The forestry wiki does not specify. Is a redstone engine sufficient?
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Needs to be powered by a BuildCraft compatible engine... whatever that means – Ender Jan 11 '13 at 15:23
While I believe a redstone engine is indeed sufficient, you're probably going to want to juice it some more.
I've found that a Hobbyist's Steam Engine (2 MJ/t) (from Railcraft) performs well enough, but having at least a Commercial Steam Engine (4 MJ/t) (also Railcraft) is usually handy to get some real speed on the crafting.