SHARE

Urban tree branches and even entire trees often fall on roads damaging property. But it makes the news only when such an incident results in casualties A Bo tree in the Family Health Bureau premises recently fell damaging several buildings, although no casualties were reported. Revered though it maybe, Bo is still a fig. Due to the religious affiliations figs are considered sacred whether it is a Bo tree, a Nuga or what is colloquially referred to as Kaputu Bo, where saplings that sprout out of seeds propagated by crows. But the figs are also a threat that is virtually strangling urban tree population.

Threat
In fact figs are taking over urban trees at an alarming rate. In her paper Figs (Ficus spp.) dispel the splendour of Colombo Streets – a case Study (2012) and an unpublished report submitted to the CMC on problematic fig growth on street trees in Colombo 7, Colombo University, Head of Plant Sciences Department, Dr. Sudheera Ranwala explains the fig effect. It starts with a tiny fig seedling sprouting in the fork of another tree. The seedling sends roots snaking down the trunk. In stage two the fig grows wrapping its roots around the host tree all the way to the ground. In stage three the roots almost completely envelop the base of the host tree, ultimately killing the host tree and leaving a giant fig in its place.

Among the figs found in Sri Lanka, only few show epiphytic characteristics. Such fig species include Gas netol/Wal ehetu (Ficus tinctoria ssp. Parasitica), Banyan tree (Ficus benghalensis), Rubber (Ficus elastic) and Bo (Ficus religiosa). All species except Bo strangle their hosts.

Research has found that of the 850 street trees observed in the Colombo 7 area, 145 (17 percent) were invaded by figs. Sixty percent of the affected host street trees were Kaha Mara (Peltophorum pterocarpum). The others were Para Mara (Albizia saman – 25 percent) and   Andara (Pithecellobium dulce – five percent). For the purpose of their paper Evaluation of Tree Health and Safety of Urban trees in Colombo, for International Urban Conference on ‘Cities, People and Places; Towards a new urbanity’ (2015) Dr. Ranwala and co-author Pramodi Hewavitharana investigated some 47 wards within the Colombo City limits over a period of three to four years. Over a 1000 street trees were profiled for two studies conducted between 1956 to 2010 and 2010 to 2016. Not only was their health analyzed, but threats posed by these trees were also identified. In their studies Dr. Sudheera and Hewavitharana deduced the percentage of trees with bulging roots damaging pavements.

City dwellers
Street trees can also pose considerable threats to city dwellers when the canopy becomes saturated during rain, explained Sudheera. “Rain soaked branches can break off and fall damaging property and even lives.” Trees have to be pruned so as not to block the view of oncoming vehicles, she said. “But this has to be done in consultation with an expert,” stressed Ranwala. She warned that an inappropriately pruned tree could cause more danger than an overgrown one.

“Since most of the city surfaces are paved the soil underneath is compact, consequently city tree roots extend over a very limited area,” explained Ranwala. “This is clearly visible when trees are uprooted. The root system is often a bulging mass.” The extension of the root system is restricted and the tree cannot hold or balance its weight.

“You have to be particularly careful when pruning fig trees,” explained Ranwala. Prop roots of figs are often clipped by Colombo Municipal Council workers oblivious to the fact that such root systems are the fig’s mechanism for maintaining its mass in balance. “Doing so tips the tree’s balance,” opined Ranwala. She further said that people are often reluctant to cut fig trees, even when they clearly pose a threat, because of religious beliefs.
The tree near Sirimavo Bandaranaike Girls School is of particular focus because it prevents the clear view of oncoming traffic, said Ranwala. Roots that bulge through the pavement force pedestrians to use the road. Figs are permitted in open spaces but not on pavements.”

Strategic beautification
Ranwala reiterated the significance of seeking expert advice when planning urban landscapes. “For example any expert would recommend that no species should exceed ten percent of the total population,” said Ranwala. In lay terms it means that every species should represent less than ten percent of all the trees planted in a given area, thereby encouraging more diversity. “Authorities should plant more of species that are scant,” he pointed out.

Ranwala noted out that such planning should be a collaborative effort of Urban Development Authority, Central Environmental Authority, Police Environment Unit and the Colombo Municipal Council.

“Universities pay millions on free education, it seems such a waste that authorities are not using our research and making use of their invaluable data,” said Ranwala, adding that the Colombo University Plant Sciences Department is more than ready to comply if such a request was made. “A similar consultancy would cost six to seven hundred thousand in the private sector and the universities are willing to do it free of charge,” he added.

“All attempts to beautify our cities will fail unless public participation is encouraged,” said Colombo University, Head of Plant Science Department, Dr. Sudheera Ranwala. “General public should be encouraged to take interest in presenting their views on street and park trees,” she opined adding that city dwellers should co-operate with relevant authorities in making their own individual contribution to this common goal. “The authorities should be able to consider the requests by residents regarding pruning, removal of parts if trees that pose danger to their private property.

 

  • Garawi

    Yes,I too notices this fact of banyan trees taking over creating danger to the host. It seems that unlike in the west, no city council in this country has a department that monitors the health of trees in the cities by cutting off unnecessary branches and make sure the city trees are healthy. Current governments environment ministry should seriously think about this!