Concept:Overgrazing damages pasture land and reduces the quality of grazing resources.
The question asks which option is NOT an effect of overgrazing.
Explanation:Overgrazing leads to the removal or depletion of useful fodder crops, so option A is a real effect.
It also exposes the soil, causing soil erosion and wind erosion on pasture land, so option B is a real effect.
Heavy grazing reduces the availability of good pasture and creates scarcity, so option D is a real effect.
An epidemic of cattle diseases is not a direct result of overgrazing.
Disease outbreaks may occur, but they are not considered a primary geographical or ecological effect of overgrazing.
Therefore, option C is the exception.
Answer:C. epidemic of cattle diseases.