give the most reliable estimates. Though, primarily devised by IUCN for threat categorization of native species, we feel that EOO and AOO may appropriately be applied to invasive species also.