I have never bought wood for tanks, since I'm a cheapskate. We're an international group so there isn't always crossover on the species we can get, but for the UK and Canada it isn't wildly different.
All my wood and rocks come from where wood and rocks come from. I skip having someone else pick them up and ship them to stores.
I like to use oak and maple if I can. Elm also works (my neighbour has one of these now rare once common trees that offers tank decor after every gale). If I'm digging up shrubs or bushes, I have a look at the roots - often tree roots are very hard and last ages in tanks.
The best trees don't often offer the shapes we like though. I've learned to decorate without the twisty bits you find in imported tropical woods.
I'm surrounded by uncountable numbers of pines, and the temptation to try some of the interesting shapes I see is real. Resins are dangerous to a tank though. I have used pine that was bleached and dry from years off the living tree, but that's a rare find and has to be examined closely. Softwood, even if safe, decays in a tank. It shrinks in very little time. So it's not the best choice even if safe.
For all woods, I remove the bark. There is more likelihood of mould or fungus under when a tree's dead. It might be different for
@Colin_T in Australia, as fallen branches there won't go through a cycle of freezing and thawing.
I have used river driftwood, presunk and picked up as summer progresses and water levels drop. I just hose it off after I throw it in the kayak. I don't share the view that natural things are always a danger. Someone picked up that wood you pay for and hosed it before they threw it in a truck for the airport. Fish will clean it up, as long as you haven't foolishly taken it from a polluted river. Again, your environment matters. I'm surrounded by streams and forests that have been wrecked and modified by human activity, but not rendered toxic. Oaks were once common here, but the money was in softwood and they got in the way. They survive in the places where the logging companies don't spray for spruce budworm, and once you find those awkward spaces, you start looking. Some of the woods I've seen in the UK and the rest of Europe look like they've been planted by gardeners.
I prefer dry pieces, but they can languish in a bucket or bin with large water changes every few weeks for a year before they sink. Hardwood is slow to rot, but it's also slow to sink.
When I collect wood from the local creek overflow channel (a never-ending source for me), I look for pieces that are weathered and bleached enough to have lost all their bark. I usually scrub them nice and clean and lay them out in the sun several days to remove or kill any pathogens that might be on them.
