Windthrow characteristics and their regional association with rainfall, soil, and surface elevation in the Amazon

Abstract

Windthrows (trees uprooted and broken by winds) are common across the Amazon. They range in size from single trees to large gaps that lead to changes in forest dynamics, composition, structure, and carbon balance. Yet, the current understanding of the spatial variability of windthrows is limited. By integrating remote sensing data and geospatial analysis, we present the first study to examine the occurrence, area, and direction of windthrows and the control that environmental variables exert on them across the whole Amazon. Windthrows are more frequent and larger in the northwestern Amazon (Peru and Colombia), with the central Amazon (Brazil) being another hot spot of windthrows. The predominant direction of windthrows is westward. Rainfall, surface elevation, and soil characteristics explain the variability (20-50%) of windthrows but their effects vary regionally. A better understanding of the spatial dynamics of windthrows will improve understanding of the functioning of Amazon forests.

Case Studies of Forest Windthrows and Mesoscale Convective Systems in Amazonia

“…It is worth noting that this linear relationship has large variance because the area of windthrows may be also driven by other factors such as forest resistance, wind direction, accumulated precipitation, etc. (Negron‐Juarez et al., 2023).…”

“…Increase in associated extreme precipitation with deep convections were observed in US under global warming , which could increase future tree mortality. It is worth noting that there is a significant spread in the linear relationship in Figure 1b, and regional variation caused by species and function traits (Aleixo et al, 2019), soil condition, and surface elevation (Negron-Juarez et al, 2023) can be important factors also affect the relationship.…”

Sensitivity of Optical Satellites to Estimate Windthrow Tree-Mortality in a Central Amazon Forest

“…We used the Purity Pixel Index spectral toolkit ([81], Figure S8) that relied on a wellestablished and reliable method that has been extensively used [1,14,16,17] to select the purest pixels from all images (e.g., areas where all trees were downed versus unaffected old-growth forest) to acquire the most accurate/representative endmembers of interest [27]. Finally, we conducted a SMA to compute fraction images of GV, NPV, and SHD [73].…”

“…These studies demonstrated that windthrows affect a large portion of the Amazon and occur with a range of intensities and sizes. The Central and Northwestern Amazon regions concentrate the highest incidence of large-scale (>30 ha) events [13,16,17].…”

“…Landsat offers broad coverage of the Earth's surface and long-term imagery data [18][19][20], allowing for reliable estimates of windthrow tree mortality at the stand, landscape, and regional scales [13,14,17]. However, robust estimates of tree mortality depend on the compatibility between the spatial resolution of optical sensors and the grain size of targets [21,22].…”