Impacts of Degradation on Water, Energy, and Carbon Cycling of the Amazon Tropical Forests

Selective logging, fragmentation, and understory fires directly degrade forest structure and composition. Their regional impacts on carbon, water, and energy cycles are com-parable to deforestation. However, studies addressing the effects of forest degradation on ecosystem functions are scarce. Here, we integrate field observations and high-resolution remote sensing from airborne lidar to provide realistic initial conditions to the Ecosystem Demography Model (ED2.2) and investigate the impact of disturbances from for-est degradation on gross primary production (GPP), evapotranspiration (ET), and sensible heat flux (H). We used forest demography information retrieved from airborne lidar samples (13,500 ha) and calibrated with 817 inventory plots (0.25 ha) across precipitation and degradation gradients in the Amazon as initial conditions to ED-2.2 model and simulated fluxes for five regions in Eastern Amazonia. Our results show that the magnitude and seasonality of fluxes were modulated by changes in forest structure caused by degradation. During the dry season and under typical conditions, severely degraded forests experienced water-stress with declines in ET (up to 34%) and GPP (up to 35%),and increases of H (up to 43%) and daily mean ground temperatures (up to 6.5°C) relative to intact forests. In contrast, the relative impact of forest degradation on energy,water, and carbon cycles markedly diminishes under extreme, multi-year droughts, as a consequence of severe stress experienced by intact forests. Our results highlight that the water and energy cycles in the Amazon are not only driven by climate and deforestation, but also the past disturbance and changes of forest structure from degradation, suggesting a much broader influence of human land use activities on the tropical ecosystems.