The traditional downside of woodchips(especially fresh ones) is that the increased surface area allows them to decompose faster, and this causes them to rob the surrounding area of nitrogen for a while.
The key would be to use lots of manure/nitrogen sources to counter this; if you're doing this in a
hugel, that infill space that the woodchips will be taking
should otherwise have been full of these things anyhow.
As best I recall, while Alder is a nitrogen fixer, most of that would be in the
roots and leave rather than the woody part, but I could be mistaken.
A hugel of woodchips also wouldn't last nearly as long, as the woodchips, especially fast-rotting alder, will decompose much faster than logs... but it sounds like this would be in addition to larger
wood?
