Brontomek

The planet Arcadia was on the verge of economic collapse. Its human colony had been decimated by the strange Relay Effect; in the aftermath, still more colonists were leaving for other worlds. The Hetherington Organisation promised to change that. If the remaining colonists put themselves entirely in their hands for a five-year period, they would transform Arcadia into the most prosperous planet settled by mankind, while preserving its great natural beauty.
It was an offer the Arcadians could not possibly refuse, for the alternative, after all, was an accelerating slide into poverty and, eventually, savagery. Only when the Hetherington Organisation's first cargo ships arrived, unloading a huge stream of brontomeks - huge robot agricultural machines, heavily armoured - and an army of amorphs, aliens who were capable of moulding themselves into human form, did the colony begin to realise what it had committed itself to.
Brontomek! is a sequel to two earlier books, Syzygy and Mirror Image. Like it's predecessors it is an ingenious, adventurous tale of the type which has rapidly made Coney one of SF's foremost entertainers. Brontomek! won the 1977 BSFA award for best novel.