Key Characteristics
- Trigger: Severe convective storms, squall lines, and microbursts.
- Impact: Snaps and uproots canopy trees, causing up to 95% mortality in extreme events.
- Hotspots: 33% of detected events occur in just 3% of the Amazon basin.
- Detection: Sub-pixel Spectral Mixture Analysis (SMA) quantifying non-photosynthetic vegetation.
The Phenomenon & Meteorological Drivers
Windthrows are a major natural disturbance in the Amazon, generated by powerful downdrafts and downbursts associated with severe convective storms and large-scale squall lines. These intense localized wind gusts can reach speeds sufficient to snap and uproot massive canopy trees, creating forest gaps that range from a few individual trees to thousands of contiguous hectares.
Worryingly, the frequency of these events is escalating. Between 1985 and 2020, there has been a nearly fourfold increase in both the number of large windthrows (≥30 ha) and the total forest area they affect. This increase aligns with a long-term rise in extreme atmospheric instability (the top 95th percentile of afternoon Convective Available Potential Energy, or CAPE). The damage is highly concentrated; roughly 33% of all large events occur within specific "hotspot" regions in the central and western Amazon, which make up only ~3% of the basin's total area.
Carbon Cycle & Biomass Recovery
Intense windthrows instantly transfer enormous amounts of live aboveground biomass (AGB) into the dead wood pool (coarse woody debris), sometimes reducing local biomass by over 60%. As this necromass decomposes, it temporarily shifts affected patches of the forest from net carbon sinks to net carbon sources.
However, the capacity for biomass recovery varies drastically by region. In the highly productive Northwestern Amazon, forests exhibit remarkable resilience, recovering to >90% of old-growth biomass levels in approximately 20 years. This recovery rate is roughly 50% faster than that observed in the Central Amazon, suggesting that Northwestern forests may be evolutionarily adapted to more frequent and severe wind disturbances.
Forest Succession and Canopy Greening
The creation of large canopy gaps drastically increases light availability on the forest floor, triggering a vigorous, multi-decade successional response. By tracking the Enhanced Vegetation Index (EVI) over 32 years, we observe an initial sharp decline in greenness following the disturbance, followed by a rapid "greening" phase.
During the first decade of recovery, EVI steadily increases, often peaking at 20% above the levels of undisturbed old-growth forest. This elevated optical signature reflects the rapid colonization of fast-growing pioneer species, which possess highly reflective, broad leaves. As the forest matures over the next 15 to 30 years, longer-lived, late-successional species begin to dominate and form complex, multi-layered canopies, causing the EVI signal to gradually dampen and decline.
🌲 Interactive 3D Canopy Structure (LiDAR)
Loading 3D LiDAR Model...
Left-click and drag to rotate • Scroll to zoom • Right-click to pan
© Windthrow Inventory Database (WInD) - Urquiza-Muñoz et al., 2024 / MPI for Biogeochemistry
Modern Detection: The Wayra Approach
Traditionally, mapping these remote disturbances required extensive field campaigns. Today, observatories like WAOSUE leverage advanced techniques like Spectral Mixture Analysis (SMA) on optical satellite imagery. SMA decomposes the spectral signal of mixed pixels to estimate the proportional abundance of non-photosynthetic vegetation (NPV), green vegetation (GV), and shade.
The abrupt increase in the NPV fraction serves as a robust proxy for quantifying tree mortality and mapping the distinct "fan-shaped" geometries of severe windthrows. By integrating this physically based remote sensing approach with high-resolution 3D LiDAR and rigorous ground-truthed forest inventories, researchers can accurately bridge the gap between large-scale atmospheric phenomena and local forest ecology.
