Increased Occurrence of Large-Scale Windthrows Across the Amazon Basin

The Science

Windthrows, the uprooting or breaking of trees by winds, in the Amazon are produced by downdrafts associated with strong convective storms. Windthrows are a major natural disturbance that can influence forest structure, carbon balance, and species composition. A team of researchers documented an approximately fourfold increase in large (≥30 hectares) windthrows during the analyzed period from 1985 to 2020. Overall, researchers detected no changes in the size distribution or severity of windthrows over the past 35 years, except for an increase in very large events (>500 ha) since 1990. Thus, the number of events has increased.

The Impact

Given predictions of increased storm severity with global warming, the number of windthrows is also predicted to increase. This increase is likely to make wind disturbance an important mode of tree mortality, especially if large trees become more vulnerable to snapping and uprooting due to other emerging disturbances.

Summary

Convective storms with strong downdrafts create windthrows that locally alter forest structure, composition, and carbon balance. Using Landsat imagery from consecutive years, a team of researchers documented the temporal and spatial variation of large windthrows (≥30 ha) across the Amazon basin between 1985 and 2020. Over the 33-year period, the team identified 3,179 large windthrows. Windthrow density was highest in central and western Amazon regions, with about 33% of all events occurring within approximately 3% of the monitored area. In these “hotspot” regions, return intervals for large windthrows at the same location span centuries to millennia, while in the rest of the Amazon, return intervals exceed 10,000 years.

Data show a nearly fourfold increase in the number of windthrows and affected area, from 78 events (6,900 ha) in 1985 to 264 events (32,170 ha) in 2020, with an increase in events larger than 500 ha after 1990. These extremely large windthrows (ranging from >500 ha to 2,543 ha) drive interannual variation in median (84 ± 5.2 ha; ±95% CI) and mean (147 ± 13 ha) windthrow area. However, the team found no significant temporal trends in the size distribution of windthrows over time.

Principal Investigator

Robinson Negron-Juarez
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

Support was received from the Max Planck Institute of Biogeochemistry, German Academic Exchange Service (DAAD), ATTO Project funded by the German Federal Ministry of Education and Research (BMBF, contracts 01LB1001A and 01LK1602A), Brazilian Ministério da Ciência, Tecnologia e Inovação (MCTI/FINEP contract 01.11.01248.00), and Max Planck Society. Support was also received from the Balzan Foundation, Next-Generation Ecosystem Experiments Tropics, U.S. Department of Energy’s Regional and Global Model Analysis program area (Agreement Grant DE-AC02-05CH11231), and Reducing Uncertainties in Biogeochemical Interactions through Synthesis Computation (RUBISCO) Science Focus Area. Funding was also received from the Forest Data Connect of the National University of the Peruvian Amazon.

References