All terrestrial ecosystems are strongly influenced by water and its movement. Water cycles in and through ecosystems by rainfall and flow in streams and groundwater, and out of ecosystems through plant transpiration, evaporation, and flow through streams and groundwater.
Evaporation is the physical transformation of liquid water to water vapor.
In other words, the plant will conduct water from the soil to the atmosphere only if the atmosphere has a lower water potential than the soil. Furthermore, transpiration cools leaf surfaces because it absorbs heat energy. While transpiration is a key physiological process in plants, it is also a fundamental process characterizing terrestrial ecosystems through its contribution to evapotranspiration. In temperate deciduous forests, such as those of the northeast, transpiration is the major contributor to evapotranspiration during the growing season. Increased streamflow during autumn months is correlated with the slowing or stopping of transpiration at the end of the growing season.