Gardening Australia

I've got a wattle that currently has a thinner than ideal trunk. I've been looking into what I can do to encourage it to develop a thicker trunk. Mostly this seems to be about only providing the minimum amount of support it needs and keeping it loose so that the wind / swaying stimulates trunk growth.

But in passing I've heard that trimming the lower branches can also help. So far this is just a rumour to me and I'd like to substantiate it somehow. Have others heard the same?

Also - with the heat we're getting lately do I need to worry about stressing out the tree? I probably don't need to remove that many branches (should be less than 10%). Is there a good guide for how much I can trim without stressing the tree?