Let's see what plants need to survive:
0. Water
,
1. Sunlight
,
2. Nutrients
,
3. Soil
Plants that live around each other also will compete for resources, since there is only so much water and area on this planet. We know that trees can block ground vegetation from getting sunlight. Plants close to each other also steal each other's nutrients and water as well.
Therefore, we are left with one answer choice that is correct: warmth.
Weather and climate affects all living organisms in an biome.