Alien flora of Pakistan: taxonomic composition, invasion status, geographic origin, introduction pathways, and ecological patterns

Inventories of alien species are important for monitoring and understanding the dynamics of invasion, which is crucial in devising management policies. The present study prepared a comprehensive inventory of alien plant species in Pakistan. Based on field observations, published work, scientific reports and online databases, 400 alien taxa were identified (83 families, 265 genera), 180 of which were classified as casual alien, 117 as naturalized, and 103 as invasive. Poaceae (61 taxa) and Asteraceae (46 taxa) were the richest families, while Ipomoea (9), Amaranthus (8) and Euphorbia (8) were the genera with the largest numbers of alien taxa. The greater majority of alien species were annuals (32%) irrespective of their stage in the process of invasion. Alien species from all continents have invaded Pakistan but the primary donors of alien species are Temperate Asia (176) and Africa (143 species). Alien taxa inhabit all six geographic regions of Pakistan and the largest number (117) is found on the Punjab fertile plains. Ruderal habitats support a wide array of alien plant species, hosting almost all the alien species irrespective of their invasion status. The introduction pathway of the great majority of alien species remains unclear (67%) due to insufficient data on their history of introduction. Our account of the alien flora of Pakistan draws attention to further work needed and highlights the gaps that need to be addressed for devising a national alien species management strategy.