2013

Hardeweg, Bernd, Andreas Wagener and Hermann Waibel (forthcoming): A distributional approach to comparing vulnerability, applied to rural provinces in Thailand and Vietnam. Journal of Asian Economics.

Hardeweg, Bernd, Lukas Menkhoff and Hermann Waibel (forthcoming): Experimentally validated survey evidence on individual risk attitudes in rural Thailand economic development and cultural change. Economic Development and Cultural Change.

Lohmann, Carsten and Ingo Liefner (forthcoming): Spatial patterns of private sector and public sector non-agricultural jobs in rural Northeast Thailand. Regional Studies. Download

2012

Amare, Mulubrhan, Lena Hohfeld, Somchai Jitsuchon and Hermann Waibel (2012): Rural–urban migration and employment quality: A case study from Thailand. Asian Development Review. Vol. 29 (1). p. 57-79. Download

Menkhoff, Lukas, Doris Neuberger and Ornsiri Rungruxsirivorn (2012): Collateral and its substitutes in emerging markets’ lending. Journal of Banking & Finance. Vol. 36 (3). p. 817-834. Download

2011

Chiwaula, Levison S., Rudolf Witt and Hermann Waibel (2011): An asset-based approach to vulnerability: The case of small-scale fishing areas in Cameroon and Nigeria. Journal of Development Studies. Vol. 47 (2). p. 338-353. Download

Menkhoff, Lukas and Ornsiri Rungruxsirivorn (2011): Do village funds improve access to finance? evidence from Thailand. World Development. Vol. 39 (1). p. 110-122. Download

Gödecke, Theda and Hermann Waibel (2011): Rural-urban transformation and village economy in emerging market economies during economic crisis: Empirical evidence from Thailand. Cambridge Journal of Regions, Economy and Society. Vol. 4 (2). p. 205-219. Download

2010

Witt, Rudolf, Diemuth Pemsl and Hermann Waibel (2010): Collecting data for poverty and vulnerability assessment in remote areas in Sub-Saharan Africa. Survey Methodology. Vol. 36 (2). p. 217-222. Download

Völker, Marc and Hermann Waibel (2010): Do rural households extract more forest products in times of crisis? Evidence from the mountainous uplands of Vietnam. Forest Policy and Economics. Vol. 6 (12). p. 407-414. Download

2009

Günther, Isabelle and Ken Harttgen (2009): Estimating households' vulnerability to idiosyncratic and covariate shocks: A novel method applied to Madagascar. World Development. Vol. 37 (7). p. 1222-1234. Download

Lohmann, Carsten and Ingo Liefner (2009): Location, non-agricultural employment and vulnerability to poverty in rural Thailand. Erdkunde. Vol. 63 (2). p. 141-60. Download

 

2012

Klasen, Stephan and Hermann Waibel (Eds.) (2012): Vulnerability to poverty: Theory, measurement and determinants, with case studies from Thailand and Vietnam. Palgrave Macmillan, 360p. Contents

Kemper, Niels, Rainer Klump, Lukas Menkhoff and Ornsiri Rungruxsirivorn (2012): Financial and other smoothing mechanisms in rural Thailand and Vietnam. In: Klasen, Stephan and Hermann Waibel (Eds.): Vulnerability to poverty: Theory, measurement and determinants, with case studies from Thailand and Vietnam. Palgrave Macmillan, Hampshire, United Kingdom.

Klump, Rainer, Javier Revilla Diez and Kai Mausch (2012): Rural Vietnam: Pro-poor growth vs income structure. In: Klasen, Stephan and Hermann Waibel (Eds.): Vulnerability to poverty: Theory, measurement and determinants, with case studies from Thailand and Vietnam. Palgrave Macmillan, Hampshire, United Kingdom.

Gödecke, Theda (2012): Research on vulnerability to poverty: A village case study from Thailand. Dissertation. Institut für Entwicklungs- und Agrarökonomik, Leibniz Universität Hannover, Germany, 147 p.

Chichaibelu, B. B. and H. Waibel (2012): Financial vulnerability and indebtedness of poor households in Thailand and Vietnam. Poster and paper presented at Tropentag 2012: Resilience of agricultural systems against crises. September 19-21, Göttingen, Germany. Download

Hohfeld, L. and H. Waibel (2012): Is there a future for agriculture in rural villages in Northeast Thailand? Poster and paper presented at Tropentag 2012: Resilience of agricultural systems against crises. September 19-21, Göttingen - Kassel/Witzenhausen, Germany. Download

Gödecke, T. and H. Waibel (2012): Understanding social networks in rural Thailand. Poster presented at Jahrestagung 2012 "Development Economics and Policy" of Ausschuss für Entwicklungsländer (AEL) of Verein für Socialpolitik. June 22-23, Bonn, Germany. Download

Duc, Tung Phung (2012): Vulnerability to Poverty in Rural Vietnam: Data Collection Issues, Coping Strategies and Crisis Events. Dissertation. Institut für Entwicklungs- und Agrarökonomik, Leibniz Universität Hannover. LAP Lambert, Saarbrücken, Germany, 188 p.

Povel, Felix (2012): Poverty and vulnerability in Southeast Asia. Dissertation, Georg-August-Universität Göttingen. Optimus, Goettingen, 147p.

2011

Gloede, Oliver, Lukas Menkhoff and Hermann Waibel (2011): Risk attitude and risk behavior: Comparing Thailand and Vietnam. Working Paper. Download

Kemper, Niels, Rainer Klump and Heiner Schumacher (2011): Representation of property rights and credit market outcomes: Evidence from a land reform in Vietnam. Working Paper, presented at Verein für Socialpolitik, Frankfurt, Session: Credit and Insurance in Developing countries. (with Kristina Czura, Goethe University, and Ingo Outes, University of Oxford), 2011; Second European Research Conference on Microfinance, Groningen, Netherlands, 2011; Eighth Midwest International Economic Development Conference, University of Wisconsin-Madison, Madison, USA, 2011; and Verein für Socialpolitik (Entwicklungsländerausschuß), Berlin, 2011.

Kislat, Carmen and Lukas Menkhoff (2011): The village fund loan: who gets it, keeps it and loses it? Working Paper, presented at the 43rd Annual International Conference of the Money, Macro and Finance Research Group (MMF), September 15-17, Birmingham, UK. Discussion paper of the Faculty

Klasen, Stephan, Tobias Lechtenfeld and Felix Povel (2011): What about the Women? Female headship, poverty and vulnerability in Thailand and Vietnam. Courant Discussion Paper No. 76, University of Göttingen, Göttingen, Germany.

Ligon, Ethan and Felix Povel (2011): Eliciting subject’s prediction of shocks in Thailand and Vietnam. Working paper, University of California, Berkeley, and University of Göttingen, Germany.

Povel, Felix (2011): Vulnerability to downside risk. Working paper, University of Göttingen, Germany.

Schmid, Dominik (2011): Der ländliche außerlandwirtschaftliche Sektor in Thailand und Vietnam - Struktur, Krisenanfälligkeit und institutionelles Umfeld. Dissertation, Justus-Liebig-Universität Gießen.

Tongruksawattana, Songporne (2011): Response of rural farm households to income shocks. Dissertation, Leibniz Universität Hannover.

Vu, Thi Hoa (2011): Farm size and productivity: Empirical evidence from Rural Vietnam. Diploma Thesis, Institut für Entwicklungs- und Agrarökonomik, Leibniz Universität Hannover, Germany.

2010

Chiwaula, Levison S. and Hermann Waibel (2010): Extent and impacts of household seasonal vulnerability to poverty: A case study from the Hadejia-Nguru Wetlands in Nigeria. European Association of Agricultural Economists (EAAE). November 25-27, Hohenheim, Germany. Download

Duc, Tung P. and Hermann Waibel (2010): Diversification in land and labor allocation in response to shocks among small- scale farmers in Central Vietnam. Schriften der Gesellschaft fur Wirtschafts- und Sozialwissenschaften des Landbaues e.V. Vol. 45, p. 91-111. Download

Gloede, Oliver and Ornsiri Rungruxsirivorn (2010): Financial development and household welfare: Microevidence from Thai Households. Working Paper. Download

Hardeweg, Bernd, Andreas Wagener and Hermann Waibel (2010): Towards comparative and aggregate vulnerability: Analysis of welfare distributions in rural areas in Thailand and Viet Nam. Paper presented at Jahrestagung des Vereins für Socialpolitik. September 7-10, Kiel, Germany. Download

Hardeweg, Bernd, Lukas Menkhoff and Hermann Waibel (2010): Experimentally-validated survey evidence on individual risk attitudes in rural Thailand. Paper presented at 25th Annual Meeting of the European Economic Association. August 23-26, University of Glasgow, Scotland; and at Annual Conference of the Royal Economic Society. March 29-31, University of Surrey, Guildford, UK. Download

Hohfeld, Lena (2010): Rural urban migration and agricultural investment. Poster presented at Tropentag 2010: World food system - A contribution from Europe. September 14-16, Zurich, Switzerland. Abstract

Kay, Katharina (2010): Ethic minorities and agricultural commercialization in Dak Lac, Vietnam. Diploma Thesis, Institut für Entwicklungs- und Agrarökonomik, Leibniz Universität Hannover, Germany.

Kemper, Niels and Rainer Klump (2010): Shock-coping and household finance in rural Vietnam: Evidence and some implications. In: Morelli, Emanuela, Amsicora Onnis, Walter Ammann and Corina Sutter (Eds.): Microinsurance: An Innovative Tool for Risk and Disaster Management. GRF, Davos. p. 269-297.

Maeurer, Nicolai (2010): Vulnerability and climate change in South East Asia: A literature review. BA Thesis, University of Göttingen, Göttingen, Germany.

Mausch, Kai (2010): Poverty, inequality and the non-farm economy: The case of rural Vietnam. Dissertation, Leibniz Universität Hannover.

Povel, Felix (2010): Perceived vulnerability to downside risk. Courant Discussion Paper No. 43, University of Göttingen, Germany.

Povel, Felix (2010): Vulnerability to downside risk and poverty in Vietnam. Courant Discussion Paper No. 44, University of Göttingen, Germany.

Völker, Marc (2010): Mountain agriculture, natural resource extraction and risk perception: Determinants of vulnerability to poverty in rural Vietnam. Dissertation, Leibniz Universität Hannover.

2009

Dietrich, Antje-Mareike (2009): Female-headed households and poverty - Empirical results from Thailand and Vietnam. BA Thesis, Georg-August-Universität Göttingen, Germany.

Gummert, Knut (2009): Impact of shocks on households’ well-being in Thailand and Viet Nam. Diploma Thesis, Georg-August-Universität Göttingen, Germany.

Pilaiwan Boonsin (2009): Farming diversity and the vulnerability to poverty of households in Buri Ram. Master Thesis, Kasetsart University, Bangkok, Thailand.

Supanika Chanawirat (2009): Non-farm income and the vulnerability to poverty of households in Ubon Ratchathani Province. Master Thesis, Kasetsart University, Bangkok, Thailand.

Voraus Chevachaipimol (2009): Natural resources product utilization and vulnerability to poverty in Nakhon Phanom Province. Master Thesis, Kasetsart University, Bangkok, Thailand.

Lohmann, Carsten (2009): Außerlandwirtschaftliche Beschäftigung im ländlichen Thailand: Ursachen, Auswirkungen und Zugangsfaktoren. Dissertation, Justus-Liebig-Universität Gießen. Nomos, Baden Baden. Download

Rungruxsirivorn, Ornsiri (2009): An empirical analysis of rural finance and its impacts on household vulnerability in Thailand. Dissertation, Leibniz Universität Hannover. Download

Klasen, Stephan and Isabelle Günther (2008): Measuring chronic non-income poverty. In: Addison, Tony, David Hulme and S.M. Ravi Kanbur (eds.): Poverty dynamics: interdisciplinary perspectives. Oxford University Press.

Witt, Rudolf, Levison S. Chiwaula and Hermann Waibel (2009): Vulnerability and household livelihoods in small-scale fishing areas in Nigeria and Cameroon - An asset-based approach. Inaugural Conference of the Courant Research Centre 'Poverty, Equity and Growth'. July, 1-3, Göttingen, Germany.

Tongruksawattana, Songporne, Erich Schmidt and Hermann Waibel (2009): Shocks and coping strategies of agricultural households: First results from three provinces in Thailand. Paper presented at the Workshop of Research Unit 756 of the Deutsche Forschungsgemeinschaft (DFG). February 22-26, Hue City, Vietnam. Download

Menkhoff, Lukas and Ornsiri Rungruxsirivorn (2009): Village Funds in the rural credit market of Thailand. Paper presented at the Workshop of Research Unit 756 of the Deutsche Forschungsgemeinschaft (DFG). February 22-26, Hue City, Vietnam. Download

Kemper, Niels, Rainer Klump, Lukas Menkhoff and Ornsiri Rungruxsirivorn (2009): Financial and other shock-coping mechanisms in rural Thailand and Vietnam. Working Paper Download

Hardeweg, Bernd and Hermann Waibel (2009): Collecting data to measure vulnerabilty to poverty: An overview. Paper presented at the Workshop of Research Unit 756 of the Deutsche Forschungsgemeinschaft (DFG). February 22-26, Hue City, Vietnam. Download

Hardeweg, Bernd and Hermann Waibel (2009): The spatial distribution and interregional dynamics of vegetable production in Thailand. Poster presented at 49th Annual GEWISOLA Conference 2009. September 30 - October 2, Kiel, Germany.

2008

Witt, Rudolf, Diemuth E. Pemsl and Hermann Waibel (2008): Small-scale inland fisheries in Africa: How to collect data for poverty assessment? Paper presented at Annual Conference of "Verein für Socialpolitik: Research Committee Development Economics". May 30-31, Zürich.

Rungruxsirivorn, Ornsiri (2008): Village heterogeneity and consumption smoothing: empirical evidence in Thai villages. Working Paper. Download

Liefner, Ingo and Carsten Lohmann (2008): The spatial dimension of vulnerability to poverty - First results from a household survey in rural Thailand. Conference Proceedings of the 8th Regional Science Association International - World Congress, March 17-19, 2008, Sao Paulo, Brazil. ISBN: 978-85-61522-00-1. Download

2007

Hardeweg, Bernd, Hermann Waibel, Suwanna Praneetvatakul and Tung P. Duc (2007): Sampling for vulnerability to poverty: Cost effectiveness versus precision. In: E. Tielkes: Tropentag 2007. Centre for International Rural Development, University of Kassel, Witzenhausen, Germany. Download

 

2011

Völker, Marc, Songporne Tongruksawattana, Hermann Waibel and Bernd Hardeweg (2011): Climate risk perception and ex-ante mitigation strategies of rural households in Thailand & Vietnam. Paper presented at 7. Jährliche Konferenz des Vereins für Socialpolitik, Research Committee Development Economics. June 24-25, Berlin, Germany. Download

Kislat, Carmen and Lukas Menkhoff (2011): The village fund loan: Who gets it, keeps it and loses it? Working Paper, presented at the 43rd Annual International Conference of the Money, Macro and Finance Research Group (MMF), September 15-17, Birmingham, UK. Download

Kemper, Niels, Rainer Klump and Heiner Schumacher (2011): Representation of property rights and credit market outcomes: Evidence from a land reform in Vietnam. Working Paper, presented at Verein für Socialpolitik, Frankfurt, Session: Credit and insurance in developing countries. (with Kristina Czura, Goethe University, and Ingo Outes, University of Oxford), 2011; Second European Research Conference on Microfinance, Groningen, Netherlands, 2011; Eighth Midwest International Economic Development Conference, University of Wisconsin-Madison, Madison, USA, 2011; and Verein für Socialpolitik (Entwicklungsländerausschuß), Berlin, 2011.

2010

Völker, Marc and Hermann Waibel (2010): Natural resource degradation as a response to shocks in mountainous areas of Vietnam. Paper presented at 6. Jährliche Konferenz des Vereins für Socialpolitik, Research Committee Development Economics. June 18-19, Hannover, Germany.

Völker, Marc, Songporne Tongruksawattana, Hermann Waibel and Erich Schmidt (2010): Incorporating vulnerability to poverty in farm level models: experiences from Thailand and Vietnam. Paper presented at 114. Seminar der European Association of Agricultural Economists (EAAE). April 15-16, Berlin, Germany.

Völker, Marc, Songporne Tongruksawattana, Hermann Waibel and Bernd Hardeweg (2010): Climate risk perception and ex-ante mitigation strategies of rural households in Thailand & Vietnam. Paper presented at 117. Seminar der European Association of Agricultural Economists (EAAE). November 25-27, Hohenheim, Germany. Download

Hohfeld, Lena (2010): Rural urban migration and agricultural investment. Poster presented at Tropentag 2010: World food system - A contribution from Europe. September 14-16, Zurich, Switzerland. Abstract

Hardeweg, Bernd, Lukas Menkhoff and Hermann Waibel (2010): Experimentally-validated survey evidence on individual risk attitudes in rural Thailand. Paper presented at 25th Annual Meeting of the European Economic Association, August 23-26, University of Glasgow, Scotland, and at Annual Conference of the Royal Economic Society, March 29-31, University of Surrey, Guildford, UK. Download

Hardeweg, Bernd, Andres Wagener and Hermann Waibel (2010): Towards comparative and aggregate vulnerability: Analysis of welfare distributions in rural rreas in Thailand and Viet Nam. Paper presented at Jahrestagung des Vereins für Socialpolitik. September 7-10, Kiel, Germany.

Gödecke, Theda and Hermann Waibel (2010): Is agriculture a good shock absorber for economic crisis? Empirical evidence from a rural village in Thailand. Paper presented at Tropentag 2010: World food system - A contribution from Europe. September 14-16, Zurich, Switzerland. Download

Gödecke, Theda and Hermann Waibel (2010): Shock mitigation and rural-urban migration during the recent Thai crisis. Paper presented at PEGNet Conference 2010: Policies to Foster and Sustain Equitable Development in Times of Crisis. September 2-3, Midrand, South Africa. Download

2009

Witt, Rudolf, Levison S. Chiwaula and Hermann Waibel (2009): Vulnerability and household livelihoods in small-scale fishing areas in Nigeria and Cameroon - An asset-based approach. Paper presented at Inaugural Conference of the Courant Research Centre 'Poverty, Equity and Growth'. July 1-3, Göttingen, Germany.

Waibel, Hermann (2009): Agriculture and economic crisis: "A South East Asian perspective". DAAD Stipendiatentreffen. June 20, Hannover, Germany. Download

Waibel, Hermann (2009): Collecting data to measure vulnerabilty to poverty: Some initial findings from Thailand and Vietnam. Seminar at the Faculty of the Economics and Rural Development, Hanoi University of Agriculture. September 30, Hanoi, Vietnam. Download

Waibel, Hermann (2009): Collecting data to measure vulnerabilty to poverty: Some initial findings from Thailand and Vietnam. Seminar at Thailand Development and Research Institute. September 25, Hue, Vietnam. Download

Völker, Marc, Erich Schmidt and Hermann Waibel (2009): Climatic risk and farm planning: A mathematical programming model for typical farms households in the mountainous upland of Thua Thien Hue Province, Vietnam. Paper presented at Tropentag 2009. October 6-8, Hamburg, Germany. Download

Völker, Marc (2009): The role of forest resource extraction as coping-mechanism for rural households in the mountainous upland of Thua Thien Hue province, Vietnam. Paper presented at Workshop of the DFG Research Group on Vulnerability to Poverty in Southeast-Asia. February 22-26, Hue, Vietnam.

Tongruksawattana, Songporne, Erich Schmidt and Hermann Waibel (2009): Shocks and coping strategies of agricultural households: First results from three provinces in Thailand. Paper presented at the Workshop of Research Unit 756 of the Deutsche Forschungsgemeinschaft (DFG). February 22-26, Hue City, Vietnam. Download

Tongruksawattana, Songporne, Erich Schmidt and Hermann Waibel (2009): Farm household adjustment to price shocks in Thailand. Paper presented at Tropentag 2009. October 6-8, Hamburg, Germany. Download

Praneetvatakul, Suwanna, Tung P. Duc and Hermann Waibel (2009): The role of shocks on the diversification of rural households: A comparison between Thailand and Vietnam. Paper presented at Tropentag 2009. October 6-8, Hamburg, Germany. Abstract

Menkhoff, Lukas and Ornsiri Rungruxsirivorn (2009): Village funds in the rural credit market of Thailand. Paper presented at the Workshop of Research Unit 756 of the Deutsche Forschungsgemeinschaft (DFG). February 22-26, Hue City, Vietnam. Download

Hardeweg, Bernd, Lukas Menkhoff and Hermann Waibel (2009): Experimentally-validated survey evidence on individual risk attitudes in rural Thailand. Poster presented at Tropentag 2009. October 6-8, Hamburg, Germany. www.tropentag.de , Download

Hardeweg, Bernd and Hermann Waibel (2009): The spatial distribution and interregional dynamics of vegetable production in Thailand. Poster presented at 49th Annual GEWISOLA Conference 2009. September 30 - October 2, Kiel, Germany.

Hardeweg, Bernd, Andres Wagener and Hermann Waibel (2009): Towards comparative and aggregate vulnerability: Analysis of welfare distributions in rural areas in Thailand and Viet Nam. Paper presented at Tropentag 2009. October 6-8, Hamburg, Germany. www.tropentag.de , Download

Hardeweg, Bernd and Hermann Waibel (2009): Collecting data to measure vulnerabilty to poverty: An overview. Paper presented at Workshop of the DFG Research Group "Impact of shocks on the vulnerability to poverty; consequences for development of Southeast Asian countries". February 22-26, Hue, Vietnam. Download

Hardeweg, Bernd, Lukas Menkhoff and Hermann Waibel (2009): Risk attitudes among the rural population of Ubon Ratchathani province, Thailand. Workshop of the DFG Research Group on Vulnerability to Poverty in Southeast-Asia. February 22-26, Hue, Vietnam.

Gödecke, Theda and Hermann Waibel (2009): The role of social support networks on household well-being: A village level case study in Northern Thailand. Paper presented at SUNBELT XXX - INSNA Conference. June 29 - July 4, Riva del Garda, Italy.

Gödecke, Theda and Hermann Waibel (2009): A village case study for vulnerability assessment: The implications of household definitions. Paper presented at Workshop of the DFG Research Group on Vulnerability to Poverty in Southeast-Asia, February 23-26, Hue, Vietnam, and at Arbeitskreis Südostasien in der deutschen Gesellschaft für Geographie. July 3-5, Köln, Germany.

Duc, Tung P. and Hermann Waibel (2009): Diversification in land and labor allocation in response to shocks among small-scale farmers in central Vietnam. Paper presented at 49th Annual GEWISOLA Conference 2009. September 30 - October 2, Kiel, Germany.

Chiwaula, Levison and Hermann Waibel (2009): The role of shocks and risks for the livelihoods of small scale fishing communities of Hadejia-Nguru Wetlands in Nigeria. Paper presented at Annual conference of Verein für Socialpolitik Ausschuss für Entwicklungsländer. 26-27 June 2009, Frankfurt.

2008

Witt, Rudolf, Diemuth E. Pemsl and Hermann Waibel (2008): Small-scale inland fisheries in Africa: How to collect data for poverty assessment? Paper presented at Annual Conference of "Verein für Socialpolitik: Research Committee Development Economics". May 30-31, Zürich. Download

Völker, Marc, Erich Schmidt and Hermann Waibel (2008): Approaches to modelling vulnerability to poverty in rural households in Thua Thien Hue province, Vietnam. Poster presented at Tropentag 2008. October 7-9, Hohenheim, Germany. Download

Tongruksawattana, Songporne, Erich Schmidt and Hermann Waibel (2008): Understanding vulnerability to poverty of rural agricultural households in Northeastern Thailand. Poster presented at Tropentag 2008. October 7-9, Hohenheim, Germany. Download

Hardeweg, Bernd and Hermann Waibel (2008): Income composition and perception of income fluctuation: Evidence from a representative household sample in three provinces of Thailand and Viet Nam. Poster presented at Tropentag 2008. October 7-9, Hohenheim, Germany. www.tropentag.de , Download

Chiwaula, Levison S. and Hermann Waibel (2008): Risks, shocks and their impact in small scale fishing communities of Hadejia-Nguru Wetlands in Nigeria. Paper presented at 6th European Development Research Network (EUDN) PhD Seminar. October 17-18, Göttingen, Germany.

2007

Hardeweg, Bernd, Suwanna Praneetvatakul, Tung P. Duc and Hermann Waibel (2007): Sampling for vulnerability to poverty: Cost effectiveness versus precision. Paper presented at Tropentag 2007. October 9-11, University of Kassel-Witzenhausen and University of Göttingen.

2006

Witt, Rudolf, Levison S. Chiwaula, Christophe Béné, Hermann Waibel and Diemuth E. Pemsl (2006): Methodology for economic valuation of food security and vulnerability to poverty for inland fisheries in Africa. Paper presented at Tropentag 2006. October 11-13, Bonn, Germany. Abstract