He shows how man, in his attempt to settle areas of the prairie (its soil is rich and good for farming); selected areas near Oak stands, and while protecting their settlements from the prairie fires, inadvertently (or not) protected the Oaks. By doing so, the Oaks were allowed to grow larger and multiply, until " the grubs grew up into trees, and formed thickets so dense that it was difficult to walk through them, and every trace of the sunny Oak openings vanished.".
One of the most interesting parts of the book was the Odyssey chapter on "X" and "Y". Leopold wrote this chapter as an Atom (X) in the first person. He follows "X" throughout time and its journey as part of many different components of the environment. "X" finds itself as part of an Indian, a flower, a tree, a deer, the water, etc., eventually completing the natural cycle and winding up in the sea. The story of "X" takes place before western man had the opportunity to infringe on the environment, but this not the case for "Y". "Y" is an Atom who is confronted with the realities of a modernized world that has clashed with the natural order of things. When "Y" finds itself as an atom of soil, it is quickly washed away because of the thin loam. When it's a water atom, instead of calling a sparkling stream home, it becomes trapped in the oily sludge of a sewer. The two differing journeys were one of the best examples I have ever read on the impact of man on the natural world. The most thought provoking part of this chapter was the fact that Leopold puts everything under the microscope and gives the reader insight on how their actions can affect even the smallest of things in nature.
Probably the most important message that can be taken from the "Sand County Almanac" is that of the Land Ethic. Leopold tells of what ethics, in the human sense, relate to and then attempts to open the readers" eyes to expanding their concept of ethics to include the natural world around them.