Evergreen trees are trees which retain their foliage year-round, rather than losing their leaves annually like deciduous trees do. There are a number of different types of evergreens, and some distinct advantages to being evergreen as opposed to deciduous. Many tropical trees are evergreens, and evergreens are also very common in temperate climates. In colder regions of the world, evergreens are more rare, but still present.
From the tree's perspective, being evergreen requires less work. Deciduous trees require a lot of energy and nutrients in the spring, when they put out new leaves. Evergreen trees, on the other hand, conserve energy and nutrients by slowly growing new foliage year-round, which can be an advantage in regions where nutrients are tight, as an evergreen can endure a rough season, while a deciduous tree might fail. The leaves also provide insulation for the tree, preventing sun and frost damage on the branches and trunk. Evergreens also fertilize themselves, thanks to their nutrient-rich leaf litter, which also acts as mulch to protect the roots.
Some evergreen trees grow new foliage constantly, with older foliage dropping off as it is displaced. Others have slower rates of growth, losing leaves only periodically. In all cases, the foliage remains green and crisp year-round, with paler growth being newer. In spring, for example, new growth can appear almost yellow next to the more mature foliage. Most evergreens have needle-shaped leaves, to conserve water, and many evergreens have slightly waxy foliage, which also helps to prevent evaporation through the leaves.
Conifers such as cypress, pine, and fir trees are all evergreens, as are hollies, some oaks, eucalyptus, and rhododendrons, among others. As you can see from these diverse examples, evergreen trees come in an assortment of shapes and sizes. They can be found all over the world, from the harsh outback of Australia to the lush forests of South America.
Evergreen trees are popular as ornamentals because they retain their foliage year-round, rather than dropping their leaves in the fall and creating an unsightly mess. Deciduous trees can also create a very stark landscape in the winter when they lose their leaves. Evergreen trees keep the garden looking green and alive, even in snowy climates.
Many cultures also include evergreens in their folklore. These trees are associated with constancy, faithfulness, and other enduring traits, thanks to their persistent foliage. The practice of cutting evergreen boughs to use as decorations in the winter is also very common, especially in Northern climates, where the sight of green foliage is rare in the winter.