Alien and invasive plant species of the Indus Delta.
Floristic survey of the Indus delta was conducted over ten years from 2001 to 2011. During this work, 31 alien or non-native species were collected for the first time from the study area, of which three species, viz. Prosopis juliflora, Salvinia molesta, and Eichhornia crassipes were found to be highly invasive; the first one in the terrestrial habitats and later two in freshwater to brackish aquatic ecosystems. Another 3 species were also found to be invasive, while 10 showed tendency to become invasive in future. Invasive species are recognized as a big threat to the native biodiversity. They also create many other environmental problems and even threaten the health of human beings and livestock. A comparison with the old records showed that the number of alien species has steadily increased in the recent decades. Before the present work, only 25 alien or non-native species were known from the study area and none of them was invasive. The total number of alien species is now 56. The factors responsible for the spread and establishment of alien species include increased and faster human travel, increased international trade, and destruction, fragmentation, or modification of the natural habitats. The current global climatic change may be another contributing factor in the future; therefore an effective strategy is needed to check further import and establishment of alien species.