USA NPN National Phenology Network

Taking the Pulse of Our Planet

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Early Results from the PopClock Project

Through the PopClock project, participants in Nature’s Notebook are collecting observations of spring leaf emergence and fall color change of two poplar species, balsam poplar (Populus balsamifera) and quaking aspen (Populus tremuloides). These observations are being compared to maps of “green-up” and “green-down.”

The map below shows locations where Nature’s Notebook participants submitted observations for either of the poplar species (grey dots). The observers’ reports of leaf-out and leaf color change at these locations will be compared to “greenness onset” as calculated from imagery collected by the The MODerate Resolution Imaging Spectrometer (MODIS) satellite. This estimate of the average day of year when green leaves are first detected each spring ranges from approximately day 60 (Mar 1) to day 160 (Jun 9) across North America.


Between January and August 2013, 12 observations of budbreak and expanding leaves have been collected on balsam poplar, and 534 have been collected on quaking aspen. The map below shows the geographic distributions of balsam poplar (in blue) and quaking aspen (in green) as well as locations that have submitted observations of poplar phenology so far.

These obsevations will be invaluable to researchers as they begin analyzing how genes and the environmental control poplar phenology, and how we can use satellite data to estimate poplar phenology over large areas.

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