Slowly Disappearing Canopy -
Tropical Forests in Peril

Tropical rainforests, often referred to as the "green lungs" of our planet, play a crucial role in maintaining ecological balance. These vibrant ecosystems are rich in biodiversity and essential for regulating the climate, sequestering carbon, and managing the water cycle.  Since 1990, 17 percent of these forests have  disappeared, releasing significant amounts of stored carbon back into the atmosphere and diminishing Earth's capacity to absorb the extreme carbon emissions anticipated in the future.

Protecting and restoring tropical forests is therefore a vital part of combating climate change. It is thus essential to refine our understanding and quantify human impacts on these forests with greater precision, with a particular focus on secondary damages that, though seemingly minor, accumulate and compromise the forest's capacity to support its ecosystem.

he protection and restoration of tropical forests are vital components in the battle against climate change. Tropical forest | Shutterstock, Panga Media

A View of the Forest from Space

In recent years, public awareness of deforestation and its environmental impact has grown significantly. While this heightened awareness has reduced extreme practices, such as large-scale forest clearing and burning, other activities—such as selective logging for agricultural expansion or infrastructure development within forests—have continued largely unchecked, as they are often perceived as less harmful to the environment. However, research shows that these smaller-scale actions accumulate over time, inflicting as much, if not more, damage to forests as large-scale deforestation.

In a recent study published in Nature, researchers analyzed data from NASA’s Global Ecosystem Dynamics Investigation (GEDI), a project utilizing a high-resolution laser aboard the International Space Station. The GEDI data enable the creation of detailed 3D maps of the intricate structure formed by treetops—the canopy—of tropical rainforests, along with the distribution of leaves and branches.  By integrating these insights with large amounts of satellite imagery spanning from the 1990s to the present, the researchers were able to quantify the extent of forest degradation, focusing on reductions in canopy height and tree biomass.

The researchers assessed the extent of forest damage by measuring canopy height loss and reductions in tree biomass. The image compres canopy height of undisturbed forests (top) with those affected by logging, fires, or other factors. In the second case the canopy height is significantly lower | From Bourgoin, C. et al., Nature 2024.

Slicing the Forest in Two

One often-overlooked human impact on forests is the "edge effect". At the forest's edge - whether near a road, agricultural zone, or areas cleared or burned during controlled operations - trees are exposed to increased environmental disturbances and face higher risks of harm. Infrastructure within the forest, such as roads or power lines, fragments the forest into smaller, disconnected patches, amplifying ecological disruption.

When people drive along a road cutting through a forest and see trees on both sides, they often believe they are still surrounded by continuous forest. This is a misconception. In reality, the road divides the forest into separate patches, weakening its ecosystem. Trees and plants near these boundaries become more vulnerable, and the natural communication between trees is disrupted. This disruption occurs because the fungal networks in tree roots—vital for transferring organic molecules that support growth and signaling—are severed. Fragmentation also increases wildlife vulnerability, exposing species to greater risks, including extinction, and contributes significantly to the reduction of forest biomass and resilience.

Researchers analyzing data from forest edges have demonstrated the severity of the edge effect: canopy height decreases by about 20% near the forest edge, with tree biomass similarly reduced. While earlier studies suggested that the edge effect extended only about 120 meters into the forest, new data reveal that its influence can reach over a kilometer deep.

Forest fragmentation leaves trees and other plants near the roadside more vulnerable. A road cutting through a tropical forest | Shutterstock, Zodar

The Domino Effect in the Forest

Beyond damaging the forest canopy and reducing biomass, researchers found that the edge effect accumulates over time, causing lasting impacts on the forest’s stability and its ability to recover from human disturbances and natural stressors, such as temperature fluctuations and wildfires. In some forests, canopy height and biomass levels failed to recover even 30 years after disruptions, such as road construction. The researchers estimate that full recovery could take hundreds of years. Alarmingly, plots where canopy height decreased by more than 50% showed no signs of recovery and continued to degrade, edging toward a state of near-total deforestation.

While the immediate and visible effects of deforestation and logging are well-recognized, this study sheds light on other, often overlooked, human impacts that receive far less public attention. Forest and land management policies need to account for the complexity and diversity of human influences on forest health, recognizing that a series of seemingly minor actions can collectively precipitate the collapse of an entire forest ecosystem. This awareness is crucial when planning construction within or near forests.

By adopting advanced technologies and comprehensive conservation strategies, we can work to preserve these valuable ecosystems for future generations.  The study's findings underscore the urgent need for sustained global efforts to safeguard the health of our planet's tropical forests.