Here is a great article on plant associations and communities. The same idea as companion planting but on a Permaculture scale :-) http://www.vegetariat.com/2015/11/plant-guilds-work-1/
[Quote] The Southern California hills and mountains there are small forests of tall shrubs called California lilac, or ceanothus. Ceanothus is a nitrogen fixer (I’ll go into what that is in another post), so it is building soil as it grows and dies. I met a man who is receiving government funds to ‘reforest’ a portion of local mountains, and he’s bulldozing acres of ceanothus and planting pine trees in their stead. The soil isn’t ready for pine trees, which is the soft wood stage of succession. As we are going into decades long drought, and there is great tree loss due to a pine beetle, his project is doing much more harm than good. In fact, he has such a small success rate that I wonder why he’s still pursuing the project.
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I know someone just like that. Spraying Roundup all over the hills around Julian to kill the California lilac (ceanothus) in order to plant pine trees –in a fire zone.
He is always interested in helping by telling me what I’m doing wrong when I am digging up my waterline or working out in the yard. He is such a wonderful neighbor.