in my experience, ask. The park may appreciate or not what is considered trimming.
In many camps there is a sensible rule against firewood gathering, in others its encouraged.
Never have we seen a camp allow tree trimming without permission. A limb thats looks low for you might be left that way for the health of the tree or shade.
My camp has only Raspberry and Gooseberry bushes left, due to thier thorny and crooked nature which makes them useless for wiener sticks.
Don't cut without asking