Invasive weeds of southern districts of Khyber Pakhtunkhwa-Pakistan.
Invasive weeds are one of the greatest threats to the local biodiversity as invasive weeds reduce the abundance and diversity of native flora and fauna and adversely affect ecosystem processes. Once alien weeds become established in a new region, they are extremely difficult to manage. Therefore, need an urgent and pro-active development of early preventative plans including early detection of alien species, their population size, residence time, number of introduction attempts, ecology, seed spread mechanisms, previously documented invasions and evaluation of similar types of species and possible cost effective management methods. In this regard, an attempt was made to identify invasive weeds in the southern part of Khyber Pakhtunkhwa, conducting a survey in four southern districts i.e. Bannu, Lakki Marwat, Tank and Dera Ismail Khan, during March 2002 to September 2003. Among the total of 50 problematic weeds 12 weeds were reported as highly invasive. These were Avena fatua, Carthamus oxyacantha, Prosopis juliflora, Conyza bonariensis, Eucalyptus camaldulensis, Phragmites austrailis, Xanthium strumarium, Galium aparine, Asphodelus tenuifolius, Amaranthus viridis, Imperata cylindrica and Trianthema portulacastrum. Among these Prosopis juliflora and E. camaldulensis were purposely introduced, while rest of the species were introduced accidentally or were present in the local flora, but due to ecotypic changes these became aggressive, invasive and suppressed the local flora. Therefore, proactive plan of weed management is required through prevention of new introductions, vigilant detection of new populations and constant efforts to manage the worst invaders.