Distribution patterns of trees in paddy field landscapes in relation to agro-ecological settings in northeast Thailand

Abstract

Deforestation accompanied by the expansion of agricultural land makes tree resources less available in many regions in the tropics, and small-scale farmers often incorporate trees with agricultural lands to meet their demands for food, timber, fuelwood, or fodder. This study analyzed the distribution patterns and management of multiple tree species grown in the rice paddy fields of a forest-depleted region in northeast Thailand – a region whose forestland represents only 16.32% of the total land area. Twenty villages from 11 provinces were selected for the remote sensing analysis of tree density and microhabitat. Interview surveys were conducted among villagers on their tree use and management, and field observations were performed to determine tree species’ composition. The average tree-unit density (based on the number of tree crowns, either of a single tree or of cohesive trees, appearing in satellite images) was 6.27units/ha, and was correlated with both density on the levee (5.30units/ha on average) and levee length per unit paddy area (475.25m/ha on average). The levees were more significant as tree habitats in the villages on the floodplain where the early introduction of agricultural machinery and direct seeding reduced the number of trees inside the fields where rice crops are grown. In total, 79 tree species representing 66 genera and 33 families were observed in the paddy fields. Remnant trees from the original forest, mostly Dipterocarpaceae and Fabaceae, have decreased due to cutting for use as timber and fuel. More recently, eucalypt and teak for timber, and mango and tamarind for edible fruits, have been planted on the levees as income sources. Farmers have recognized that while leaf litter fertilizes the soil, excess shading reduces the rice yield. The coppicing of eucalypt and pollarding of Mitragyna diversifolia were conducted for the sustainable harvest of timber and fuelwood, and also to avoid creating excess shade. Paddy rice fields are the monoculture of a staple crop, but they can harbor multiple trees on their levees, which play a counteractive role in forestland decline.