Why do pine trees retain their green color throughout the winter?

Pine trees are able to maintain green leaves, or pines, throughout the winter because of the nature of their leaves. Specifically, pine trees have needle-like leaves that prevent the escape of water through the stomata (slowing transpiration). This retention of water facilitates photosynthesis all year round as water is a necessary resource for conducting photosynthesis. Besides their shape, pine needles are covered with a waxy coating that retains water by slowing its evaporation. The combination of needle-shaped leaves and wax coatings allows pine trees—fittingly called evergreen trees—to persist in their green state throughout the year.