It seems I first read in John Wiseman's, "SAS Survival Guide;"  ISBN 0 00 470 1674 (abridged, pocket sized), manual, that you could just chop down a tree, and start a fire in the center of it, in a survival situation  This avoids a lot of time and trimming.  As the fire burns, you can re-arrange the remnants of the tree toward the center.

I tried, this morning, burning such a fire using the dead wood from the wind storm, last week. A brush fire is much like what a survival fire may be like.  Burning the brush, in sections, from the tree that the wind storm twisted off, was used by me as an experimentation station for burning a survival fire.

You would not take a lot of time cutting and evening up the limbs of fallen trees, or whatever you could find, in a survival fire.  Same with my brush pile.

I had slabs, brush, and just an assortment of split logs from the tree.  The only parts I did not use for the experiment, was the split fire-sized logs, as you would probably not have them available in the wild, in an emergency.

The principle is that you just start a fire in the center, and let the branches "run wild," as it were.  As things burn down, you can "chunk" the partially burned branches into the fire, ( as they say in North Carolina.) 

Our ancestors may have made fire-lays as this.  There are other benefits, to such a fire-lay, I was not thinking about.  What happens is that the branches form a kind of natural heat barrier, or shield, and reflect much of the heat back towards anyone sitting near the fire.

To be sure, for cooking, one needs a more controlled space, and a bed of coals, as it were.  As this un-trimmed fire place burns, it does form some coals into a bed.  The matter is simple, from  here, to insert any burnable wood, down through the unburned branches on to the bed of coals.  The wood will promptly start burning. 

If the fire will only be needed for a short time, then it can be allowed to burn itself out, in the center, and it will leave a neatly formed ring of brush around it, such as will help in the next fireplace session.  If you need a  controlled sized bed of coals, start early with such a fire-lay.

There were some problems with such a primitively, and relative, uncontrolled fire lay.  At one point I wound up with a nice fire going under an over-laying bed of branches that were not burning, only kind of cooking, and drying out.  The solution, here, was to add some vertical members, pieces of wood, that would allow the fire to travel up and consume more of the branches.   Such a fire needs to be tended more than one made of neatly trimmed branches, formed in a ring.

To stir the fire you will need a fire stick.  Being in Commercial Construction, I have collected a three-quarter inch of electrical conduit, a hard pipe, about six feet long.  One end of the pipe is cut at a sharp angle, sort of like a hollow spear.  Makes a great fire stirring stick, walking stick that will "job" into moist ground when you stab down sharply, and I suppose a make-shift weapon in times of need.