The PopClock is a citizen science project in which volunteers are helping University of Vermont and University of Maryland Center for Environmental Science scientists study how forest trees are responding to rapidly changing climatic conditions. PopClock volunteers are collecting ground-based observations of spring leaf emergence and fall color change of two poplar species—balsam poplar (Populus balsamifera) and quaking aspen (Populus tremuloides). They submit these observation to one of our partner organizations--National Phenology Network (NPN), Project Budburst, and Plant Watch. Scientists are using these observations to create maps of “green-up” and “green-down,” which they will combine with genetic information to identify areas where trees are most and least adapted to climate change. In fall 2015 and spring 2016, a small group of PopClock volunteers are also working with scientists to examine the use tiny remote sensors to measure forest phenology; this work includes an an all-expenses-paid trip to Vermont to learn about the sensors! PopClock is part of a larger research grant funded by National Science Fund. Please visit our website for more information; note our website includes a link for an application to join our special team of volunteer working with the remote sensors (due Sept 1 2015).