What is so easy to forget is when things go wrong with a half-cut tree, or even with just a branch about to fall off it, major mayhem can result with serious consequences for the people involved, for fences, buildings and especially power lines. The latter can be very expensive indeed.
So there are some very basic things to do before you even start your saw. First decide which way the tree is leaning and which way it will fall. If there are heavier branches on one side this will certainly affect its direction of fall. The question is how tall is the tree to make sure there is enough space for it to fall into. Most people are get this wrong by a large margin which leads to very great surprises and often expensive damage of both their own and their neighbour's property.
The best way to ensure the direction of a tree's fall is to fix a rope to it and put this under tension while cutting. This is a very good idea but the first problem is to be able to get the rope high enough up a large tree to apply any decent leverage. You see some very dangerous attempts to do this from long ladders and from raised tractor buckets.
Most amateur tree fellers don't understand the physics of using wedges in the cut of a tree to start and move it, and how critical it is to cut leaving a hinge to hold the tree before it falls. This is why felling large trees should always be left to professionals.
One of the most dangerous situations is when the direction of fall is wrong and the tree gets "hung up" with other trees. Here the problem is that you never know when it's going to finish its journey to the ground – it could be minutes, days or weeks and somebody could get killed. Freeing such a tree is even more dangerous than it's initial felling.
The effects of wind on the direction of fall of a tree can be very unpredictable and even a light breeze can change a tree's direction at a critical moment, especially if the tree is in leaf. This can either jam the saw blade or slew the tree's line of fall. Removing a jammed saw if you haven't got another saw to cut and free it is very tricky operation.
Human nosey parkers are also a hazard when tree felling as the noise of a chainsaw always seems to draw them to see the action or maybe get some free wood. Once you have all your safety gear on with earmuffs and visor, and saw at full revs, it can be very alarming to find people have arrived to see what's going on and are standing in a high-risk area where the tree can kickback after falling.
The legal implications of trees going wrong can be horrendous, especially if property is damaged and power supplies damaged or cut. You will certainly get a large bill from the power company and your insurance company may not pay out. Your neighbour could be sending you a bill accompanied by a lawyer's letter for damages too.
Large trees should be only cut down by qualified arborists who are fully insured. The costs may appear to be high compared to your friendly neighbour's offer, but think about what can go wrong and who is going to pay if things don't work out the way they were intended.