Surface energy dynamics and canopy structural properties in intact and disturbed forests in the Southern Amazon

Abstract

The Brazilian Amazon has been a focus of land development with large swaths of forests converted to agriculture. Forest degradation by selective logging and fires has accompanied the agricultural frontier and has resulted in significant impacts on Amazonian ecosystems. Changes in forest structure resulting from forest disturbances have large impacts on the surface energy balance, including on land surface temperature (LST) and evapotranspiration (ET). This study's objective is to assess the effects of forest disturbances on water fluxes and forest structure in a transitional forest site in the Southern Amazon. We used ET and LST products from MODIS and Landsat 8 and GEDI-derived forest structure data to address our research questions. We found that disturbances induced seasonal water stress, more pronounced in croplands/pastures than in forests (differences up to 20% in the dry season), and more pronounced in second-growth and recently burned areas than in logged and intact forests (differences up to 12% in the dry season). Moreover, ET and LST were negatively related, with more consistent relationships across disturbance classes in the dry season (R²: 0.41–0.87) than in the wet season (R²: 0.18–0.49). Forest and cropland or pasture classes showed contrasting relationships in the dry season. Finally, we found that forest structure exhibited stronger relationships with ET and LST in the most disturbed forests (R²: 0.01–0.43) than in the least disturbed forests (R² < 0.05). Our findings help to elucidate degraded forests functioning under a changing climate and to improve estimates of water and energy fluxes in Amazonian degraded forests.

Plain Language Summary: Deforestation, selective timber extraction, and forest fires are the main causes of forest disturbances in the Amazon region. These disturbances alter how forests function. Forest degraded by logging and fires may exchange less water and absorb less carbon dioxide from the atmosphere during photosynthesis. We used satellite-based observations on the amount of water transpired to the atmosphere by trees (known as evapotranspiration), land surface temperature, and forest structural properties such as canopy cover and height over a region in the Southern Amazon to understand the differences in function between disturbed and intact forests. We found that disturbances induced stronger and earlier water stress in the dry season in croplands and pastures than in forests, and stronger water stress in second growth and recently burned areas than in logged and intact forests. We also found that structural properties show a moderate relationship with evapotranspiration and temperature in the most disturbed forests, but weak relationships in the least disturbed forests. Our findings highlight the importance of intact forests in maintaining water balance in the Amazon region and suggest that disturbed forests may have limited ability to cope with the changing climate.

Citation

Rangel Pinagé, Ekena; Bell, David M.; Longo, Marcos; Silva, Carlos A.; Csillik, Ovidiu; Huete, Alfredo. 2023. Surface energy dynamics and canopy structural properties in intact and disturbed forests in the Southern Amazon. Journal of Geophysical Research: Biogeosciences. 128(9): 96-114. https://doi.org/10.1029/2023JG007465.