Abstract ID: 656

Shifts in Amazon seasonality and functioning with climate and disturbance

The functioning and fate of Amazon tropical forest ecosystems to climate change and land use pressures remain uncertain. Forest clearing and disturbance alter seasonal ecosystem functioning with potentially large consequences to water and carbon cycling, and combined with more intense or prolonged drought periods, Amazon forests may be stressed beyond their thresholds of resilience. Satellite studies have shown enhanced greening activity (related to photosynthesis) during dry, sunny periods in Amazon forests, attributed to the increased availability of sunlight. In contrast, cleared forest areas, with shallower rooting systems have restricted access to soil moisture supplies and are susceptible to drying during drought periods. In this study we analyzed and found wide variability in the seasonal-functional dynamics of intact, disturbed, and regenerating tropical forests of varying age classes, using fine and moderate resolution satellite data (EO-1 Hyperion and MODIS, respectively). The Hyperion data offer finer resolution and spectral detail but at infrequent time intervals, while the MODIS sensor provide high frequency but poor spatial/spectral resolution data. Our aim was to assess ecosystem seasonal-functional responses to variations in forest disturbance, regeneration, and climate. We found leaf flushing and green-up in regenerating forests during the dry season, dependent on age class, and similar to the light-driven seasonality of intact tropical forests. However, the regenerating forests exhibited a more complex seasonality due to the presence of two functionally different vegetation layers, a herbaceous understory and overstory tree layer, with opposite seasonal greening and browning physiologic activity. The drying effect was most pronounced in the younger and more open forest canopies, relative to the older, closed, and more developed regenerating forests. Knowledge of the behavior of multiple tropical forest layers would be needed to better characterize and model tropical forest seasonality and to better assess forest productivity, resilience, fire vulnerability, and water and carbon cycling.

Session:  Carbon - The role of seasonality in carbon and water balance.

Presentation Type:  Oral