True, but we're a long way from that, assuming the investment money is there. Look at situations like China and Brazil these days. Brazil's agro business is booming and expanding like crazy due to higher demand from China (a lot of business that American farmers used to get but I guess we're busy growing corn-for-ethanol instead nowadays). I have read that Brazil can still double its area under cultivation, and without clearing more rainforest. It just needs the investment money to do that, including building roads, railroads, ports, etc. to support all that additional capacity. (Actually, in fairness, most of that crop in Brazil bound for China is for animal feed because of their increasing ability to pay for meat, so the increased production there isn't really feeding more people.)

Who knows, one day we'll probably plow under Yosemite and Yellowstone if food prices got high enough. (Actually, I guess the pot growers are already ahead of the game in that department...)