What exactly is a USA-NPN calibration species?
A USA-NPN plant calibration species is one of 20 plants selected to help “calibrate” phenological measurements across the USA. These native and introduced plants have broad distributions and are ecologically or economically important. The USA-NPN integrates observations on calibration species to get “the big picture” of plant responses. USA-NPN observers are encouraged to include at least one calibration species in their monitoring projects. Widespread observation of calibration species is needed so that the collective monitoring data for these plants can be integrated with climate measurements across the Nation. A committee of scientists developed the criteria for calibration species and selected the species. Their list of 20 had widespread review. The criteria for selection were 1) widespread distribution; 2) association with a dominant plant cover type; 3) relationships with other plants and animals; 4) simple identification of species with readily observable phenophases; 5) accessi
