Seminar: Jose David Urquiza Munoz

Natural disturbances have an important influence on the structure, composition, and functioning of tropical forests, and regulate biogeochemical cycles. Windthrows (i.e., snapped and uprooted trees by wind) are a recurrent and major natural disturbance in Amazon forests. However, we lack a more comprehensive assessment of how windthrows vary in frequency and severity across time in the Amazon basin. In this study we addressed the following questions: a) Are there regions with greater occurrence of windthrows in the Amazon, and how does the frequency of occurrence vary across these regions? b) What is the size distribution and severity of windthrows? and c) What is the interannual variation and respective area affected by windthrows? d) Are there detectable trends in their frequency over the last three decades?. To detect windthrows >30 hectares across the entire Amazon basin and assess their size distribution and variation across space and over time, we compared the fraction of non-photosynthetic vegetation in pairs of cloud-free images for time periods of five years, from 1985 to 2020. Our results show that windthrows are not randomly distributed as about 34% of them occurred in high dense regions that account for ~9% of the Amazon-basin area. We determined a mean event size of 252 hectares and a maximum of 1,877 hectares. Our conservative estimates indicate that 182,483 hectares (0.03% of Amazon basin) of forest were affected by windthrows in the eight studied years, ranging from 6,906 hectares (50 windthrows) in 1985 and 32,169 hectares (205 windthrows) in 2020. An apparent four fold increase in the number of windthrows from 1985 to 2020 could be related to observed increases in convective available potential energy (CAPE) over the same period. This is one of the first assessment of windthrow characteristics for the entire Amazon.

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