KARACHI, Aug 11: The decision of planting eucalyptuses in large numbers has adversely affected the biodiversity of the city.

Environmentalists point out that eucalyptuses, which are known as safaida in common parlance, are allelopathic; that is to say, they inhibit the growth of other plants by the action of substances they release.

Early this year the federal government banned the plantation of eucalyptuses in forests citing the harmful effect that the plant has on the environment.

Native to Australia, eucalyptuses are a very fast-growing plant which can grow up to 326 feet in height. In The gardener, author A.K. Khan writes: “Many species and varieties [of eucalyptuses] are under cultivation in Australia. It is the tallest tree used in ship-building... The leaves are lemon scented and the trunk is white.”

Environmental biologist Prof Dr M. Ajmal Khan said he had always opposed the idea of planting foreign plants in the local habitat. “Experience shows that, when planted in a new habitat, most foreign plants die out. Those which manage to survive cause a great deal of harm to the eco-system, developed over hundreds of years. They also pose a threat to the animals which otherwise lead a harmonious existence with native plants.”

Dr Khan cited the example of prosopis juliflora, commonly known as Babool. “There are many theories about the advent of prosopis juliflora in the local habitat. Some say that it came into the region in the fodder for the horses of British soldiers. Others insist that Ayub Khan got the seeds of the plant from abroad. In any case, it is a well-known fact that the seeds of the plant, native to western North America, were sprayed in Balochistan. It was then argued that being a sand-binder plant it stopped sand from being blown away. As a result, it has spread extensively in Karachi, where under-ground water is very close to the surface. Since the roots of prosopis juliflora are very deep, they can tap water and survive easily, even if the city receive no rains.”

He recalls that some 30 years ago, there were more than 550 species of wild plants native to Karachi. He regrets that most of them have vanished, thanks to contrived changes in the biodiversity of the city.

When contacted, Sindh forest secretary Shamsul Haq Memon told Dawn that plantation of eucalyptuses had also been banned in the province. He said: “Five years ago, the government had planted about 100,000 eucalyptuses in Karachi. Since the roots of the plant go very deep, they damaged water pipelines and sewerages in a big way.”

He added that eucalyptuses had been introduced in Pakistan to tackle the problem of salinity and water-logging. “When the water crisis became acute in the country, it was pointed out that eucalyptuses wasted a lot of water. It was then decided that the plantation of eucalyptuses should be stopped,” he said.

Dr M. Ajmal Khan, however, contended that the effect of eucalyptuses over salinity was exaggerated. “It is a fallacy that eucalyptuses reduce salinity of land. Since they are not halophytes — and thus unable to grow in saline conditions — they can do little against salinity. Able to evaporate water fast, they can reduce water-logging to a certain extent.”

The chairman of the botany department in the University of Karachi, Qaiser Mahmood, who is also editor of prestigious The flora of Pakistan, said that the number of flying foxes — large fruit bats with a foxlike face, found in Madagascar, South-East Asia and northern Australia — had increased in Karachi. “These birds love to feed on eucalyptus flowers. They fly long distances looking for eucalyptuses. When they do not find eucalyptus anywhere, they destroy other plants and orchards,” he explained.

He said that eucalyptuses had their advantages as well. For instance, they could be planted in barren, water-logged land, he said, adding that the demerits of the plant outnumbered its merits.

The director of the coastal eco-system department at IUCN, Tahir Qureishi, recalled that the government had got eucalyptuses from Australia in the late 1950s and the early 1960s. “It was decided that eucalyptuses would be used for the paper and the pulp industry. While the government planted eucalyptuses in large numbers, it failed to develop the industry for it simultaneously. This flawed approach of the foresters of the country is responsible for the plantation of eucalyptus in large numbers,” he said.

Mr Qureishi said that eucalyptuses were most unsuitable for avenue plantation. He said that they should be eradicated from urban areas and in their place other trees be planted.