Also, it is much easier to roll a spruce needle between your fingers than the two-sided needles of other evergreens. As the ice sheets began to melt, the evergreen forest invaded the area and began their slow march north. The climate is still changing and trees are still migrating as the geographic range of every species changes continuously. Trees invade new territory when it becomes hospitable, and die out in areas when it becomes inhospitable. The conifers have an advantage over hardwoods in the north because the small needlelike leaves do not dry out as easily and because their evergreenness allows them to carry on photosynthesis whenever the weather is warm enough, even though those warm days are limited to a fairly short season here.
Conifers are also better adapted to inferior soils.
But because evergreen leaves last for several years its demands for nourishment are less than for deciduous trees which have to grow a whole new set of leaves every spring. Likely the most important adaptation of northern trees is their cold hardiness. Herbaceous plants that die back to ground level in winter are protected by the insulation of snow and whatever soil they grow in. In very hardy trees there are a great number of small, empty spaces where liquids inside the living cells can ooze into and freeze. Since the ice crystals do not freeze inside the living cells they will not do any damage to them.