Science & Tech
Lower canopies indicate challenges for tropical forests
NASA technology assists researchers as they monitor the health of ‘Earth’s lungs’
Forests, due to their capacity to sequester carbon, are frequently referred to as the lungs of our planet; however, they are also susceptible to various global issues. A recent investigation, employing NASA laser technology from the International Space Station, uncovers the effects of climate change on worldwide tropical forests with unprecedented detail and scope.
This investigation, “Environmental drivers of spatial variation in tropical forest canopy height: Insights from NASA’s GEDI spaceborne LiDAR,” published in the Proceedings of the National Academy of Sciences, utilized data from the Global Ecosystem Dynamics Investigation (GEDI), a LiDAR laser system on the International Space Station, to examine alterations in tropical forest canopy height and assess how this vital metric has been influenced by heatwaves, droughts, and other factors related to climate change.
The forest canopy, which represents the highest layer of mature trees, “is an extremely vital indicator of forest vitality and ecosystem productivity,” described Shaoqing Liu, a postdoctoral researcher in Organismic and Evolutionary Biology (OEB) and the lead author of the study.
Shaoqing Liu.
Courtesy photo
“Generally speaking, taller canopies correlate with elevated carbon storage and increased above-ground biomass. Elevated canopies can mitigate the microclimate,” Liu noted, even aiding in lowering temperatures during heat events. The research examined tropical forests across Asia, Africa, and South America — territories with minimal interruptions or human activities like logging.
In order to evaluate alterations in these forests, his team utilized laser data from GEDI, enabling them to survey extensive forest areas globally, in contrast to earlier research which was confined to smaller regions.
“In recent years, NASA has leveraged the International Space Station as a practical platform for assessing innovative forms of space-based remote sensing measurements,” stated Paul Moorcroft, professor of OEB and the senior author of the research. “The Global Ecosystem Dynamics Investigation waveform LiDAR is a notable instance of this strategy.”
GEDI — pronounced “Jedi” — “provides insights into the vertical composition of the forest canopy,” including leaf density, according to Liu. “Our research illustrates that climate, terrain, and soil characteristics contribute to nearly three-quarters of the variability in tropical forest canopy height. Additionally, we identified that elevation, dry seasons, and solar radiation are the key factors influencing canopy height.”
The study revealed that “tropical forests in the southern Amazon region are particularly vulnerable to climate change” due to increasingly extended dry spells. “The dry season is the primary factor influencing forest canopy height in this region,” remarked Liu.
Given that global climate model forecasts indicate prolonged dry seasons in this area, “We may observe significant decreases in canopy height,” he further noted.
“Comprehending the environmental factors affecting tropical forest height is essential for evaluating the carbon sequestration and conservation importance of various tropical forest regions,” articulated Moorcroft. “Recognizing the environmental influencers of forest canopy height variation is also critical for predicting how tropical forests will engage with climate change.”
Nevertheless, the effects of climate change are not homogeneous. Utilizing GEDI, the researchers were able to identify variations in its expression and impact on the canopy. “In the central Amazon, due to its relatively damp conditions, the foremost significant factor is actually elevation,” explained Liu. The same pattern was observed in Africa, according to the findings of the researchers.
Looking towards the future, Liu aims to extend research beyond primary forests to investigate additional forest and woodland regions around the globe. He expressed hope that these investigations will influence environmental policy.
“Regarding climate-change strategies, we acknowledge that tropical forests are not only biodiversity hotspots; they are vital for carbon detention. Preserving them is crucial for climate change mitigation,” he emphasized. “We aspire to assist policymakers in identifying areas that are susceptible to climate change and prioritizing their protection.”
Funding for this research was partially provided by a NASA grant.