THE invasive alien species (AIS) have become a global threat to many ecosystems. The world community is showing intense concern to the growing menace.

A number of international initiatives and coverage through conventions, treaties, governments, institutions, and guidelines have outlined thematic recommendations to address the issue.

However, in parts of Asia, the issue of IAS has low profile attention and priority because of a number of other priority concerns of stumbling socio-economic and political nature.

Under the auspices of the United Nations, Convention on Biological Diversity was adopted in 1992. In the recent years invasive alien species have become a serious problem and the international community has pledged to focus on this growing problem under global commitment to mitigate their harmful and adverse impacts.

Invasive Alien Species stand as the second largest threat to biodiversity. This binds 191 parties to the convention to “prevent the introduction of, control or eradicate those alien species, which threaten ecosystems, habitats or species.”

Invasive Alien Species, often called as exotic, non-native species, having arrived outside their natural distribution to areas where they easily invade ecosystems, marginalise several native species which brings about large scale environmental, ecological, and economic damage. According to an estimate, IAS has contributed to nearly 40 per cent of all animal extinctions since the 17th century. According to a study 10 per cent of the world vascular plants have the potential to invade other ecosystems affecting native biota.

The Chinese super-tree is listed as invasive species in many countries of the world. Similarly, Australian Eucalyptus and Acacias have profound effects on the local ecosystems. The species of Eucalyptus is environmentally least desired because of their leaf litter containing chemical compositions with the potential to restrict growth of species.

Introduced plant species grow fast, but it has been estimated that the damage caused by invasive species in terms of biodiversity loss and disruption of natural systems outweighs their benefits.

Beyond ecological repercussions, the problem of invasive alien species is multifold threatening agricultural productivity, forestry, fisheries, and natural systems. IAS have profound impact on economy by escalated control costs besides substantially damaging crop yield, forests, plantations, pastures, and the environment.

The impact of invasive species on biodiversity is increasing. Native to the Indian sub-continent, the ship rat (Rattus rattus) have caused extinction and decline of native birds on islands and have spread throughout the world. New disease organisms are proving fatal, such as avian influenza A (H5N1), attack humans and animals, in both temperate and tropical countries.

Biodiversity Action Plan for Pakistan also highlights the problem of invasiveness of flora and fauna. In Pakistan Eucalyptus camaldulensis has severe impacts on local ecology. In Malakand hills of NWFP, its dire impacts on the growth of grasses, herbs, and shrubs have been documented while almost eliminating associated species of scrub Dodonaea.

Studies indicate that in Pakistan 700 alien species are found, among these six species are considered to have extreme invasive nature, i.e. Broussonetia papyrifera, Prosopis juliflora, Eichhornia crassipes, Salvinia molesta, Parthenium hystrophorus, and Lantana camara. There is generally lack of awareness among nursery growers, general public, and even managers about the effects of these species.

Broussonetia papyrifera having East Asian origin is an invasive species in the Himalayas foothills which not only threatens natural vegetation of Islamabad and South Azad Jammu and Kashmir but has also become prime source of pollen allergy to about 46 per cent people of Islamabad. It was planted in 1960s in a bit to increase green cover. Prosopus juliflora has allelopathic effects which have replaced the native species in Sindh, irrigated plantation in Punjab and in tropical areas of NWFP.

Because of its toxic nature herbivores avoid the plant which also suppresses growth of indigenous plants. Its extended root bio-mass enables it to thrive through extreme climatic conditions of high temperatures and water scarcity. This adaptation predominate the native plants that are vulnerable to these extremes.

Similarly, Eucalyptus camaldulensis is also an aggressive invasive species in the mountainous areas and farm forestry. Besides their capacity of high water and nutrient intake, allelopathic effect, wind vulnerability, the tree has no fodder value and does not support nesting of birds. Lantana camara being native to the US is one of the 10 worst weeds of the world, has major appearance in Punjab affecting natural flora.

The Parthenium hystrophorus, originating in the Gulf of Mexico and Central South America was introduced in India which later invaded Pakistan is an aggressive weed in wastelands, road sides, water courses, and plantations. It can thrive well in high temperature zones; global warming scenario will even favour this invader.

Eradication of exotic species is timing and resource consuming. Being a global issue, IAS require international cooperation, cross sectoral collaboration, strengthening legislation regarding IAS, capacity building of staff, sate of the art initiative and techniques, checking cross boundary transit of IAS, inspection of shipments, mass awareness of major stakeholders, informed decisions, detailed scientific inventory, scientific research, and putting in place proper quarantine regulations. There is a dire need to abide by the CBD sets global priorities and guidelines and coordinate the international action on invasive alien species.

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