Pine trees have adapted to winter weather and a shorter growing season with a conical tree shape that allows them to shed snow, and by staying green year-round so they can produce food through photosynthesis early in spring. Also, needle-shaped leaves reduce moisture loss.
The boreal forest or taiga of northern North American and Eurasia have mostly coniferous trees. Coniferous means bearing cones and is another word for pine trees. Much of this area was previously covered in glaciers and still has sub-surface permafrost. Winter may last up to six months, and summers last between 50 and 100 days. Trees in these regions adapted to survive climate conditions.
In winter the frozen ground prevents plants from taking water. Pine needles, with their small surface area, reduce water loss through transpiration. Pine needles have a waxy coating that protects them from drying winds and small amounts of sap that could otherwise freeze. Pine needles also contain a chemical that prevents animals from eating them. The dark color of the needles helps pine trees absorb heat from the sun, which again aids in photosynthesis early in spring.
Another reason pine trees are evergreen is because if they had deciduous-type leaves that fall off in autumn, they would have to expend much energy in their short growing season producing new leaves.