In "The Sign of the Beaver", what is the adjoining land of another tribe?
The land adjoining that of the Beaver hunting grounds belongs to the Turtle Clan.
The Indians have a system of coexisting on the land based on mutual respect. They mark their hunting grounds with signs that are almost invisible to white men but clear in appearance and meaning to other Indians. When a tribe has marked an area as their hunting ground, other tribes will not take animals from that vicinity. Attean demonstrates this system to Matt on two occasions. The first is when he takes Matt deep into the forest to the beaver dam. The Sign of the Beaver has been carved into a tree near the dam, claiming the area for the Beaver Clan. When the young beavers at the dam are grown, the Attean's "family" will hunt there (Chapter 11).
The second occasion is when Matt and Attean come upon the trapped fox. Attean will not release the fox, because on a nearby tree the Sign of the Turtle Clan has been carved. If Attean were to release the fox, he would be taking an animal on Turtle land, and violating the clear code of respect for another tribe's hunting grounds (Chapter 13)