I would think that the choice of woods to be used
should follow the same principles as "what to plant". As an example, I think we all agree that a
polyculture of crops is superior to a monoculture crop. Likewise, using as many families of woods as are readily available, would have the same benefit.
A hugel bed made with nothing but pine would provide a single set of fungi, bacteria, and microbes. If the pines were not
native, they could drastically put the natural. native organisms at risk for survival.
A hugel bed with a dozen families of woods would introduce a much larger assortment of 'critters' to your soils.
If somebody were to offer me a free dump truck full of redwood bark, I would certainly not turn it down. But, I would have to make choices how I would utilize it. I might build one bed with it to exclusively grow plants that only thrive in a redwood forest. The remainder would be spread
thinly over a large area so as to not upset the balance of my native soils.