Trees that lose their leaves in winter are known as deciduous. The technical term for this process is leaf abscission. Leaf abscission is a defense mechanism: in colder climates, the water contained in the broad leaves of deciduous trees could easily freeze and expand, destroying the leaf cells. It is unlikely the leaves would survive. By dropping their leaves, trees protect themselves from frost damage and conserve energy in the winter months. During this dormant phase, the tree does not spend energy on growing new leaves. The leaves of deciduous trees normally have a green colour due to the presence of the chlorophyll pigment they contain, which is used to carry out photosynthesis. During the leaf-abscission process, chlorophyll is reduced, and, in some trees, orange and yellow pigments become visible as the green disappears. Evergreen plants don't need to drop their leaves because they are covered in wax and resins which stop them from freezing.