USA NPN National Phenology Network

Taking the Pulse of Our Planet

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Why Phenology?

Phenology is nature’s calendar—when cherry trees bloom, when a robin builds its nest and when leaves turn color in the fall. 

Phenology is a key component of life on earth.  Many birds time their nesting so that eggs hatch when insects are available to feed nestlings.  Likewise, insect emergence is often synchronized with leaf out in host plants. For people, earlier flowering means earlier allergies.  Farmers and gardeners need to know the schedule of plant and insect development to decide when to apply fertilizers and pesticides and when to plant to avoid frosts. Phenology influences the abundance and distribution of organisms, ecosystem services, food webs, and global cycles of water and carbon. In turn, phenology may be altered by changes in temperature and precipitation.  

Changes in phenological events like flowering and animal migration are among the most sensitive biological responses to climate change. Across the world, many spring events are occurring earlier—and fall events are happening later—than they did in the past. However, not all species are changing at the same rate or direction, leading to mismatches. How plants and animals respond can help us predict whether their populations will grow or shrink – making phenology a “leading indicator” of climate change impacts.

Critical applications of phenology include:

  • Management of invasive species and forest pests
  • Predictions of human health-related events, such as allergies and mosquito season
  • Optimization of when to plant, fertilize, and harvest crops
  • Understanding the timing of ecosystem processes, such as carbon cycling
  • Assessment of the vulnerability of species, populations, and ecological communities to ongoing climate change

The USA-NPN was established in part to assemble long-term phenology datasets for a broad array of species across the United States. Scientists use observational data in the National Phenology Database and models, such as the Spring Indices, to understand how responsive species and phenological phases are to changes in climate across time and space. This information can be used to determine the extent to which species, populations, and communities are vulnerable to ongoing and projected future changes in climate.  Explore our highlighted peer-reviewed publications to learn more about phenological research.