Where is exponential growth by a plant population more likely - on a newly formed volcanic island or

For our summer work, we have a questions packet for the ecology unit of our textbooks that we have to complete.  I'm stuck on one of the questions about population growth -

Where is exponential growth by a plant population more likely - on a newly formed volcanic island, or in a mature, undisturbed rain forest? Why?

Doesn't it depend on whether the plant is iteroparous or semelparous? Wouldn't an iteroparous plant do better in a stable environment like the rainforest, while a semelparous plant would do better in an unpredictable environment, like the island?  Or does the fact that the island has nutrient-rich volcanic soil and (most likely) a lack of competing, parasitic, and predatory organisms make up for that?  I'm confused....