Wood (from All Over)

[ShoC]

hi,
I have a great time finding wood shapes I like,
but I do happen to live close to a woods.
what I'm wondering is Can I just go there find a totally dead piece of wood ( I mean proper dead)

Boil it etc.. and stick it in my tank?
are certain species of tree harmful? Eucalyptus being one that I could think off...

I have read Wolfs guide!
just think I might go for a walk if its okay to do so..