In my experience, dried oak leaves and magnolia leaves don't break down rapidly. Neither grows here, so I have to import them from friends. They do indeed seem to increase the boldness of usually shy frogs like the blue auratus, which can dive under a nearby leaf when they feel threatened. Do avoid pineneedles, as these may still contain some turpentines that may be a bit toxic, as well as litter from cedar.
I also agree that the only problem with leaf litter would be with pesticides. You may get some bugs that you don't particularly like, such as centipedes, but these won't hurt your frogs, and they do a good job of recycling. The other possible problem might be with slugs, but if you dry it out well before adding them, this reduces the chance of introducing slugs.
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Patty
Pahsimeroi, Idaho
4 D. auratus blue
5 D. galactonotus pumpkin orange splash back
5 D. imitator
6 D. leucomelas
4 D. pumilio Bastimentos
4 D. fantasticus
4 P. terribilis
4 D. reticulatus
4 D. castaneoticus