Alder, "Alnus spp", is reported to be a good mulch with no alelopayhic properties noted that I have found. Most users report it will be digested in about a year. The one adverse comment indicated that if this is used as a mulch and piled up 6 feet it did suppress plant growth a lot.

lol, thanks. I imagine at 6 feet deep, most anything would hamper growth. But good to know the Alder doesn't have any of that *insert big word here* like the Black Walnut does.

Alder mulch has been my go to for clients. It was recommended by Earthfort in Corvalis to promote good soil biology, especiallly fungi. Chips work the best.