Maybe this will help explain how to but "spanners" ??
...of get me flamed/razzed LOL.
If the problem you are having is bucking a piece that spans a low spot or goes from a high bank down to a roadbed or trailtread here is one way to do it. Sounds more complicated than it is. Of course size everything up for side bends, widowmakers, landslides or limbslides from the uphill side of the road etc
Method is based on "felling" the log so that the upper end settles down onto the ground (or a log you have placed under the upper end).
But BEFORE you make that "felling" cut you set up your second cut by greatly reducing the diameter of the log where your second cut will be. You make two cuts and take a big wedge out of the bottom of the log. If the log is big enough or the lay is complicated you may have to narrow the log from side to side as well as cutting a wedge out of the bottom.
Then you do the sequence of cuts you would do if you were felling the tree. Take the face out of the top of the log. You are taking the face wide, and about 1/2 way through the diameter. Then undercut to trigger the drop. If the log is big enough cut the offside in about a third so when you do your undercut you are not reaching all the way under the log.
After the felling cuts you have a log or tree laying flat on the ground cut through completely where you made your felling cuts. Where you want to do the second cut is already almost through, and is easy to finish. After the second cut is done you have a piece cut through laying on the fireroad or trail flat on the ground that is only close to the pieces on either side in tow small lines cuz each side already has a wedge out of it.
SOUNDS MORE COMPLICATED THAN IT IS!
Here is a vid of a moderate Cedar I bucked this spring. Look at the span of the log across the trail tread at the end of the first video:
http://www.youtube.com/watch?v=veatGBgmbGk&feature=related
Then compare it to the end of the log at the right side of the frame in this video, let it start and then stop it right away for the best view:
http://www.youtube.com/watch?v=AEKld0g60FA&feature=related
You can see that the wedge was taken out of the right side of the frame, that is not the remnants of a salami cut.
You can see the log I had the guys stuff under the rootwad so it would not slide down into the trail before I did the "felling" cuts. I ususally can use the wedge from the "second"cut for that if need be.
Sorry I dont have vids of the cuts but I never think to get the guys to film me doing them. Dave.