Reproduced, with permission, from:In northeast Thailand trees are a common sight in rice fieldsor along their borders. Grandstaff et al. (1986) observed that many such species occurred in the forests covering the land before it was converted to agricultural use.
There are four stages in the conversion of forest to rice land. In the first stage, many trees are spared during clearing. Large numbers grow in the fields and on the dikes. They are continuously thinned and used for timber. In the second stage, the old trees still grow in the fields, but farmers do not especially promote tree growth because forests still provide wood.
In the third stage, natural sources of wood have become scarce and seedlings springing up on the field dikes are increasingly protected and are planted. In this stage trees are not grown for timber because of the long delay before they can be so used, but are intended for shade, food, fodder and other uses. Ton sio (Phyllanthus polythyllus), for example, is preferred because its dense roots help hold the dikes and because its sparse foliage does not provide too much shade (Grandstaff et al. 1986:287-288).
In some regions, old large trees, reminiscent of the original forest and useful for lumber, are preserved for the farmers' descendants, even though they may be in the middle of the field and need heavy pruning (Grandstaff et al. 1986:280). In stage four, the forest has been completely replaced by rice. Few trees are found in the fields; nearly all of those on the dikes and mounds have been planted. Farmers say that the trees do not harbor insects harmful to rice but that birds may be a serious pest (p. 287).
Some 50 tree species grow in rice fields in northeast Thailand. Considering the importance farmers in this region attach to trees, these authors wonder why farmers in other areas of the country do not plant trees in their rice fields. Grandstaff et al. suggest that topography, soil type, climate and other physical factors favor tree growing in the Northeast and may make it more difficult and expensive to establish trees in other areas.