I am not a vegan, though I admire vegans' empathy. However, I have always questioned the plausibility of animal free
permaculture. Then, after having success with feeding my
chickens a large percentage of sprouted birdseed (cheaper than
chicken food and seems to be their preference and has improved laying), I came to a holy cow/no shit realization. Before I had
chickens I spread bird food where I wanted wild birds to
feed on insects as well as fertilize for subsequent garden plots. Now I use chickens/ducks/turkeys for fertilizer and food. It seems obvious now that one could simply optimize your system to encourage a ton of wild birds similar to running chickens and protect things strategically when starting them out or harvesting fruit. This also has run into my observation/theory about how vineyards and orchards that are left to the birds get fertilized as much as they feed the birds due to the nature of their one track digestive system that puts out what goes in at a pretty steady rate. My best friend has a vineyard in the willamette valley with several resident hawks that like this approach as well. I think the key for vegan farming is to still encourage animals, and by not harvesting them you could get their ecosystem benefits and produce vegetation very efficiently.