Here's a problem to solve: Mangrove trees are an important wetland inhabitant. Which is an example of a limiting factor in mangrove wetlands that is unrelated to the density of the mangrove wetland?

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

- A: amount of tannin in the bark
 
- B: severity of hurricanes per season
 
- C: number of days of sunlight per year
 
- D: size of stilt- like root systems per tree
 