I think you need to develop two important issues. Strucutral connectivity or fragmentation and functional connectivity or fragmentation. It might be there are proper habitats for amphibians in your forest yet you have no or little population and then you have to discover why. Then you have a suitable forest habitat with amphibians which means it is functional.
You please use GIS technology to identify the forest biodiversity health. In GIS atmosphere you can handle a lot of data-set with unimaginable results.