http://dawn.com/2011/03/28/invasive-pla ... diversity/
Many non-native plants have been introduced into new territories, initially as either ornamental plants or for erosion control, stock feed, or forestry. Whether an exotic will become an invasive species is seldom understood in the beginning, and many non-native ornamentals languish for years before suddenly naturalizing and becoming invasive.
Japanese knotweed grows profusely in many nations. Human beings introduced it into many places in the 19th century. It cost the UK government in excess of 7 million pounds to remove it from the site of the Olympic games in London. With Pakistan’s socio and economic problems I would find it hard to believe such an investment would ever be made. The origin of the devastating alga in the Mediterranean was thought by many to be an accidental introduction from an aquarium. 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. 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, it is a major pest in the 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.
In addition purebred naturally evolved region specific wild species can be seriously threatened with extinction through the process of genetic pollution i.e. uncontrolled hybridization] introgression and genetic swamping which leads to homogenization or replacement of local genotypess as a result of either a numerical and/or fitnesss advantage of introduced plant or animals. Nonnative species can bring about a form of extinction of native plants and animals by hybridization and introgression either through purposeful introduction by humans or through habitat modification, bringing previously isolated species into contact. These phenomena can be especially detrimental for rare species coming into contact with more abundant ones where the abundant ones can interbreed with them swamping the entire rarer gene pool creating hybrids thus driving the entire original purebred native stock to complete extinction. Attention has to be focused on the extent of this under appreciated problem that is not always apparent from morphological (outward appearance) observations alone. Some degree of gene flow may be a normal, evolutionarily constructive process, and all constellations of genes and genotypes cannot be preserved however, hybridization with or without introgression may, nevertheless, threaten a rare species' existence.
Pakistan may have some very lax border and import controls but it should be our own moral and social duty to preserve our own environment and biodiversity. We should all be conscious of the effects of our actions lest we lose some of our own beautiful and native flora.
Please don’t take this the wrong way as the purpose of including this information is not to criticise but to educate as to the proven factual effects of some our seemingly innocent actions.
regards
Ifzal
