Trees on the Run: Out of Breath & Out of Time

This article is a precursor to the WFU Earth Talks series! A new, Ted-like event happening on Earth Day (April 22, 2021). To learn more about this topic, as well as several other sustainability themed subjects, register here! In person seats are full, so please select the livestream option on the page and access instructions will be sent to you via email. 

By Sophia Masciarelli (‘22)

When you hear the word “migration,” what comes to mind? Perhaps it sparks images of birds that fly south for the winter, or monarch butterflies making the journey across North America, or whales traversing the oceans of our planet. But what if I told you that trees are also capable of migration? 

While an individual tree is firmly rooted in the ground, as a species, trees can migrate over time. Such migration is in response to environmental challenges and climate change. Throughout the world’s forests, climatic shifts and other anthropogenic disturbances are disrupting the delicate natural balance of ecosystems, forcing plants and animals alike to relocate in search of more suitable conditions. This is especially pronounced in the Andean and Amazonian regions of South America.

These are some of the most biologically rich ecosystems on earth. According to John Kricher’s A Neotropical Companion, the Amazon Rainforest cycles more than 20 percent of the globe’s oxygen supply and functions as habitat for more than half of the world’s total species while only occupying 2 percent of total surface area. These landscapes also provide means of regulation for countless other global processes. Given their keystone importance, global biodiversity hotspots such as these serve as global priorities of conservation. Part of the equation for this biological treasure chest is the influence of elevation, temperature, precipitation, and other climatic determinants along a gradient in these regions. 

These and other key climate indicators result in distinct ecological zones with elevation diversity gradients of both plant and animal species. Each distinct biome is home to specialized organisms which are suited to thrive in their respective zones. These zones exist in a delicate balance. Anthropogenic disturbances including deforestation, increased greenhouse gas emissions, habitat fragmentation, and other global climatic changes have concrete and immediate effects on these areas. 

“The reasons for this are several,” says Dr. Miles Silman of WFU Biology for YaleEnvironment360. “Temperatures in the tropics are a lot less variable than at higher latitudes, so tropical species tend to have a narrow range of ‘thermal tolerance.’ Also in the tropics, temperature belts tend to be wider; thus, to track the temperature changes projected for the next century, tropical species will have to move a lot farther – and therefore faster – than temperate species. Meanwhile, because the tropics are already the hottest places on earth, temperature increases there will create ‘novel climates’ of a sort that probably haven’t been seen on earth in millions of years. Finally, and perhaps most significantly, the tropics are where most species actually live.” 

Dr. Silman has studied tropical ecology in Peru’s Manu National Park for more than two decades. By utilizing marked plots within a survey area, they can track the “movement” of tree species along these sensitive gradients. 

Despite this relatively short window of observation, the results are astounding. These trees really are moving. 

Species that were previously recorded in narrow bands are now popping up along higher elevations to maintain the environmental factors to which they are best suited. The ability to adapt is one key characteristic of life. These trees observed similar migrations during the last ice age thousands of years ago. However, the rate of change is millions of times quicker than anything the natural world has ever produced. This is a direct result of the encroachment and exploitative behavior of humans.

“The trees are moving up, but the treeline is not moving up,” Dr. Silman for Pulitzer Center.org. “And so there is this collision that’s happening. The more and more warming you get, the trees farther and farther down will get pushed up against this barrier, and they’ve got no place to go. So they will reduce their population sizes, and if this happens over large areas, it could drive some species extinct. And it could reduce the population sizes of many, many species.” 

In general, it is predicted that if tropical species continue to migrate at the rates observed here and are incapable of tolerating or adapting to rising temperatures, they will fail to keep pace with future climate changes, resulting in rapid losses of habitat area and high risks of extinction.

Observations and projections for mountain regions show a strong tendency towards upslope displacement of their biomes under future climate conditions. This is further exacerbated by habitat fragmentation caused by human development, which makes it even more difficult for trees to move once that barrier has been created.

The specific effects that these extinctions risk are not entirely understood in regard to global impacts. What is known, however, is that the ways in which ecosystems function, especially these ecosystems, are vast webs of interconnectedness in which organisms rely on each other for survival. The trees count on the birds and bats to distribute their seeds, birds count on trees and shrubs for habitat, flocks of birds become prey for larger animals to survive; everyone fits together like pieces of a puzzle, collectively making up the ecosystem. When one aspect is disrupted, it sends cascading effects all throughout the environment. The ripples are felt by all. 

Experts say that the combined impact of ongoing deforestation and escalating climate change on the Amazon Rainforest could radically transform its configuration by 2050. 

“Scientists say the potential loss of those species in the next 50 to 75 years could dramatically reshape life as we know it,” says Justin Catanoso, a WFU journalism professor and science journalist. “It’s not just about trees and plants dying off. Tropical forests are the functional lungs of the earth. They play a vital role in the water cycle and regulating weather around the world.”