Article about rainforests

If the story is correct, botanists brought not "botanical scrap", but essential elements from other tropical rain forests.

"But in 1843, an ambitious British scheme for revitalising the island began, with Royal Navy troops planting thousands of trees a year, using seedlings from Argentina, South Africa, and the Royal Botanical Gardens at Kew."

Hardly random. In different rain forests, different species can have the same niche and functions, and these often can be interchanged.
Not everything survived, but those that could survive with each other, did.

People resist the idea that plants can "behave" differently in different environments, but it's true. The fact that the forest works as it is, does not mean that if more evolved species were to be introduced, they would not replace some of the less-evolved plants that currently occupy these niches. Indeed, Oldenlandia adscensionis, the only woody shub found on the island when it was discovered, has suffered just that fate, and is now thought to be extinct.

We have seen just that happen in a number of cases where plants were brought to oceanic islands.

Far from being a "random" introduction of plants, this was a conscious and scientific effort to create an ecosystem. Botanist Joseph Hooker, at the request of the British Navy, submitted a plan do just that. Simplified, it was:

1. Planting trees on the mountain which he considered ‘of the first importance as thereby the fall of rain will be directly
increased’

2. Developing the formation of deeper soils by encouraging more vegetation to grow on the steeper slopes.

3. Planting the more promising areas in the lower valleys with drought adapted trees and shrubs.

4. Introducing suitable crops into gardens on Green Mountain.
http://www.staff.livjm.ac.uk/biedwilk/pdfs/greenmt.pdf

I admit I enjoy those "even scientists are baffled" stories. Takes me back to my early teens, when I loved giant insect movies.