If you plant trees you should learn how to grow your own fungal inocculants to maximize your trees' health and growth. We published a story about it in The Permaculture Activist, issue # 61 (order a copy here).
The folks at the Rodale Institute also wrote about it and have posted the story online:
New Farm Research: Cultivating beneficial soil fungi to increase yields
Low-cost, on-farm system for producing mycorrhizal fungi inoculant takes another step forward.