Plant community composition and biodiversity of irrigated rice ecosystems in Vietnam and the Philippines
by Oliver Fried
Date of Examination:2021-07-01
Date of issue:2021-11-26
Advisor:Prof. Dr. Erwin Bergmeier
Referee:Prof. Dr. Erwin Bergmeier
Referee:Prof. Dr. Teja Tscharntke
Referee:Prof. Dr. Hermann Behling
Referee:Prof. Dr. Catrin Westphal
Referee:Prof. Dr. Ralph Mitlöhner
Referee:Prof. Dr. Johannes Isselstein
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Description:Dissertation
Abstract
English
Irrigated rice landscapes in tropical and subtropical Asia are complex agroecosystems that have evolved mostly from natural wetlands. Millennia of interaction between human communities and their surrounding ecosystems have shaped these highly-dynamic and diverse environments that provide several valuable ecosystem services and host a diversity of plants, animals and habitats. However, this biodiversity is threatened by ongoing agricultural intensification and the conversion of vast farmland areas to monoculture crop production. Besides, the knowledge on the diversity and composition of plants in rice ecosystems and the occurring rice weed communities is still inadequate. This thesis aimed at a more comprehensive understanding of the diversity, composition, dynamics and distribution of rice weed communities in important rice-producing regions of Southeast Asia. Research focused on seven regions in Vietnam and the Philippines which are greatly varied in terms of climate, edaphic conditions, landscape heterogeneity, agricultural management and biodiversity. I examined two major habitat types of rice ecosystems, i.e. paddies (the field proper) and bunds (or levees), to reveal their plant diversity, the prevailing life forms, the plant communities, and the main environmental drivers and phytogeographic patterns that shape these communities. In the introductory chapter, the importance of rice ecosystems and the origin and history of rice cultivation are discussed. Further, I inform on the nature of these agroecosystems by providing details on the biology of the rice plant, the ecology and composition of rice environments, and the significance, diversity and control of rice weeds. The chapter ends with a closer look on the study area and the general description of applied methods. The second and the third chapter give information on the composition of plant species and prevailing life forms on local paddies and bunds, respectively. The descriptions are complemented by recorded (and in the case of paddies also projected) levels of species richness to provide a comprehensive picture of the floristic diversity of the rice ecosystems in total, in each region, in uplands and lowlands, and in the two countries. The two studies identify the main rice weed communities in paddies and on bunds, and provide details on their differential species, geographic distribution, plant diversity, time of emergence during the crop cycle, as well as the abiotic conditions under which they occurred. In the fourth chapter, the effects and relative importance of abiotic conditions, habitat type and surrounding landscapes on the plot-level plant diversity (alpha diversity) in the seven study regions are investigated and presented in a comparative overview. Another main objective of the study in this chapter is the quantification and visualization of the species turnovers (beta diversity) across sampling sites, between paddies and their bunds, and between regions. The fifth chapter summarizes the major findings of the thesis to highlight the differences and similarities of bunds and paddies in terms of floristic diversity, the composition of species and life forms, the community variation along environmental gradients, and applied weed control measures and cultivation practices. I conclude that our results provide new insights into the composition and functioning of rice landscapes, and indicate remaining issues. The findings offer interesting opportunities for biodiversity conservation, ecological engineering approaches and the sustainable management of rice ecosystems.
Keywords: agroecosystem; bunds; Oryzetea sativae; paddy; plant life form; rice field; species richness; species turnover; weed community; weed control