KARACHI: Stop growing exotic species and make the plantation more diverse, suggested Dr Zafar Iqbal Shams during his lecture on urban forestry held at the Garden Centre on Saturday.

The event was organised by the Horticulture Society of Pakistan on its premises.

Giving a presentation on the subject, Dr Shams, senior Karachi University teacher with a doctorate in environmental sciences, said that it was important to know the definition of a tree that go to a certain height and develop a canopy.

“Besides being an exotic species with harmful effects on the environment, the conocarpus (a North American species) grown extensively in the city is a shrub and not a tree,” he added.

“What we need to address is the increasing levels of pollution, traffic noise and urban heat by planting a large number of native trees,” he said, adding that the ecosystem services of an urban forest to dwellers were huge.

Sharing findings of his study that showed a comparison between the composition and diversity of plantation existed in 1993 and 2013 along the 15-kilometre-long Corridor-1 (starting from Merewether Tower and ending at Sohrab Goth), he said that he prepared a plant inventory of this route on the request of Karachi Mass Transit Project officials in 1993.

Later, he revisited the data in 2013 and found that plant diversity had greatly reduced with an increased number of exotic species.

“The species diversity index had declined from 8.74 in 1999 to 1.4 to 2013. This is dangerous as a single plant infected with a disease could affect all trees and you would lose all your investment,” he explained to the audience.

The urban forestry rule, according to him, states that not more than 10pc trees of any species should be planted, not more than 20pc trees of any genus should be planted and not more than 30pc trees of any family should be planted.

On native species versus exotic species, he said that the study also showed that the corridor heavily comprised conocarpus species (84pc). Earlier in 1993, there was not only a better composition of native and exotic species, but there were more trees and less shrubs as well.

“In 1993, there were 2,198 shrubs and 2,212 trees whereas in 2013 there were 8,780 shrubs and 756 trees. The species diversity in 1993 was greater than 11 US cities,” he said, while showing slides with lists of exotic and native species found during the study.

Trees, he pointed out, should be studied first along with consultation with experts from civic agencies operating in a particular area where the species was to be planted in order to avoid future problems.

He recommended plantation of local ficus species that he said were easy to grow and required little water.

During the question-answer session, it was pointed out that moringa, native to parts of Africa and Asia (locally called sohanjana ki phali), was a miracle tree with immense health benefits and should be planted in the city on a wider scale.

The species was rich in calcium and protein. Its leaves could be used for making herbal tea while the seed oil could be used to have a glowing look, a participant informed the attendees.

It was also said that Karachi was fast expanding and the government, after consulting academic and civic experts, should make it mandatory for builders to plant certain species on the land before handing it over to people.

Published in Dawn, August 30th, 2015

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