There are a number of websites that offer information on the best wood for heating. Generally, hardwoods such as Ash, Oak, and Hickory will be the very best. Softwoods such as pine and fir will have low heat values, burn up quickly, and produce a lot of creosote (but makes good kindling) There are a few toxic woods I would NOT burn, including poison oak, sumac, and treated lumber scrap. Treated lumber (may be called CCA, Tanalised, salt treated, or "green wood") is treated with heavy metals to keep bugs and fungus from destroying it.
Yes you can! Maple is one of the better fire woods to burn. Just make sure it's dry & not green wood.
Elm burns at medium heat levels, not as easy to burn and somewhat smoky. Not ideal as firewood. Not bad, if you have it, use it, but there are better woods if you are buying it.
While you can burn most woods, I would pass on the arborvitae. As an evergreen, you will get a LOT of creosote, fast burning, short lasting fires. It also contains a toxin believed to be a hallucinogen. A small amount used as kindling may not be a problem.
no
Yes it can
Check with Martin for an owner's manual. Unless a fireplace is specifically rated as multi-fuel, a gas fireplace cannot safely burn wood.
No, it is not safe to burn. It is toxic.
yes you can burn cactuse
You really should not burn ANY solid fuel in a gas fireplace.
I do.
Yes
Yes.