Firstly, read this.
From Afrigadget. The short and sweet of it is that some arid areas of Africa are susceptible to invasion by the Prickly Pear Cactus (aka nopales). Cattle stay away from it because of the spines, so it can grow and spread without any limits.
In an especially lean time, a farmer taught his cow to eat prickly pear as a last-ditch sustenance measure, after burning off the spines with another invasive plant. He and his cow now travel around, teaching other farmers and cattle how to use PPC as fodder, thus reducing the economic and environmental disruption that it causes, as well as providing free cattle food.
What do you know that you can teach your community? What do you want to learn? What is your prickly pear cactus, and where is your cow?