I don't know the legal in's and out's for zoning and how a community can change zoning. I do know however, farm land in Bucks County was continuously rezoned to force out farmers and purchased by developers. Agricultural land in some communities was being taxed at the same rate as residential, and I know for a fact that the farmers had no say in the matter--even those who were proactive in local government.
The zoning of properties can typically be "upgraded" to a more intensive designation. This is because it would generally increase the value of the property. That's why its allowed, because the owner is not damaged, and in fact, the land is enhanced.
The downgrading of the zoning of a property is typically not allowed because it devalues the proeprty. In many case where government's wanted to downgrade zoning for environmental reasons, the owners have been compensated based upon the difference in value of their property before and after the zoning change.
Again, laws change from State to State and County to County. That's whay I say "generally".