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Phenology, the seasonal timing of biological events, plays an important role in the lives of people, plants, and animals. The emergence of leaves and butterflies and the seasonal migrations of birds are phenological events that signal a change in seasons.

Phenological events are some of the most sensitive biological responses to changes in climate. With a warming climate, shifts in timing are altering ecological relationships and processes. While the phenology of one species may change quickly, others may change slowly or not at all. For example, with extended, warmer summers, populations of mountain pine beetle can now complete their life cycle in one year instead of what previously took two years. The result has been an increase in outbreaks that are killing lodgepole, ponderosa, and whitebark pine in the Crown of the Continent.

Climate-driven changes can affect the phenology, abundance, and distribution of crops (as well as other plants) and their pollinators, which may alter the effectiveness of insect pollination. Observations of both insect and crop phenology is aiding in the understanding of the changes taking place.