Susan [it's Sarah, actually], you suggest that it is an assumption that producing our own means we make less demand on outside resources - correct?
But in that you are assuming that people who grow their own salad makings are then going out and buying - something - that replaces their former purchase of salad makings.
Certainly, natives should be included in our yards, but native plant gardens won’t reduce our depredation of wild land very much unless we also lessen our resource use. A native plant garden, while much easier on the environment than a lawn, does not change the fact that the owner is causing immense habitat loss elsewhere, out of sight [by consuming food and other resources produced in mass quantities]. But an ecological garden can change that. Every bit of food, every scrap of lumber, each medicinal herb or other human product that comes from someone’s yard means that one less chunk of land outside our hometown needs to be denuded of natives and developed for human use.