I have used a gas powered shredder, lawn mower with catcher bag, and a small yard vacuum to shred leaves. Surprisingly, the yard vac does a very nice job of mulching wet or dry leaves into fine shreds. I can start it myself even though it's a pull starter. Comment on alders and nitrogen: Alder roots have abundant nitrogen-fixing bacteria, but the leaves are not extraordinarily high in N, so there should not be problems with promoting the wrong fungi from composts with alder leaves. I have found that alder wood chips inoculate quickly with mycelia when piled on the ground, and even faster if layered with cardboard. This inoculated material is a great mulch in the garden among perennials and shrubs. Kathleen