All pine trees have needles, but all needled evergreens aren't pine trees any more than all dogs are dachshunds. Telling pines from firs from spruces isn't any harder than distinguishing beagles from Bassett hounds from bloodhounds -- you just need to know how each one is distinctively different from the others.
A distinguishing trait of pine trees is that their leaves (the needles) are bundled together, usually in packs of two to five. The needles may be long or short or somewhere in between, but if you find needles in bundles, you have a pine tree.
If you examine a needle from a tree and find out that it's not round and not flat but rather four-sided, you are looking at a spruce needle. The color may range from dark green to quite blue, but if the needle rolls between your fingers as smoothly as a square wheel, it's a spruce.
If you try this with a fir needle, it won't roll at all because it's flat. Like spruce needles, fir needles don't grow in bundles, either. Like spruce trees, fir trees tend to be tall, dark and symmetrical. Like pine trees, some types of fir trees are used for Christmas trees. Spruces, however, tend to lose their needles too quickly once they're taken indoors, though their shape makes them good candidates for outdoor lights around the holidays.
I think it has to do with the amount of pitch in the different woods..
