Scientist urges city hall to plan tree-planting

By Joseph Bernard A. Marzan

An Ilonggo scientist on Friday, May 17, advised the Iloilo City government to carefully consider the plants it grows in public spaces, warning that poor choices could harm the environment and be costly.

Dr. Resurreccion Sadaba, a biology professor at the University of the Philippines Visayas (UPV), acknowledged the city government’s consideration of native trees that do not buttress into concrete features in center islands and sidewalks.

City General Services Office (GSO) chief Neil Ravena said on Monday, May 13, that they were leaning towards the dita or bita tree (Alstonia scholaris) due to its crown and potential to avoid buttressing.

Buttressing occurs when a tree’s roots grow uncontrollably, rising to the soil level and sometimes destroying the concrete boundaries or barriers around it.

Sadaba said that, like all other trees, the dita tree will buttress as it ages. While the city does not need to worry about this now, it will need to be monitored in the future.

He added that another important consideration is the leaves, noting that large-leaved trees can provide more shade in the bike lanes while shrubs can be planted on the middle island.

“For many [trees], at around [50 to 80 years], it will start to develop buttress roots. […] We might not be alive when the trees buttress and may destroy the concrete. [The proposal] is a bit tricky,” Sadaba told Daily Guardian on Air.

“Even the Talisay [trees] we have, the older ones, they become really big when you let them be. With that small of an area, it may conquer the space and destroy it when the time comes,” he added.

Sadaba, who has extensive experience in mangrove conservation and coastal fisheries resources protection, said that the city government must also consider where they are planting trees.

The royal palm trees and pink trumpet trees planted along the center island and the mixed-use “bike lanes” of Benigno Aquino Jr. Avenue (Diversion Road) are considered invasive alien plant species (IAPS), being native to the United States and Cuba, and El Salvador, respectively.

IAPS, which refers to plants not native to the areas where they grow, can cause major damage if not managed properly.

A 2020 article by Indian scientists Prabhat Rai and J.S. Singh listed risks posed by IAPS in non-native habitats, including habitat destruction, land use change, and biotic invasions. These impacts ultimately affect environmental quality, increase risks to human health, threaten socio-economic security, and accelerate local climate change.

Sadaba cited the Ateneo de Iloilo in Mandurriao district as a good example of considering the immediate environment, where the school community has planted native mangroves in beach forest areas.

He suggested that the city government consider medium-sized tree species, which may also be drought-resistant, including members of the Fabaceae (legume) family.

He also emphasized the need to consider public policy on road safety.

“One thing about their choice to use palms in the center island is because they just grow tall [without obstruction]. But in terms of shade, they do not have any purpose. […] [They can also do] shrubs because these can also be drought-resistant,” he said.

“[Some of the trees on General Luna Street] have already obstructed [and] pose a safety hazard to road users. That is why they need to take a long time to consider factors before they act,” he added.

While the dita tree is good as a native tree, Sadaba said that what the city needs for Aquino Avenue is shade for pedestrians and cyclists using the paths.

He noted Singapore’s vision in the 1960s to become a ‘garden city’, and how the trees planted back then still benefit residents and tourists to this day.

“Dita trees provide less shade because they have smaller leaves. What is better is that they need trees that provide shade to the people passing by. The Talisay tree is actually good because it is low-maintenance and grows fast,” he remarked.

Iloilo City Mayor Jerry Treñas recently announced plans to replace the royal palm and pink trumpet trees with native and exotic trees, along with retrofitting works to make the plant boxes deeper.

Sadaba was one of the experts Ravena mentioned advising the city government on their greening activities.

Other experts include landscape architect Paulo Alcazaren, Dr. Jurgenne Primavera of the Zoological Society of London-Philippines, and retired prosecutor Jeremy Bionat.