Evergreen trees live in all kinds of climates; they differ from deciduous trees because evergreens maintain their leaves or needles all year long. They do not shed leaves during the fall, but instead adapt to the changing seasons without their branches becoming barren during the colder months.
Evergreens have the ability to absorb light and water and hold both in reserve to draw on when those vital resources are not available. Different types of evergreens adapt to the environment in which they grow and have a constant supply of energy that keeps them fully stocked with leaves all year long.
The design of the needles on an evergreen makes it possible for the trees to hold water better. They are much smaller than leaves on deciduous trees, and they have a wax-like coating that helps retain water. The size of the needles also allows evergreen branches to hold less snow in cold weather climates so the branches are less likely to get bent down and broken, even with the leaves surviving the fall and winter seasons.
The constant supply of needles or leaves on evergreens gives the appearance that the trees never shed their leaves, but that is not completely the case. Some leaves can last as long as 20 years, but some may replace their full supply in as short a time as a one-year period.