Christmas tree farm with fir, pine, and spruce.  As people head to the woods to pick out their perfect Christmas tree, check out this excerpt from  Woods Whys: An Exploration of Forests and Forestry  by Michael Snyder.        Ask any young child to draw a Christmas tree and chances are he'll draw something close to a triangle. If the kid is particularly tal­ented, she'll draw a cone. Indeed, the cone-shaped tree is as traditional as the holiday itself. Sure, there are the Charlie Browns among us who will settle for a less-than-perfect Christmas tree. But most of us look for a fir or spruce with just the right taper, symmetry, and conical form.      That conical shape is certainly the norm at most Christmas tree farms, and the short explanation for it is that the tree farmer shears them that way. Of course, there's more to it than that. Even if you are wandering afield in search of a wild Christmas tree far from any shears or knives,...