Māori have distinct systems, customs, and beliefs regarding their relationship to the land and other resources, as well as to each other. Prior to European settlement and the signing of the Treaty of Waitangi, the individual Māori tribes had well-established governance arrangements, social structures, and systems of customary protocols, referred to as tikanga Māori. This included rules relating to trade and land rights, family relationships, protection of the environment, and conflict resolution.
In addition to claims relating to obligations in the Treaty of Waitangi and those that arise through legislation, Māori customary law may be recognised within the New Zealand common law system through the doctrines of aboriginal rights and aboriginal title. Under the doctrine of aboriginal rights, customary laws or practices of a continuous nature may be granted the force of law by the courts and any associated rights enforced if they have not been extinguished by statute. See Huakina Development Trust v Waikato Valley Authority HC Wellington M430/86  NZHC 130;  2 NZLR 188, in which the Court held that 'customs and beliefs are capable of being established on evidence by the courts'. On the doctrine of aboriginal title, see, for example, Aboriginal & Treaty Rights In Aotearoa - NZ, which links to relevant cases.
For a good summary of Māori customary law, and the legislation enshrining or affecting it, see the Library of Congress' Legal Research Guide: Māori Customary Law.