One thing I would expect from a hot fire, besides burning off all organic matter is sterilizing the ash, dust, sand and grit left behind. But rain and wind correct that quickly!
>> something different in wood ash vs. volcanic ash
Excellent point! They shouldn't be the same word. Wood ash is metal oxides that turn into hydroxides with water: concentrated caustic. Calcium hydroxide, magnesium hydroxide, sodium hydroxide and a little iron hydroxide, I think.
Volcanic ash is powdered rock, a.k.a rock dust. MUCH more benign as a starting point for pedogenesis!
>> I dumped a couple of cans of wood ash about nine years ago. Nothing has growth there since
I would have expected the caustic to leach out eventually. But maybe the metals left behind are so concentrated that they're toxic.
You might experiment by acidifying that dead soil, perhaps checking the pH first. "Agricultural sulfur" or finely powdered sulfur is oxidized by certain bacteria, in effect releasing a larger weight of sulfuric acid than the original sulfur weighed (all the added oxygen what it became sulfate, SO4).
That would neutralize the remaining wood ash, although it would still leave the metals behind as metal sulfates instead of metal hydroxides.