The Science

Windthrows (gaps of uprooted or broken trees) are a recurrent disturbance in Amazonia that affects the persistence of woody biomass, which, in turn, affects patterns of productivity and biomass, floristic composition, and soil composition in the basin. Windthrows are produced by severe convective events that are expected to be more frequent with climate change. Yet, the variability of windthrows over time has not been investigated. Studying the frequency of windthrow occurrence is key to understanding the atmospheric conditions that produce these events.

The Impact

Project results show that windthrows occur every year and were more frequent from September through February. Drivers of windthrows include southerly squall lines (that form in southern Amazonia and move to northeast Amazonia) that were found to be more frequent than their previously reported ~50 year interval. Project results will improve representations of tree mortality in ESMs and, in particular, the ACME Land Model (ALM).

Summary

Windthrows are a recurrent disturbance in Amazonia and are an important driver of forest dynamics and carbon storage. In this study, researchers present, for the first time, the seasonal and interannual variability of windthrows, focusing on central Amazonia, and discuss the potential meteorological factors associated with this variability. Landsat images from 1998 through 2010 were used to detect the occurrence of windthrows, which were identified based on their spectral characteristics and shape. They were found to occur every year, but were more frequent between September and February. Organized convective activity associated with multicell storms embedded in mesoscale convective systems—such as northerly squall lines (that move from northeast to southwest), and southerly squall lines (that move from southwest to northeast)—can cause windthrows. The researchers also found that southerly squall lines occurred more frequently than their previously reported ~50-year interval. At the interannual scale, the study did not find an association between El Niño–Southern Oscillation and windthrows.

Principal Investigator

William Riley
Lawrence Berkeley National Laboratory
wjriley@lbl.gov

Program Manager

Daniel Stover
U.S. Department of Energy, Biological and Environmental Research (SC-33)
Environmental System Science
daniel.stover@science.doe.gov

Funding

This research was supported as part of the Next-Generation Ecosystem Experiments (NGEE)–Tropics project and the Regional and Global Climate Modeling program, both funded by the Office of Biological and Environmental Research, within the U.S. Department of Energy Office of Science, under Contract No. DE-AC02-05CH11231.

References