Good question. That gives me an idea for a future post to help people to determine if a branch is dead or not when there are no leaves. It can be very hard to know. Recently I made a mistake on a tree by trimming off a branch I thought was dead, and it was actually still green wood inside the cut. Oops! Sometimes I find out after I made the cut, I guessed wrong. If I studied the tree better, I probably would not have made that mistake.
Here is a discussion I had recently in the comments that might answer your question a bit more in depth...
Question Answered: How do you decide which branches to prune?
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