Streamlining alien species listing processes to enable prioritisation and reporting in protected areas: The case of alien plants in South African National Parks

Management of alien species is a critical conservation priority in protected areas. Reliable alien species checklists are central to prioritisation, early detection, long-term monitoring and reporting. Yet, methods vary widely, from structured field surveys with herbarium vouchers to data aggregated from online platforms, atlases, citizen science and scientific journal publications. These sources often use inconsistent naming systems, especially where alien species names differ between the introduced and native range. We describe the processes used over three decades by South African National Parks to compile alien species lists, highlight key shortcomings and propose a ten-step process to improve checklist development. Our approach generates a dynamic occurrence database that integrates static historical datasets with dynamic sources, such as iNaturalist, from which up-to-date checklists can be produced. Central to this process is taxonomic standardisation against a taxonomic backbone, combined with annotations of identification certainty and spatial accuracy and the assignment of unique record and taxon identifiers. Applying this process across parks yielded a consolidated list of 1,330 unique taxa – significantly longer than previous versions. The increase reflects broader scope (e.g. inclusion of 206 extralimital taxa) and incorporation of new data streams, while some park lists shortened due to removal of misidentified or synonymous taxa. Around one-third of alien species recorded were absent from the national checklist, underscoring the need for a systematic approach to alien species listing. As conservation indicators increasingly depend on such lists, we recommend explicit guidance is provided on: (1) classifying invasion status and stage, especially for cultivated species; (2) treatment of extralimital aliens; and (3) verification standards for non-expert or spatially imprecise records. Using our proposed process alongside such guidelines will provide a robust foundation for consistent alien plant species reporting in protected areas, strengthening the value and application of alien species lists.