Multiple-Time-Scale Dynamics of Tropical Forest Vegetation and Projections for Decision Support

Monday, December 9, 2019 - 13:40
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Temporal changes in TanDEM-X interferometric phase-height have suggested that phase-height dynamics at X-band are a good indicator of the rates of change of tropical-forest structure and aboveground biomass (AGB). Phase-height is a radar-power-averaged height, one of the principal observations of interferometric SAR (InSAR). Previous studies of InSAR phase-height for individual 50-m plots suggest that phase-height monitoring can detect deforestation within 1 month of the event, and can measure significant growth, given 3-year observing intervals. Here we suggest that TanDEM-X can measure significant growth on 1-2-year time scales. TanDEM-X InSAR data were taken at the Tapajós National Forest site in Brazil ~50 times, spanning 2011 to 2019. In addition to showing remote sensing images of the differences in phase-height between two epochs, we will show images of the rate of change of phase-height, estimated as a slope parameter from linear fits of 3-10 time points spanning 1-2-year intervals, over an 18 x 56 km contiguous area at Tapajós. Statistically significant trends are observed over these short time intervals, suggesting areal patches of different rates of growth. The correlation of those patches with stand structure and composition and local climate will be investigated to inform stakeholders as to biophysical correlates to spatial and temporal patterns of dynamics.

Multiple time scales (1 - 8 years) of InSAR structure and AGB change measurements over Tapajós are planned to train Landsat to monitor tropical forest AGB dynamics for CMS. The Landsat and TanDEM-X dynamics will be used to initialize an ecosystem demography model, Functionally Assembled Terrestrial Ecosystem Simulator (FATES) to predict system state 30 years into the future. For tropical-forest stake­holders, decision support depends both on monitoring AGB responses to decisions, and on modeling consequent future states based on different management and environmental scenarios. Planned meetings with stakeholders will be discussed.

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