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Remote light sensing technology has revealed that the fragmentation of the Amazon rainforest contributed one-third of deforestation carbon emissions in the region between 2001 and 2015.
 
Deforestation fragments forests, creating artificial edges and altering forest ecologies — known as ‘edge effects’. 
 
“Forest edges are more exposed to the sun, which dries vegetation out and raises local temperatures,” Celso Silva Junior, lead author of a study published in Science Advances (30 September), tells SciDev.Net.

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Co-author Luiz Aragão, a researcher from Brazil’s National Institute for Space Research, adds that higher local temperatures, less humidity and more wind can alter a forest’s climate.
 
Fishbone-like forest cuts create many edges, accelerating forest degradation. According to a new study, this geometry should be avoided in order to limit ‘edge effects’. This image shows the acceleration of deforestation around the BR-163 road in Pará from 2000 to 2019.
Credit: NASA Earth Observatory / Lauren Dauphin.

“Forests that were used to a specific climate become exposed to a different one and trees start to die. So, edge effects are quite strong in newly deforested areas, but they continue over time until the trees adapt to this new environment,” Aragão says.

How LiDAR works

LiDAR — Light Detection and Ranging — is used to measure distances and is most commonly found in satellites and aeroplanes, but is also used for laser guidance and self-driving cars.

Silva Junior’s international team of researchers used LiDAR to map biomass loss in new and older forest edges, and compared the findings with neighbouring, undisturbed regions to calculate carbon losses.

LiDAR is “as accurate as measurements made by researchers measuring trees on the ground. The difference is that it can cover more area in less time,” says Aragão.

“Forests that were used to a specific climate become exposed to a different one and trees start to die. Edge effects are quite strong in newly deforested areas.”

Luiz Aragão, Brazil’s National Institute for Space Research

The technology works like a large 3D scanner, emitting a ‘cloud’ of infrared lasers — similar to the way radar uses radio waves and sonar uses sound waves — Aragão explains.

The cloud of laser points sweeps the area, hitting tree canopies and the ground and measuring the distance between the two points.

The use of infrared light is an important feature of the technology. “The advantage of using infrared is that it captures heat to make images of vast areas,” says Victor Hugo Danelichen, a professor at the University of Cuiabá, Brazil, who did not take part in the study.

Credit: Vinícius Peripato (INPE)

“Not depending on sunlight for imaging allows for observations at night, too. Some plants make photosynthesis at night.”

The research provides a quantification of the carbon emissions of edge effects, something that scientists have long known about, says Flávia Costa, a researcher at Brazil’s National Institute of Amazonian Research, who did not participate in the study.

“This methodology should be included in impact reports,” she tells SciDev.Net. Costa adds that research at this scale conducted by satellites typically uses a coarser resolution and only considers deforestation, not edge effects.

 

Michael Keller, a researcher at the United States Forest Service, says measuring tree height with accuracy is important, because “forest height is intimately related to carbon stocks”.

Keller is one of the leaders of Sustainable Landscapes Brazil, a project that performs LiDAR surveys in the Amazon, Cerrado savannah and Atlantic Forest, and which provided LiDAR data for the study.

To Aragão, the study’s findings show that deforestation must be stopped.

“[W]here tree removal is needed, there must be more planning on the geometry of forest clearings to avoid edge effects as much as possible,” he says.

The study was supported by FAPESP, a SciDev.Net donor.

This piece was produced by SciDev.Net’s Latin America & Caribbean desk.