KARACHI: The exotic Conocarpus heavily dominates streets of Karachi, which exhibits extremely low flora diversity with exotic species outnumbering native ones. Several major streets do not have any trees at all while countless trees have been uprooted for redevelopment of urban infrastructure over the years, says a Karachi University (KU) study recently published in an international journal.

Titled Town socio-economic status and road width determine street tree density, the study is published in the Urban Forestry and Urban Greening.

Led by their research supervisor, Dr Zafar Iqbal Shams, six students of the Institute of Environmental Studies collected the data during 2016-17. They were: Mubah Shahid, Zara Nadeem, Shafaq Naz, Dania Raheel, Darakshan Aftab, Tayyab Raza Fraz and Muhammad Sohaib Roomi.

An important initiative in recent years, the research based on the data collected from 18 (defunct) towns of Karachi provides detailed information about the species planted along streets, its relation with the socio-economic status of residents, as well as gaps in the government approach towards city’s plantation.

According to the study, there is a lack of appreciation and dearth of knowledge regarding street trees in Karachi despite growing importance and understanding about urban forestry.

Of the total 62 species found here, 54 have less than one per cent presence

“Karachi exhibits low species diversity mainly due to repeated planting of one or few species on its streets over the years. Overreliance on a few species could be a potential threat of their complete elimination from the streets due to diseases, pests or environmental changes.”

Overall, the study recorded 62 species (30 native and 32 exotic) along city’s streets. Of them, the proportion of 54 species, many of which were native, was less than one per cent.

The street tree community, according to the study, had 62 per cent plants of Conocarpus, demonstrating its dominance on the streets.

Top five species recorded were; Conocarpus, lignum, neem, white fig and eucalyptus.

The study also found that the towns of high-income residents demonstrated high tree density compared to those of low-income residents.

The study attributed this pattern to high land value, better infrastructure of roads and sidewalks in high-income areas and lack of interest by relevant civic agency in plantation in low-income areas.

Some towns of low-income residents, Orangi, Baldia and Korangi, however, were found to have greater species richness.

“The civic agency generally removes all the trees, while planting one or two species of its choice. For that reason, Orangi Town had the highest species diversity and one of the lowest tree densities.

“Lyari, a town of lowest-income residents, had the lowest tree density and one of the lowest species diversities, which shows lack of appreciation of street trees by both the agency and local residents.

“Moreover, the town lacks wide verges and spacious median on its streets, which could be one of the reasons of low tree planting.”

Some affluent towns demonstrated very low species diversity, mainly due to monoculture planting on their streets. For instance, Gulshan-i- Iqbal demonstrated low species diversity.

“The town accounted for 75 per cent trees of Conocarpus in its street tree community. Low species diversity in street tree community is one of the most serious management issues that show its over-reliance on merely a few species,” the study says.

The study found that species’ diversity on the streets of Karachi is lower than that of 22 US cities and the towns of Eastern Cape, South Africa.

Highlighting the strong presence of exotic species on Karachi’s streets, the study refers to some other researches and states that these species are less suitable for planting in an urban area compared to native species, which support significantly greater diversity and density of avifauna than those of exotic species.

The exotic species listed by the study include curtain fig, rusty fig, prosopis juliflora (keekar), Leucaena leucocephala (jantar), royal palm, cassia tree, jelly bean tree, copper pod, rubber plant Pithecellobium dulce (jangle jalebi), Delonix regia (gul mohar), tamarind (imli) and Morus nigra (shahtoot).

The native species include date palm, pink siris, peepal, bamboo, coconut, banyan tree, moringa, barn, amaltas and jangli badam.

Don’t kill Conocarpus

Asked how city’s street tree cover could be improved, Dr Shams recommended an end to monoculture plantation — a very common trend for the last few decades on Karachi’s streets.

“Decades ago lignum was monocultured on the streets followed by eucalyptus and then conocarpus from 2005 to 2015. The recent study shows that 62 per cent of street trees are of conocarpus species, which is an over-representation of a single species,” he said.

However, Dr Shams strongly rejected the idea of uprooting a single tree of Conocarpus, arguing that there were a lot of vacant spaces, particularly in low-income areas of the city, where trees of other species could be planted.

“As the study shows that the proportion of some 54 species was less than one per cent, we should try to grow more of these plants after carrying out soil survey, consultation with some ecologists and community engagement to ensure their long-term wellbeing,” he said.

The number of these species, he pointed out, should be increased which would naturally decrease the proportion of Conocarpus, which is not an invasive species,” he suggested.

According to Dr Shams, the city cannot afford to remove all the exotic species as its tree cover is already very thin.

“In the urban forestry nowadays, exotic species are not an issue but rather the invasive species — the ones which spread and replace other species without human assistance and are extremely dangerous for local flora. For instance, keekar and jantar,” he said, adding that all exotic species were not invasive.

The Conocarpus like eucalyptus improve soil conditions in waterlogged areas and could be planted after a thorough land survey, he said.

Published in Dawn, December 29th, 2019