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Windthrows can influence the structure, carbon balance and species composition of the ecosystem. A new study, led by the Max Planck Institute for Biogeochemistry, Germany, now mapped and calculated windthrow events over the entire Amazon basin from 1985 to 2020. The researchers found that about one third of all events occurred in only three percent of the monitored area. They also found that the number of large windthrows and the total area of impacted forests increased about fourfold in the period analyzed. This increase can be associated with changes in atmospheric conditions.
Strong storms can cause downdrafts that damage forests by breaking or completely uprooting trees. Such windthrow events are an important natural disturbance in forests worldwide. They may range in size from few square meters to several hundred hectares, and affect the forest’s structure and composition. Since climate change increased the number and intensity of powerful storms, windthrows may have increased as well.
David Urquiza-Muñoz, PhD student at MPI for Biogeochemistry in Jena, Germany, addressed this question in the Amazon rainforest by developing an annual database of large windthrows that occurred between 1985 and 2020. Urquiza-Muñoz and his international colleagues used data from Landsat satellites, comparing images from one year to the next and searching for windthrown areas with specific geometric features and where toppled trees altered the spectra of reflected light. This method allowed researchers to identify large-scale windthrows covering more than 30 hectares.
“We found a nearly 4-fold increase in the number of large-scale windthrows and their associated area from 1985 to 2020” says Urquiza-Muñoz, first author of the recently published study. This finding supports observations that intense storms in the Amazon, a region with rather few continuous long-term climate records, are becoming more common.
On a local level, large-scale windthrows are thought to be rare events. However, Urquiza-Muñoz and colleagues also found that roughly a third of all windthrows occurred in only about 3 percent of the vast Amazon basin. “Surprisingly, some areas seem to have a higher windthrow activity than others” Urquiza-Muñoz says. For example, large windthrow events were more common in the central and western Amazon.
Large-scale windthrows can trigger ecological succession, thus influencing forest structure and composition for the following decades to centuries. “This indicates that wind disturbance is likely shaping landscape structure and composition in regions where they occur most” says Susan Trumbore, Director at Max Planck Institute for Biogeochemistry and coauthor of the study.
The ecology and functioning of old-growth Amazon forests did not change drastically over the past 35 years. Also, the size and severity distribution of individual windthrows has not consistently changed over time. The researchers therefore postulate that the overall increase in large-scale windthrow events is primarily caused by changes in atmospheric conditions, i.e. the frequency of damaging winds has increased.
There were large variations in windthrow events between different years that cannot be explained by common causes of Amazon climate variability such as El Niño and La Niña. However, the new publicly accessible database provided by the group will prove useful for future studies on the specific meteorological conditions leading to windthrows and ultimately their impacts on forest dynamics and diversity. In addition, improved satellite imagery resolution and application of LiDAR technology could further improve detection and understanding of windthrow effects in future.
The windthrow study was recently published in AGU Advances and highlighted in the science news magazine Eos. The work represents a multi-year collaboration of the Max Planck Institute for Biogeochemistry and the Geography Department of the Friedrich Schiller University, both in Jena, Germany, the Faculty of Forestry Science from the National University of the Peruvian Amazon in Peru, the Lawrence Berkeley Laboratory in California, USA, and the Julius Kuehn Institute for Forest Protection in Braunschweig, Germany.
Prof. Susan Trumbore, Ph.D.
Director, Department Biogeochemical Processes
Max Planck Institute for Biogeochemistry
phone +49 3641 57-6110
email trumbore@bgc-jena.mpg.de
Jose David Urquiza-Munoz, MSc.
Max Planck Institute for Biogeochemistry
email jurquiza@bgc-jena.mpg.de
Dr. Daniel Magnabosco Marra
Max Planck Institute for Biogeochemistry
Julius-Kühn-Institut für Waldschutz, Germany
email dmarra@bgc-jena.mpg.de
J. David Urquiza-Muñoz, Susan Trumbore, Robinson I. Negrón-Juárez, Yanlei Feng, Alexander Brenning, C. Michael Vasquez-Parana, Daniel Magnabosco Marra
Increased Occurrence of Large-Scale Windthrows Across the Amazon Basin
AGU Advances,5, e2023AV001030.
https://agupubs.onlinelibrary.wiley.com/doi/10.1029/2023AV001030
https://agupubs.onlinelibrary.wiley.com/doi/10.1029/2023AV001030 original publication
https://eos.org/research-spotlights/storms-are-knocking-down-more-and-more-trees... Eos spotlight
https://www.bgc-jena.mpg.de/bgp Department Trumbore
Windthrow in the Amazon
© ATTO/MPI-BGC
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