| dc.description.abstracteng | Around the globe, natural and agrarian landscapes are subject to agricultural intensification to meet the increasing and changing demands for resources of the growing population. This intensification takes place at two different scales: (1) At a landscape scale by reducing natural and semi-natural habitats to make room for the expansion of agriculture through monocultures and few crop types. (2) At a local scale, agricultural intensification implies shifts in agronomic practices such as the increasing application of agrochemicals, the use of heavy machinery, the cultivation of improved crop varieties and the reduction of genetic crop diversity. A decline of agrobiodiversity and associated ecosystem functions and services are one of the consequences, yet a changing agricultural system also impacts the social-ecological system. These transformations also affect small-scale and subsistence farming in the tropics. This thesis focuses on paddy cultivation systems in Wayanad district, Kerala State, South India and provides new results about effects of land-use change and agricultural intensification on agrobiodiversity and social-ecological processes.
In Wayanad, paddy cultivation has a very long tradition and is closely linked to the culture and religion of the inhabitants, especially in case of indigenous communities. However, traditional paddy cultivation is gradually intensified, mainly by the use of chemical fertilisers, insecticides and machinery as well as cultivation of high yielding varieties. Driven by the commercialisation of agriculture, paddy land has been and still is transformed to cultivate cash crops such as bananas, ginger, cassava or arecanut. Furthermore, increasing amount of semi-natural habitats such as homegarden polycultures is converted into simplified plantations.
For the ecological studies of the first and the second chapter of this thesis, we selected 18 paddy fields, which were cultivated by local farmers applying either high-intensity or low-intensity management. For the analysis, we focused on the three major agronomic practices, namely the amount of fertiliser application, insecticide application and weeding. Paddy fields were located either next to homegarden polycultures or banana monocultures. Samples were taken in three transects: (1) at the edge, close to adjacent habitat, (2) in the centre and (3) at the bund of the fields to consider possible edge effects. Additionally, we mapped the landscape components within a 500m radius around each field. The social-ecological study of the third chapter focuses on the three largest indigenous communities, the landowning agriculturalists Kuruma and Kurichya and the Paniya who are predominantly landless, agricultural labourer.
In the first chapter we analyse the response of paddy weeds, pests and predators to agricultural intensification at a local and landscape scale. Weeds, planthoppers and spiders were collected in the 18 paddy fields described above. The results showed that adjacent banana monocultures enhanced weed and planthopper population. Furthermore, the abundance of planthoppers was positively related to the density of weedy grasses but negatively affected by weed diversity (dominated by dicots). Spiders in contrast, benefited from weed diversity. However, spider population was mainly driven by prey availability. Increased fertiliser application had an indirect positive effect on spiders through increased prey abundance and weed richness. Spider abundance and richness decreased with increasing distance from the field edges, indicating influences of adjacent habitat on paddy field colonisation. The findings of this study suggest that paddy cultivation in Wayanad should consider the identity of adjacent habitat and weeds (monocots vs dicots) but also the amount of applied fertilisers to maintain a balanced agroecosystem.
The second chapter particularly focuses on the spider community in paddy fields. In addition to the abundance of the main spider families, we considered different web types as well as potential prey. Furthermore, effects of landscape characteristics and cultivation practices are taken into account. The analysis highlighted that the major determining factor for overall spider and web abundance was the prey availability; hence, the spider community in this paddy fields was driven by bottom up effects. A closer look at different families and web types revealed differences within this general pattern. For the web building Tetragnathidae and Linyphiidae Lepidoptera and leafhopper abundance were most important while Araneidae responded to Lepidoptera. The hunting spider Oxyopidae responded positively to Lepidoptera, leafhoppers and other insects. For this family we also found a slight negative effect of increasing herb cover in the paddy fields. The number of Salticidae and Lycosidae, also ahunting spiders, were only correlated with increasing numbers of Lepidoptera. Diverging results for web and spider abundances suggest that spider web sampling can be a useful complement to spider sampling. Furthermore, huge numbers of tetragnathid webs, which are easy to observe in the field, can be an indicator for the farmers to check their fields for possibly harmful infestation with rice pests.
In the third chapter, we focus on a social-ecological approach to assess the ecological knowledge and agricultural practices as well as the multiple meanings of social-ecological transformation processes. This qualitative study focused on the three major indigenous communities and their agrarian systems in Wayanad. We used three methodological tools, namely key informant interviews, village maps and seasonal calendars and focus group discussions. Central to this study was the development of a social-ecological web, which is understood as a bridging concept that integrates knowledge from social and natural science. This method is a useful tool to illustrate and compare the three different agrarian systems existing in Wayanad. Our results revealed that land-use change and intensification causes different degrees of social-ecological transformation among the three indigenous communities. Furthermore, the communities are affected by different factors of this change. For instance, the Kurichya's family structure remains largely unaffected so far while the Kuruma increasingly seek higher education and formal employment but deforestation negatively impacts livelihood strategies of the Paniya.
Overall, we argue that paddy agroecosystems in Wayanad were mainly driven by bottom-up effects: increasing resources led to an increase of individual numbers in higher trophic levels. Adjacent monocultures such as banana fields could enhance the population of rice weeds and pests. Intensification at the local scale had only minor effects, which may indicate that the intensification of paddy cultivation in Wayanad did not yet reached disastrous dimensions. Additionally, land-use change and agricultural intensification not only impact the ecological system, but also shape social-ecological transformation processes, which indicates the importance to examine such systems from an interdisciplinary angle. | de |