In the diverse landscapes of Mexico, trees encounter two contrasting environments. In cities, they reside within human-constructed spaces, often haphazardly planted with minimal foresight. In natural habitats, they combat challenges such as shifts in land use.
Ivonne Olalde Omaña, affiliated with the Institute of Biology at UNAM, underscores the crucial role trees play in sustaining life. “Without trees, without vegetation, life cannot flourish. Deforested soil not only erodes over time but jeopardizes our food sources and those of various wildlife,” she warns, emphasizing that a single centimeter of soil takes a millennium to form.
Every second Thursday of July, Mexico celebrates the Day of the Tree. This year, the spotlight is on July 13th. As Omaña, a biologist at the Iztacala School of Higher Education, points out, trees are indispensable for a range of ecosystem services, including moderating temperatures, retaining moisture, providing shade, emitting oxygen, acting as windbreaks, and halting soil erosion.
A recent report titled “State of the World's Trees” by Botanic Gardens Conservation International (BGCI, 2021) presents alarming statistics. Out of approximately 60,000 tree species globally, a third faces the looming threat of extinction, primarily due to altering land-use patterns. Specific to Mexico, while BGCI cites a figure of 3,620 tree species, the Instituto de Ecología A.C. believes the actual number could surpass 4,200.
However, it's not just about quantity. Olalde Omaña sheds light on the importance of planting indigenous trees. Local vegetation, having evolved over millions of years alongside the area's organisms, has intricate mutualistic relationships. Introducing foreign tree species disrupts these symbiotic relationships, leading to a loss in biodiversity and vital ecological interconnections.
“There's a complex web beneath the surface that we often overlook. The rhizosphere, replete with bacteria, fungi, and protozoa, has intricate connections with the native vegetation,” Omaña explains.
While citywide eradication of non-indigenous trees isn't practical or desirable, Omaña suggests a gradual shift towards native species, especially in newly designed public spaces. In Mexico City, for instance, while the vast ash trees, abundant in the Valley, might be suitable for parks, they're ill-fitted for sidewalks. A better fit? The native Tronadora (Tecoma stans), a close relative of the Jacaranda with vibrant yellow blooms.
Depending on the region, the tree choice needs adaptation. Eastern Mexico City, with its saline soils and water scarcity, could benefit from hardy species like acacias and mesquites. In contrast, areas like Magdalena Contreras, endowed with rivers and mountains, can support moisture-loving trees like “huele de noche” (Cestrum nocturnum), oaks, and willows.
Omaña concludes with a call to action for policymakers. “While every administration emphasizes reforestation, it's vital to understand that nature's cycles don't align with political tenures. We must view reforestation as a long-term investment in our future,” she asserts, pointing to the slow-growing oaks native to Mexico as a testament to this philosophy.
In essence, for a country rich in biodiversity like Mexico, safeguarding its trees isn't just an environmental duty but an ode to its cultural and ecological heritage.