Rice farming is the main economic activity of inhabitants of the upper plains. These communities consist of farming groups who cultivate rain-fed or irrigated rice paddies. They tend to live in small family groups or villages. In general, each family cultivates a field prepared by slash and burn techniques, where rice, cucumbers, occasionally corn, and other vegetables are grown. Usually a number of different traditional varieties of rice are grown, each one adapted to different soil types and water conditions. The farmers use animal fertilizers and traditional farming techniques, such as the swing plow pulled by oxen or buffalo.The sugar palm is the national tree of Cambodia. These trees dominate the Cambodian landscape, and most of them grow in rice fields or thicker forest groves. The valuable by-products of the sugar palm include sugar, palm wine, seeds which can be eaten as dessert, timber, and the fronds, which can be used in weaving.