Why Pine Trees Are Evergreen

Almost all the trees turn into yellow in winter,but the pine trees are also green,they are evergreen,why?let me introduce the details to you.
Pine tree is evergreen is because its leaves have evolved into pine needles, so the water is evaporated is very few, keep chlorophyll is more also. And pine trees are not leaves, it is in constant change the leaves, just a falling leaf is not so much, time leaves in the four seasons of different time, not carefully observe, really thought is evergreen!

The pine needles longer life expectancy, general is 1 year to 5 years, and not regularly falling leaves.
Pines are native to most of the Northern Hemisphere. In Eurasia, they range from the Canary Islands, Iberian Peninsula and Scotland east to the Russian Far East, and in the Philippines, north to just over 70°N in Norway, Finland and Sweden (Scots Pine) and eastern Siberia (Siberian Dwarf Pine), and south to northernmost Africa, the Himalaya and Southeast Asia, with one species (Sumatran Pine) just crossing the Equator in Sumatra to 2°S. In North America, they range from 66°N in Canada (Jack Pine and Red Pine), south to 12°N in Nicaragua (Caribbean Pine). Pines have been introduced in subtropical and temperate portions of the Southern Hemisphere, including Chile, Brazil, South Africa, Tanzania, Australia, Argentina and New Zealand, where they are grown widely as a source of timber. A number of these introduced species have become invasive, threatening native ecosystems.
Pines are evergreen, resinous trees (or rarely shrubs) growing 3–80 m tall, with the majority of species reaching 15–45 m tall. The smallest are Siberian Dwarf Pine and Potosi Pinyon, and the tallest is a 268.35-foot (81.79-meter) tall Ponderosa Pine located in southern Oregon's Rogue River-Siskiyou National Forest.
The bark of most pines is thick and scaly, but some species have thin, flaking bark. The branches are produced in regular "pseudo whorls", actually a very tight spiral but appearing like a ring of branches arising from the same point. Many pines are uninodal, producing just one such whorl of branches each year, from buds at the tip of the year's new shoot, but others are multinodal, producing two or more whorls of branches per year. The spiral growth of branches, needles, and cone scales are arranged in Fibonacci number ratios. The new spring shoots are sometimes called "candles"; they are covered in brown or whitish bud scales and point upward at first, then later turn green and spread outward. These "candles" offer foresters a means to evaluate fertility of the soil and vigour of the trees.

Pines are long-lived, typically reaching ages of 100–1,000 years, some even more. The longest-lived is the Great Basin Bristlecone Pine, Pinus longaeva, one individual of which, at around 4,600 years old, is one of the world's oldest living organisms. This tree can be found in the White Mountains of California. An older tree, unfortunately now cut down, was dated at 4,900 years old. It was discovered in a grove beneath Wheeler Peak and it is now known as Prometheus after the Greek immortal.