Brown MBL PhD student Xi Yang studies plant phenology or “the rhythm of the seasons”. Plant phenology is the timing of events such as leaf-out in the spring and senescence (color-change) in the fall, events which are sensitive to climate change. Phenology can serve as an important indicator of the impact of climate change on ecosystems. Changes in phenology also provide feedback to the climate system by, for example, changing the surface albedo. Xi uses remote sensing to monitor vegetation phenology at large spatial scales as well as models to predict future changes in phenology. He also uses a digital camera, spectroscopy and chemical analysis to understand the seasonality of plant physiology.
Remote sensing provides a tool for ecologists to understand large scale phenomena. Plant color changes throughout a season are easily captured by satellite sensors. Xi used a sensor named MODerate resolution Imaging Spectroradiometer (MODIS) onboard the satellite Terra and Aqua to monitor phenological changes in plants in New England. MODIS takes pictures at a time interval of half days, so Xi was able to create a time-lapse “photo” for his study area — New England, USA. From those images, he used a computer program to extract the time when the leaf turn green and yellow (or red).