Thesis Abstract of AGS Students

Canopy Structure and Root Architecture in Miang-Based Agroforestry Systems

Sayan Tanpanich (1997)

The shortage of labour, insufficient fuelwood and declining in miang consumption among the young generation have forced the miang growers to adopt alternative land use. One of the alternative land use patterns which some farmers had already changed was miang-based agroforestry system.

The objectives of the study were to describe past and present land use patterns on the hilly areas where miang has been traditionally cultivated, to determine the canopy structure and root architecture among miang and selected tree components in miang-based agroforestry systems, and to assess production performance of the selected miang-based agroforestry system.

The study comprised of two parts, i.e., farmer interview and field study. Both of the studies were conducted at Ban Phadeng, Pa Pae sub-district, Mae Taeng district, Chiang Mai Province. The interview was carried out once before the field investigation in April 1996 and group interview in July 1997. The field study of canopy structure and root architecture was conducted at one farmer’s field during April to December of 1996.

There were three groups of miang farmers, i.e., those who had their own land, those who rented the land and miang pickers. The study showed that miang farmers were in the process of changing their land use patterns to include more diversified fruit tree species and rhetsa tree. The shortage of labour and fuelwood would limit miang production in the future.

Three land use patterns representing different developmental stages of miang-based agroforestry system were selected to study the canopy structure and root architecture. The methods of studying roots were proximal root geometry and fractal branching model. The canopy and root of each species and canopy and root arrangement in three stages were compared. The spatial analysis of canopy interactions were studied by using IDRISI, a raster Geographic Information System (GIS) software. The financial assessment in term of benefit-cost ratio (B.C. ratio) and net present value (NPV) were analysed.

Rhetsa had shown to be an important economic tree crop in the farm. The financial assessment among three stages indicated that the mature stage and the middle stage had the similar financial return but better than the early stage. However, all stages had B.C. ratio more than one.

Rhetsa was considered to be suitable for miang-based agroforestry system based on the above-ground criteria. The root of rhetsa was exploitative and explorative, required higher carbon input for maintenance, and was deeper than mango and pomelo. By above-ground criteria, marcotting mango and pomelo were more suited for miang-based agroforestry system than peach, direct seedling mango and jack fruit. Marcotting mango had wider crown width but shorter crown depth than pomelo. Pomelo and marcotting mango had similar root systems, but roots of pomelo condensed in the upper soil zone while root of mango penetrated in the deeper soil zone. The direct seedling mango was taller, and had greater crown depth and crown width than marcotting mango, as well as the root of direct seedling mango was more exploitative and explorative, and required higher carbon cost. The crown closure of marcotting mango when planted at 4 m apart reached each other at year nine. The root dry weight of mango increased with increasing age. The younger mango had finer root system and the root was bigger when mango was older until 8 years old. Mango grown in wider spacing gained more root dry weight than narrower spacing. The root of randomly-and-wide-space-planted miang and the row-planted miang occupied the medium soil zone, but the root of former planting arrangement was greater in exploitation, exploration and carbon cost for maintenance.

The mature stage plot showed the greatest overall above-ground and below-ground interactions while early stage plot showed the least. All stages were located in the sloping area which led to reducing root and canopy competition, however, the terracing practice tended to increase competition. The differences in root parameters of the upslope and downslope sides of the plants were not found. The recommended system of miang-based agroforestry systems, was rhetsa-pomelo-miang which planted in triangular arrangement.

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