Using time series of MODIS land surface phenology to model temperature and photoperiod controls on spring greenup in North American deciduous forests

The timing of leaf emergence in temperate and boreal forests is changing, which has profound implications for a wide array ecosystem processes services. Spring phenology models, have been widely used to predict the emergence, generally assume that combination photoperiod thermal forcing control when leaves emerge. However, exact nature magnitude how temperature individually jointly subject ongoing debate. Here we use continuous development model with time series land surface measurements from MODIS quantify relative importance controlling canopy greenup eastern North America. accurately predicts biogeographic interannual variation across study region (median RMSE = 4.6 days, median bias 0.30 days). Results reveal strong period prior influence covaries versus controls. Photoperiod on dominant warmer climates, but exerts only modest colder climates. models estimated using ground-based observations cloned lilac are consistent those remote sensing, supports realism sensing-based models. Overall, results this suggest apparent changes sensitivity trees reflect trade-off between decreased increased control, identify transition near 10 °C isotherm mean annual temperature. This suggests will continue move earlier as climate warms, change be more pronounced regions temperatures below °C.