Effects of double rice cropping with irrigation on the diversity of herbaceous plants and their utilization as a food source in paddy fields of southern Lao People’s Democratic Republic

Herbaceous plant diversity including rare aquatic species has been lost in many countries by agricultural intensification and abandonment. In paddy fields of the Lao People’s Democratic Republic (Lao PDR), irrigation facilities have been constructed rapidly since 1997. The aim of this study was to clarify the impacts of double rice cropping accompanied by the introduction of irrigation systems on herbaceous plant diversity and utilization in paddy fields of southern Lao PDR. Ground vegetation surveys and interviews were conducted in Kok Deau and Lak 30 villages in Champasak Province, and propagule bank survey was conducted in Kok Deau village. The species richness and species diversity, measured by the Shannon’s diversity index, were not significantly different between the irrigated and rainfed paddies (p?>?0.05), when compared in both the wet and dry seasons. However, double rice cropping with irrigation systems affected herbaceous plant species composition in paddy fields. Increased use of chemical fertilizers in irrigated paddies resulted in predominance of tall undesirable species, such as Fimbristylis miliacea (L.) Vahl and Echinochloa colona (L.) Link. Small and frequently submerged species were dominant in the ground vegetation and propagule banks of the rainfed paddies. Since small submerged species are often sensitive to environmental changes, increase of irrigated paddy area may lead to a decrease in the variety of aquatic herbaceous plants in Lao PDR. While a total of 9 herbaceous plant species were utilized as foods in the villages, no change was recognized by farmers in species composition and frequency of utilization of paddy plants as food before and after the development of the irrigation systems.

     

Uses of trees in paddy fields in Champasak Province, southern Lao PDR

The species and uses of trees located in paddy fields were investigated in three villages in Champasak Province, Lao PDR. The villages were different in their distance from Pakse City, the capital of the province, and age since foundation. A total of 71 species were recorded, and most were used by local people. The most frequent use was for fruit, firewood, and medicine, though most trees also offered shade for cattle and people. Species composition differed among villages. The youngest paddy supported more trees, remnants of the original forest, for timber. Older paddies supported fewer trees for timber but more for fruit and firewood. The introduced species increased according to the age of the paddy. Products other than timber obtained from the trees were common among villages. The significance of trees in rice cultivation in Laos was compared with that in the Satoyama landscape of Japan.