At least six ethnic groups of highland people live in the North of Thailand. They are the Karen, Hmong, Mien, Lahu, Lisu, and Akha. Some of these groups practiced rotational swidden agriculture, which required them to move the sites of their fields approximately every ten years but not their villages. Others groups practiced swidden agriculture without rotational use of their field. They moved to a new site approximately every decade after the fields have degraded.