Here's a problem to solve: Forest fires occur in many areas due to drought conditions. If the drought conditions continue for a long period of time, which might cause the repopulation of trees to be threatened?

Among the 4 following options, which is the correct answer?

- A: a decrease in the thickness of soil
 
- B: a decrease in the amount of erosion
 
- C: an increase in the bacterium population
 
- D: an increase in the production of oxygen
 