Step 1: Understand the dynamics of savanna ecosystems.
Savannas are grasslands with sparse trees. Several factors influence tree density in these
ecosystems, including fire frequency, rainfall, browsing by herbivores, and atmospheric CO2
levels.
Step 2: Analyze the options.
- (A) Fire suppression can increase tree densities because fire is a key factor in limiting tree
growth in savannas. When fire is suppressed, tree densities can increase.
- (B) An increase in mean annual rainfall provides more water for tree growth, promoting an
increase in tree density.
- (C) Increased browsing by herbivores generally reduces tree densities by damaging or
eating the trees. Therefore, this option is not correct.
- (D) Increased atmospheric CO2 enhances photosynthesis and can lead to increased tree
growth, thus increasing tree densities.
Step 3: Conclusion.
The correct answers are (A), (B), and (D), as these factors all contribute to an increase in tree
densities in tropical savannas.