Phenological events such as leaf emergence and senescence exert a direct control on both spatial and temporal patterns of carbon, water, nutrient, and energy cycling throughout all ecosystems. Phenology also regulates many aspects of vegetation feedbacks to the climate system through, for example, seasonal changes in albedo and surface energy balance. Recent work has shown that phenology is a robust indicator of the effects of climate change on natural systems, which convincingly demonstrates the need for improved monitoring of phenology at local-to-continental scales. We are developing a nation-wide network to monitor canopy phenology across a range of different ecosystem types. The objectives of this network are to provide unique insights into spatial and temporal patterns of phenological variation, provide a rich data stream important for validating satellite remote sensing phenology products, and offer the opportunity for scientists to link phenology to ecosystem function (e.g., exchanges of carbon and water). Three complementary tiers feature monitoring sites equipped with (1) networked, digital cameras (“webcams”) that make continuous observations of canopy state, (2) direct observations of phenological events (e.g., flowering, budburst) by human observers, and/or (3) calibrated radiometric instruments used to make measurements that can be linked to satellite observations or provide insights into the physical changes in canopy state tied to seasonality.
Results/Conclusions
Data products from all three tiers can be used to evaluate remote sensing phenology products and can also be combined with eddy covariance measurements (e.g., AmeriFlux network data) to evaluate relationships between observed canopy phenology and the phenology of ecosystem processes. International interest in these methods of phenological monitoring is also evident, with at least 26 webcams operating in conjunction with FLUXNET towers in South America, Europe, and Asia. Previous synthesis of webcam, radiometric, and eddy flux data indicate that leaf area development proceeded somewhat more rapidly than increases in canopy “greenness”. Springtime recovery of canopy photosynthetic capacity also tended to lag increases in canopy greenness. A nation-wide network will (1) contribute to international efforts to monitor phenology with simple imaging sensors, (2) promote improved understanding of community and ecosystem dynamics across biomes and ecosystem types, and (3) help reduce uncertainties in modeling of land surface processes in prognostic climate models.
