Prosopis julifora, locally known as devi or velayati keekar. – File Photo

KARACHI: Invasive plant species are a major threat to country's indigenous biodiversity for they are fast replacing local vegetation, it emerged on Sunday. Dawn

While speaking to , some senior botanists warned the authorities against planting of alien species on a large scale unless their impact on the environment was scientifically studied.

They said that Conocarpus plantation on a large scale in Karachi was not a well-thought-out action on part of the city district government, because the plant had properties that were damaging for local biodiversity.

According to the experts, mesquite, commonly called velayati keekar or devi (Prosopis julifora), among the alien species, has been proved to be a real menace for local biodiversity as it releases harmful chemicals that have extreme negative effects on the growth and survival of other plants.

Prosopis julifora, a shrub native to Mexico, South America and the Caribbean, has spread across Pakistan, including Kashmir, over the decades. In fact, it invaded every town and became dominant by eliminating natural vegetation, they said.

“Its 'success' can be attributed to its allelopathic properties.

This means that the plant releases certain inhibitory chemicals into the environment where it affects the development of neighbouring plants,” said Dr Mohammad Qaiser, a botanist and vice chancellor of the Federal Urdu University of Arts, Science and Technology.

The toxic chemicals, he said, were found in all its parts except bean pods which were eaten by animals. “The animal couldn't digest the seed which are excreted through droppings. They germinate in suitable conditions and develop deep roots to tap underground water,” he added.

He said the plant should be replaced with indigenous species as the former contaminated the soil with its toxic effects. But this was not an easy task because the invasive plant could regenerate even from a little piece of roots left in the soil, he added.

Invasive plants could thrive in areas beyond their natural range of dispersal, as the species were hardy with high adaptability and reproductive capacity and could cause harm to environment and humans, he said.

Prosopis julifora was first introduced before the partition and later by the forest department on a large scale. This helped the species to naturalise in the environment, Dr Qaiser said.

Referring to the International Union for Conservation of Nature (IUCN), he said that the organisation had listed mesquite plants of the Prosopis genus as one of the world's most problematic invasive species along with an aquatic plant, Eichornia crassipes.

Prosopis julifora did have some uses but its disadvantages outweigh its benefits, he said.

Another species of the same family found in Pakistan was Prosopis glandulosa. The other alien invasive species harming local vegetation include Parthnium hysterophorus (found in the Punjab and Khyber-Pakhtunkhwa), Broussenetia papyrifera, salvinia and eucalyptus species.

Speaking of certain negative impacts of some invasive species, Dr Qaiser said that Broussenetia papyrifera (paper mulberry) was the cause of pollen allergy in Islamabad while eucalyptus was known to lower water table under the soil. Pistia stratiotes, Eichornia crassipes and Salvinia species were aquatic plants and now widely cover water bodies after destroying local vegetation.

Sharing his opinion on the subject, Dr Ajmal Khan, who heads the Institute of Sustainable Halophyte Utilisation at Karachi University, said: “Invasive species might not be problematic in their native environment because of nature's controlling mechanism in specific ecological conditions that help maintain their population at a certain level.

“Their peculiar characteristics combined with a lack of natural enemies often leads to outbreak populations.

This is the point we must understand when we think of introducing an exotic species.”

The government, he said, must not plant alien species on a large scale unless their impact on the environment was scientifically studied. Besides, there was a need to create awareness about the harmful effects of exotic species on local biodiversity so that people refrain from bringing in seeds and saplings of exotic species, he added.

“The planting of Conocarpus species on a large scale in Karachi by the city district government was also not a well-thought move as the plant has similar properties as that of Prosopis julifora,” Dr Khan concluded.