Academic journal article Southeast Asian Studies

Factors Influencing Variations in the Density, Extent of Canopy Cover, and Origin of Trees in Paddy Fields in a Rainfed Rice-Farming Village in Northeast Thailand

Academic journal article Southeast Asian Studies

Factors Influencing Variations in the Density, Extent of Canopy Cover, and Origin of Trees in Paddy Fields in a Rainfed Rice-Farming Village in Northeast Thailand

Article excerpt

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Introduction

Paddy fields in Northeast Thailand are unusual in that they usually contain large trees. These fields are not just rice paddies but multi-resource systems providing a wide variety of goods and services to the rural people (Heckman 1979; Grandstaff et al. 1986; Rambo 1991; Patma 1993; Buared 2000). The trees provide food and medicine, firewood, lumber, small timber, non-timber products, and shade (Grandstaff et al. 1986; Buared 2000). They contribute organic matter to the soil (e.g., Sunee et al. 1992), which serves as a nutrient reserve and leads to higher cation exchange capacity (Patma 1993). Trees also provide fodder and shade to livestock as well as serve as habitat for various wild species, including insects, birds, and other animals (Grandstaff et al. 1986).

In recent years, however, in concert with other major changes associated with the ongoing agrarian transformation of Northeast Thailand-including the intensification of rice production, shift from subsistence-oriented farming to raising cash crops, mechanization, use of chemical fertilizers, and increased reliance of rural people on manufactured consumer goods-the role of trees in paddy fields has also been changing, leading to a general decline in tree density. However, only a few surveys have been made of the density of trees in paddy fields in Northeast Thailand and central Laos (ibid.; Watanabe et al. 1990; Buared 2000; Kosaka et al. 2006; Matsushita et al. 2011). They found a wide variation in number of trees per hectare, ranging from none to more than 150. A recent survey of tree density in paddy fields for the whole of the Northeast region revealed the mean density of trees in paddy fields was 12.1 trees/ha (Watanabe et al. 2014). In general, the northern part of the region has much lower densities of trees than the southeastern part. Density was found to be influenced by multiple factors: (1) the history of land development, with older fields displaying lower densities than newer fields; (2) topography, with fields located at higher positions in the toposequence having higher densities than those located in lower areas; (3) access to natural forest resources, with areas close to forests having higher densities than areas farther away; (4) amount of annual rainfall, with areas of higher rainfall having higher densities than areas of lower rainfall; and (5) landholding size, with areas of larger-sized landholdings having higher densities than areas of smaller-sized landholdings (ibid.). The kinds of crops planted in the paddy fields (in the past almost always rice but recently sometimes sugarcane or cassava) also influence density since trees reduce yields of shade-intolerant crops. Rice is more tolerant than field crops such as cassava and sugarcane, which leads farmers to cut down trees if they plant these field crops (Patma 2001). Although the degree of shading in fields is related to the extent of the trees' canopy coverage, no studies have been published on this aspect of trees in paddy fields.

The trees in paddy fields in Northeast Thailand have different origins: (1) forest survivors that have persisted from the original forest; (2) volunteers that have naturally generated from seeds brought into the system through various means; and (3) trees that were intentionally planted by the farmers (Patma 1993; 2001). Because tree management in paddy fields gradually evolves from a state of high tree density with little human care to one of low tree density with intensive human intervention, forest survivors come to be replaced by volunteers and planted trees with the passage of time (Grandstaff et al. 1986; Kosaka et al. 2006).

Although some studies conducted in Laos have described spatial variability in the occurrence of trees in paddy fields at both the community and plot levels (Kosaka et al. 2006; Matsushita et al. 2011), no systematic surveys of variability in tree density, canopy coverage, and origins of trees in paddy fields have been done at the community and plot levels in Northeast Thailand. …

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