Darwin was not the man to make observations only and he thought that the water supply might be augmented if the volcanic peaks could have a more or less permanent cloudy crown such as he'd seen on numerous tropical islands in the Pacific. One difference between Ascension and, say, Tahiti was that the latter had a rain-forest. Maybe if you built a forest, rain would come? Darwin was not the first man to voice such an idea but he was remarkably well connected to the scientific-political establishment. When he returned to England he shared this idea and his enthusiasm for it with his pal Joseph Hooker, whose father was director of the botanic garden in Kew. Hooker made his own 'site-visit' to Ascension in 1843 on his way back from a famous Antarctic exploration and could only identify a single species that passed as a tree. At the behest of the Admiralty, Hooker undertook to ship a variety to trees, shrubs and understory plants to Ascension to a) encourage aforestation to promote clouds and rainfall b) to stablise steep inclines and slow run-off c) try out a few xerophytes that would tolerate the prevailing salt-arid conditions and finally d) provide some fresh food for the garrison. Everything had to be proof against goats, rats and mice which had been introduced since the island was discovered in 1502. The species sent out were chosen using the best scientific information that could be obtained. Survival was a bit of a lottery: some seeds and saplings got the mildew aboard ship; others were eaten by the goats and some wouldn't have made it anyway for various unfathomable genetic or ecological imperatives. In all of this, nobody paid the slightest heed to the existence or well-being of the microbial flora surrounding the roots of the imports.
introducing wolves to Yellowstone, we have a matching disaster like bringing rabbits and cane-toads to Australia or goats+rats+cats pretty much everywhere a sailor has ever set foot.