That's where we need to look at stress relief? When we try to decide what species a found wood might be, it can be really hard. When a tree is living we have to use all kinds of small hints to get down to the exact type of tree. We look at bark, leaves, acorns, and even where it is growing. Not hard to tell an oak from a cedar! But all that is gone when wood has been dead and out in the weather for a long time. So we can make life a lot easier if we forget the worry about what species. We often can't tell anyway.
What we should worry about is how dry the wood is rather than the species. But then that can be an easy point to miss if we don't know what to look for in the wood.
We can get by with using wet wood if we don't mind fighting with tannins but why bother?
If we use totally dry wood, it should have no bark left, be lighter weight for the size and have a pretty uniform color all the way through.
This is a big piece of cedar I use as an example of totally dry wood.
It is cedar or juniper but when I cut it open to make space for fish, I find a uniform color except around knots where the sap is often a bit slower.
Totally safe to use when the wood is dry. I used this for spawning sites for rainbow cichlids.