What might happen if people cut down the region's tropical or subtropical forest?

If all trees were cut down and burned, the forest's carbon storage capacity would be lost to the atmosphere. Some of this carbon would be taken up by the oceans, and some by other ecosystems (such as temperate or arctic forests), but no doubt this would exacerbate climate warming.

If the Amazon rainforest is destroyed, rainfall will decrease around the forest region. This would cause a ripple effect, and prompt an additional shift in climate change, which would result in more droughts, longer dry spells, and massive amounts of flooding.

fertilization is the union of an egg and a sperm cell i believe.