Determining phenological controls on ecosystem productivity among multiple biomes using digital cameras and eddy covariance data

Plant phenology drives the timing, magnitude, and variability in biosphere-atmosphere exchanges. Our understanding of phenological controls on carbon, water and energy fluxes remains limited. In this study, we use a network of digital cameras mounted on eddy covariance towers across multiple biomes (boreal and temperate forest, grasslands) to improve models of carbon and water exchange. We use a rich database of imagery for each of 14 sites to determine the timing and duration of seasonal “greenness”, evaluating its control on seasonal carbon uptake and rates of change in ecosystem productivity as well as daily carbon and water fluxes. For sites with multiple years of data, we evaluate the role of environmental variables (precipitation, temperature and radiation) in predicting interannual phenological variability, accounting for differential responses among coexisting species. This study forms the foundation for current efforts leveraging a global database of webcam imagery to monitor and model ecosystem response to climate change.