I forgot to answer that question yesterday but, yes, I can tell the species of most trees by looking at them. It's easy when the leaves are on them but, in the winter, you have to tell from the bark and the general shape of the tree. It also helps if you identified the tree last summer and remember which one it is. This one is a sugar maple, or maybe it's a red maple, the books are not all in agreement about that. Suffice it to say it's a maple. This one is an old maple, past its prime. The younger ones have smooth grey bark and, of course, are smaller. I decided to cut this one because of the way the two trunks were growing together. If allowed to continue growing that way, they would eventually merge into one trunk, but might split apart unexpectedly when I or somebody else was felling the tree in the future, which would be dangerous. As it was, I made a vertical cut between the two trunks to make sure they would separate cleanly so I could fell them one at a time in the direction they were leaning.
Nobody uses an axe anymore to fell a tree, we all use chain saws nowadays. First you make the undercut, or notch cut. This is the part they used to do with axes. First they would make a horizontal cut with a hand saw, then they would chip away with the axe to widen it out into a notch. It's much easier to do the whole thing with a chain saw, and one person can do it by himself. It took two people to operate those long cross cut saws they used to use. You make the undercut on the side of the trunk that you want the tree to fall towards. Most trees have a certain amount of lean to them, and it's best to go with that. An experienced logger can sometimes make a tree fall on an angle from the lean, but it's a tricky business that I try to avoid whenever possible. If you miscalculate the lean or, if a gust of wind blows against the lean at a critical moment, then tree can go back on you. More about that later.
After you have completed the undercut, you make the back cut, which is a horizontal cut on the opposite side of the trunk from the undercut, and a little higher than the flat part of the undercut. If I hadn't had the other trunk to deal with, I could have just made the back cut straight on. In this case, I had to use a plunge cut, but that's kind of technical, so we won't go into that right now. You should not have to make the back cut all the way through to the undercut. When the tree starts to tilt, you want to pull your saw out of the cut and back away from the tree. If the tree starts to go back on you, it might pinch the saw in the back cut. If that happens, abandon the saw and get away from the tree because you don't know what it's going to do next. If I go into all the possible scenarios, we'll be here all night. Suffice it to say that, if the tree falls in the intended direction, the last little bit that you didn't cut will break cleanly at a point called "the hinge". This is what you want it to do because it keeps the tree falling straight instead of letting it turn to one side or the other. As it is, the tree is likely to bounce or roll when it hits the ground. You can see in the second picture that this tree did not end up laying right straight out from the stump. That's why you back away when the tree begins to tilt. Back away, don't run away! You want to keep your eye on the tree as it goes down. If it does something strange, just step out of the way.
You may be right about the concept of straight lines originating with the surveying of property lines between farm fields. Sometimes there was a natural division, like a creek or ridge line, and they would go with that. When it was necessary to create an arbitrary boundary, a straight line would have been the easiest thing to work with. There's also the thing about weapons, like spears and arrows. Trial and error would have taught them that a straight shaft flies truer than a crooked shaft. When it comes to structures, though, a square or rectangle is not the easiest thing to make out of natural materials but, if you're using sawn or hewn timber, it certainly is. I wonder how long it took them to figure that out.
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