The PopClock is a partnership between Appalachian Lab (AL) and volunteers to study climate change impacts on poplar trees. With funding from the National Science Foundation, AL scientists are examining how forest trees are responding to rapidly changing climatic conditions. As part of this effort, we are working with US and Canadian volunteers, or “citizen scientists,” to collect ground-based observations of spring leaf emergence and fall color change of two poplar species—balsam poplar (Populus balsamifera) and quaking aspen (Populus tremuloides). We will use these observations to create maps of “green-up” and “green-down,” which we will combine with genetic information to identify areas where trees are most and least adapted to climate change. The results will be an important tool for forest management. We are partnering with the National Phenology Network (NPN), Project Budburst, and Plant Watch to recruit volunteers and manage the on-the-ground data.