I think a tree holding a hill in place is more a factor of soil, root structure & precipitation than the wood strength. Shallow roots, loose soil: not gonna hol

I think a tree holding a hill in place is more a factor of soil, root structure & precipitation than the wood strength. Shallow roots, loose soil: not gonna hold much. Deep roots, compacted or rocky soil: basically reinforced concrete. Whether it's more dry or waterlogged probably changes it too. Also, if the tree grew slanted, it would actually be unusually strong in that position compared to a tree that was shifted into that position.