Seasonal Change and Phenology in Temperate Ecosystems

Phenology, from the Greek phainein ("to show" or "to appear"), is the scientific study of the timing of recurring biological events in relation to climate — bud burst, leaf-out, flowering, migration, and hibernation — and it exists as a formal discipline precisely because temperate and polar ecosystems are so strongly structured by seasonal change. Temperate deciduous ecosystems in particular display a tightly choreographed annual sequence: as day length and soil temperature increase in spring, deciduous trees break dormancy and leaf out, often preceded by a short-lived pulse of understory spring ephemeral wildflowers that exploit the brief window of high light reaching the forest floor before the closing canopy shades it; through summer, growth and reproduction proceed under maximal daylight; and in autumn, shortening day length and cooling temperatures trigger senescence, as trees actively resorb nutrients such as nitrogen and phosphorus from their leaves before abscission, the controlled shedding process that seals off and drops the leaf via a specialized layer of cells at the leaf's base.