This would only apply if the tribal govt. is requesting separately from the state.
All land within the limits of an Indian reservation that is under the jurisdiction of the US govt, all dependent Indian communities and all allotments still in trust, located on or off reservations are generally areas where tribal sovereignty applies. These areas can be located in multiple states and often not contiguous. Just as counties affected by an event are designated, it stands to reason that tribal leadership will request designation for all Indian or Native Alaskan land that has been affected by the same event. For example, one storm system may pass through several parcels belonging to a tribal govt.-- or just one parcel. If an event affects a reservation, the entire reservation can be designated. If trust lands for the same tribal govt. were not affected, they would not be designated. As with State govt, only affected counties are designated, and within those designated counties, only those who were affected (individuals, businesses, public infrastructure, etc) may be eligible.