What are monoculture tree plantations and monoculture plantations in general?

Monoculture means they grow only one species. As commonly used, it means one species is grown in such a way that it can be planted, tended and harvested by a machine in great quantity very easily. This is why modern agriculture is sometimes referred to as "a process of turning oil into food." Although this method gives us cheap food and other cheap products, it also consumes more energy than it produces. I read somewhere that it takes about 1.8 calories of oil to produce 1 calorie of food. Something to think about.