COS 38-4 - Surface energy dynamics and canopy structural properties in intact and disturbed forests in the Southern Amazon

Abstract: The Southern Brazilian Amazon has been a focus of land development with large swaths of tropical forests converted to agriculture. The degradation of forests by selective logging and fires has accompanied the advance of the frontier and has resulted in significant impacts on Amazonian ecosystems. Changes in forest cover and structure resulting from forest disturbances have large impacts on variables influencing the surface energy balance, including land surface temperature (LST) and evapotranspiration (ET). The objective of this study is to assess the effects of forest disturbances on the seasonal water fluxes and canopy structural properties (e.g. plant area index, canopy cover, canopy height, and foliage height diversity) in a transitional forest site located in Mato Grosso State, Southern Amazon. We use ET and LST products from MODIS and Landsat 8 as well as GEDI-derived forest structure data to address the following questions: a) What is the effect of forest disturbances on the seasonal water stress of the canopy? b) How are variations in seasonal water stress manifested in LST-ET relationships across the study site and do these relationships vary with season and disturbance severity levels? c) What is the contribution of canopy structural properties to ET and LST and how does time since disturbance alter the strength of their relationship? We found that disturbances induced increased seasonal water stress, more pronounced and earlier in croplands and pastures than in forests, and more pronounced in second-growth and recently burned areas than in logged and intact forests. Moreover, we found negative ET and LST relationships, more consistent across disturbance classes in the dry season than the wet season, and that forest and cropland, and pasture classes showed contrasting relationships in the dry season. Finally, we found that canopy structural properties exhibited moderate relationships with ET and LST in the most disturbed forests, but negligible correlations in the least disturbed forests. Our findings are relevant for understanding the degraded forests functioning under a changing climate, and improving estimates of seasonal water and energy fluxes at heterogeneous forests such as those in the Southern Amazon.