Generales

By Sergio Alejandro Ruiz Saldarriaga, Journalist at UdeA Communications Office 

Trees do much more than provide shade and oxygen. Researchers at UdeA examined six tree species with unique abilities to resist pollution, clean the air, and indicate air quality conditions in Medellín. They analyzed leaves from key locations to inform urban planning and tree-planting efforts. These findings support strategies to ease the city’s environmental stress. One of the standout species is the mango tree!

Researchers have studied 25 of the 750 tree species found in the Aburrá Valley. Photo: Courtesy of UdeA Communications Office / Alejandra Uribe F. 

Forests often evoke images of peace, harmony, and clean air. In a busy city like Medellín, it’s easy to overlook how much a single tree can contribute. Researchers at the Environmental School of the Faculty of Engineering at Universidad de Antioquia have spent years studying this topic. They’ve focused on the tree species that thrive in the city and pinpointed the areas where their presence makes a significant difference. 

“Trees function as natural filters, capturing and removing atmospheric pollutants that harm health and the ecosystem,” said Mauricio Correa Ochoa, professor and researcher at G-Lima, a research group at the Environmental School. 

Professor Correa has contributed to air quality research for over 10 years. Since 2018, as part of his doctoral thesis, he has led a project that gathers air pollution data from the Early Warning System stations in Medellín and the Aburrá Valley (Siata). 

Her research, titled “Evaluation of the Air Pollution Tolerance Index and the Expected Performance Index of Six Tree Species in an Urban Tropical Valley: Medellín, Colombia,” draws on the tree inventory of the Metropolitan Area of the Aburrá Valley, which lists around 750 species. This inventory guided the selection and location of the species studied, with additional consideration given to the pollution levels recorded by the 22 air quality stations in the region. 

The research concentrated on four stations, selected for their high pollution levels, located near the Antioquia Museum, the National University, the Jaime Isaza Cadavid Polytechnic, and Tanques La Ye. Within a 500-meter radius of these stations, researchers assessed 54 adult trees from six common species: mango, pink guayacán, búcaro, gualanday, African tulip tree, and urapán. 

The World Health Organization suggests that cities should have one tree for every three residents to improve air quality. Photo: Courtesy of Grupo G-Lima. 

The study measured four key parameters from the leaves collected and processed in the lab: ascorbic acid, moisture content, pH, and total chlorophyll. Researchers used these measurements to calculate the Air Pollution Tolerance Index (APTI) and the Anticipated Performance Index (API), which classify species as sensitive or tolerant to pollution. 

“Some trees are sensitive, becoming sick and stressed, which shows in their leaves. It is how we began identifying and classifying resistant species that could help purify the air,” Correa Ochoa explained. He pointed out that the most significant signs of stress include leaf discoloration, deformation, and pest infestations. 

The research involved sampling at specific times and days, determined by the study’s cost and travel distances. Later in the project, technology-enabled on-site chlorophyll measurement. 

They resist, purify, and monitor air quality. 

These plants produce oxygen, enhance spaces, and convert CO2 into biomass, helping to clean the air. It is crucial in urban areas, where the accumulation of particulate matter quietly threatens public health. 

Mango (Mangifera indica) was one of the most pollution-tolerant species in the study. “Mango trees remain stable in both polluted and clean air conditions. They’ve been the most resilient species we’ve identified in this research,” said Correa Ochoa. 

The researcher noted that, although the mango tree isn’t native, it offers many benefits: it provides shade, helps regulate temperature, produces edible fruit, and tolerates high pollution levels in Medellín. 

In contrast, pink guayacán (Tabebuia chrysantha - rosea) was the most sensitive species, showing physiological stress and poor performance in highly polluted areas. 

The study also categorized búcaro (Erythrina fusca) and gualanday (Jacaranda mimosifolia) as highly sensitive species. These trees function as bioindicators when positioned in key locations for ongoing monitoring. 

The African tulip (Spathodea campanulata) and urapán (Fraxinus uhdei) were classified as intermediate-level species, making them suitable for mixed and strategic urban planning. 

Smart planting: UdeA’s dual strategy

The Aburrá Valley is believed to be home to approximately one million tree species, according to population estimates. Photo: Courtesy of UdeA Communications Office / Alejandra Uribe F. 

Currently, the entities in charge of environmental decision-making in the city have fundamental but valuable information, as the Aburrá Valley lacks detailed tree species studies. “This is a key opportunity to prioritize these studies, which provide vital data for informed decision-making,” the sanitary engineer noted. 

The Aburrá Valley is short of more than 350,000 trees, worsening the environmental crisis and fueling annual pollution spikes. 

The study suggests that tree-planting decisions should prioritize ecological factors as well as aesthetic ones. It advocates for a mixed strategy, combining pollution-tolerant trees to mitigate pollution with sensitive species that act as ongoing indicators of environmental degradation. 

“The priority is to identify areas with high pollution, choose locations for tree planting, and adjust the infrastructure—such as pavement, clay bricks, tiles, and buildings,” concluded Correa Ochoa.