Depends on the trade, of course. But tradesmen work on different projects, travel to different areas, work with a range of skills.
I guess what I'm trying to say is that tradesmen != manufacturing plant worker.
I have a relative with a manufacturing plant. Their strategy is to try and out-niche the chinese. Their chinese competitors can dump finishing product onto the market cheaper than they can buy the raw materials. Thats' before the value-add of labour is included, with all the attendant taxes and benefits of the labour is paid for as well. The only way they can compete is to develop close relationships and fast turnarounds with their clients and hope like hell that's enough for them to ignore the price discrepancy. It generally depends on the final item being manufactured - anything competing in a fierce marketplace is going to go overseas at some point.
It's the unionised manufacturing sector worker that is getting smashed by low-cost foreign labour. And that is happening across all high-cost labour countries, Australia included.