Failed attempts at changing ecosystem in order to preserve it?
Perhaps not quite what you had in mind, but it seems like the introduction of the mongoose into Hawaii is close. In the late 19th century sugar planters introduced mongooses into Hawaii in an attempt to control rat populations. It turns out that rats are mostly nocturnal, and mongooses are mostly diurnal, so the two species rarely interacted. The mongoose population boomed and had a huge negative impact on native bird and turtle populations, since the mongooses would eat the bird and turtle eggs.