Maybe it has to do with the concentration of ashes. Slash and burn practices might lay down a thinner layer of ash than RoseBlush1 did in her experiment:
>> I dumped a couple of cans of wood ash about nine years ago.
Or maybe, surrounded by tropical jungle, new duff accumulated faster than it does in her part of northern CA mountains.
I think it's a cool part of science, or generous on the part of nature, that most experiments raise more questions than they answer. It means we'll never run out of mysteries to explore.