Forest Degradation Impacts How Amazon Forests Photosynthesize

Researchers found that degraded forests (burned and logged) do less photosynthesis during the dry season but recover in about 4 years.

Forest degraded by fire (left) and selective logging (right) in southern Brazilian Amazon.

[Courtesy Rone Parente.]

The Science

Large areas of the Amazon Forest are being degraded through fires and logging. Using multiple remote sensing data, researchers tested whether degraded forests suffer more water stress than intact forests during the dry season. By comparing datasets of forest structure and photosynthesis, researchers evaluated how long it takes for forests to recover following disturbance.

The Impact

The study found that fires cause much more damage to forests than logging and that recently burned forests did less photosynthesis than intact forests. Burned and logged forests were already doing as much photosynthesis as intact forests only 4 years after a disturbance. However, the structure of burned forests remained very different from intact forests even after 14 years, suggesting that each forest characteristic may take a very different time to recover from degradation.

Summary

Humans cause disturbances, such as selective logging and fires, that degrade tropical forests, which alters forest structure and function. These changes also impact the ability of forests to uptake carbon. This study used airborne laser scanning data over the Amazon to investigate how forest structure varies across burned and logged forests of different ages since disturbance. The team also used solar-induced chlorophyll fluorescence (SIF) data from the TROPOspheric Monitoring Instrument (TROPOMI) mission. SIF is a proxy for photosynthesis, and the TROPOMI data provide information on how photosynthesis varies across seasons in degraded and intact forests.

The researchers found that forest fires suffered the largest changes in the vertical distribution of foliage and canopy height compared to logged and intact forests. Moreover, SIF in recently burned forests were significantly lower than in intact forests. In contrast, within 4 years after the disturbance, SIF values were higher in regenerating forests than in intact forests despite their lower leaf area. These findings highlight that degraded forests recover photosynthesis rates faster than they recover forest structure. The results also indicate that degraded forests can accumulate large amounts of carbon during recovery from disturbance.

Principal Investigator

Marcos Longo
Lawrence Berkeley National Laboratory
[email protected]

Co-Principal Investigator

Ekena Pinagé
Lawrence Berkeley National Laboratory
[email protected]

Program Manager

Brian Benscoter
U.S. Department of Energy, Biological and Environmental Research (SC-33)
Environmental System Science
[email protected]

Funding

This research was funded by the Australian Government Research Training Program Scholarship, the USDA Forest Service Pacific Northwest Research Station and International Programs, and the Next Generation Ecosystem Experiments-Tropics, funded by the Biological and Environmental Research (BER) Program within the U.S. Department of Energy’s (DOE) Office of Science. The research carried out at the Jet Propulsion Laboratory, California Institute of Technology, was under a contract with NASA.

References

Pinagé, E.R., et al. "Forest Structure and Solar-Induced Fluorescence Across Intact and Degraded Forests in the Amazon." Remote Sensing of Environment 274 112998  (2022). https://doi.org/10.1016/j.rse.2022.112998.