Here's a problem to solve: Some pine trees are able to live through forest fires because of their thick bark. After a forest fire, new pine trees can grow in the space left by other trees that burned down. How does thick bark help to increase the pine tree population?

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

- A: It produces more food for the tree.
 
- B: It increases the nutrients in the soil.
 
- C: It releases more oxygen from the tree.
 
- D: It decreases the competition for resources.
 