Most folks know I live very remote. Now that that's out of the way I don't have a great amount of choices. I have my own Willow trees planted, those are called Navajo Willow and they grow well here.
I've also read/heard about grape vines, not so many of those here. Around here a native tree grows called a Utah Juniper which is a very hard wood. But from what I understand the best is the willow.
Now does it make a difference as to what specific type of willow is used to make the coal from?
I did a search on the net and when you search Willow there seems to be an awful lot of types.
Edit.....ALSO.....does it make a difference how big the branches are. Does a person want to use the smaller 1" or less or is it a simple case of size doesn't matter.