Zahlungen für Ökosystemdienstleistungen (Payments for EcosystemServices, PES) sind in den letzten Jahren zum Aushängeschild von Umweltorganisation geworden. Der Gedanke, die Bereitstellung von Ökosystemdienstleistungen durch PES abzusichern, ist in praktischen Diskursen von Vermittlern zu finden, die an potentiell Zahlende gerichtet sind. Praktikern ist bisher jedoch schwer gefallen, zu zeigen, dass PES tatsächlich zu den vorgesehenen Zielen führen können. Forscher haben darauf hingewiesen, dass zahlreiche PES-Schemata, insbesondere diejenigen mit Bezug auf Wasser, auf unsicheren Annahmen beruhen und außerdem gewichtige Kausalzusammenhänge zwischen Eingriffen in die Landnutzung und Ökosystemdienstleistungen vermissen lassen. Diese Unsicherheit in PES-Schemata geht nicht nur aus praktischen Schwierigkeiten hervor, sondern aus der Komplexität von Mensch-Umwelt-Systemen (human-environment systems) und aus der Begrenztheit des Wissens über diese Systeme. Forscher sind zwar in derLage, diese wesentlichen Herausforderungen zu beschreiben und zu diskutieren. In der Fachliteratur mangelt es jedoch an empirischen Studien,die die zusätzliche Wirksamkeitvon PES-Schemata untersuchen, d.h. ob diese Schemata zusätzliche Wirkungen zeigen, die anderen Faktoren nicht zurechenbar sind, bzw. Studien, die die Bedeutung von Nachweisen für ihre Wirksamkeit für die Interessengruppen (stakeholders) untersuchen. Die Dissertation trägt dazu bei, diese empirische Lücke zu schließen: Dazu untersucht sie vier wasserbezogene Zahlungsschemata, hier auch Zahlungen für Wassereinzugsgebietsleistungen genannt, in Kolumbien. Sie vergleicht die vier Fälle hinsichtlich der Bestrebungen, durch Beobachtung (monitoring) und Evaluation Nachweise für die Wirksamkeit zu erbringen, sowie hinsichtlich der damit verbundenen Herausforderungen. Eines der Kapitel enthält auch drei Fallstudien aus Brasilien, die als Vergleich zu den Fällen aus Kolumbien und der Darstellung von Unterschieden und Gemeinsamkeiten dienen. / Payments for Ecosystem Services (PES) have become the flagship of conservation organizations in recent years. The idea of securing ecosystem service (ES) provision through PES has been present in practical discourses of intermediaries directed at potential payers. However, demonstrating that PES can actually achieve the intended goals has been difficult for practitioners. Researchers have pointed out that many PES schemes, particularly water-related ones, are based on unreliable assumptions and lack strong causal links between land use interventions and ecosystem services. This uncertainty in PES schemes arises not only from practical difficulties, but from the complexity of human-environment systems (HES), and the limits of knowledge about them. Researchers have been able to describe and discuss these major challenges. However, the literature is still poor on empirical studies exploring the additionality of PES schemes, that is, if those schemes produce additional effects not attributable to other factors, as well as studies exploring the importance of impact evidence for stakeholders involved. This dissertation contributes to filling this empirical gap by exploring four water-related payments schemes (here also called payments for watershed services, PWS) in Colombia, comparing the cases in terms of their efforts to produce impact evidence through monitoring and evaluation, and their associated challenges. Three cases from Brazil are also included in one of the chapters and compared with the Colombian cases by illustrating differences and similarities.

On the frontier of biodiversity-rich tropical forests, how land is used has an important role in buffering the primary ecosystem. Unsustainable small-scale cattle farming endangers soil quality and degrades the landscape. Silvopasture is a type of agroforestry that provides both ecological and livelihood benefits. A number of projects have been implemented across the tropics to encourage silvopasture adoption, with varying success. This dissertation questions the reasons for variable outcomes among participants within these projects: what motivates smallholders to adopt innovative land-use practices, and what form of incentives may help to overcome obstacles and catalyse adoption. This dissertation contributes to the ongoing debate on payments for ecosystem services, specifically about their suitability and effectiveness. To understand what influences decisions to adopt sustainable land-use practices, I review systematically and quantitatively the literature on adoption predictors, and I empirically analyse participation and short-term adoption in a pilot project for planting fodder trees in the border of a protected forest in Chiapas, Mexico, using primary and secondary data. I focus on subjective perspectives and livelihood strategies of actual and potential participants as explanatory variables, which have received unduly scarce attention in past studies. This lack of attention is partially caused by the difficulties of operationalising internal variables. I address this challenge by developing an analytical approach that increases the precision of the resulting perspectives in Q methodology. I cluster livelihood strategies and model adoption. This in-depth case-study suggests the type of incentives that are adequate to encourage adoption of sustainable land-use practices. Results indicate that payments may not be the best incentive for pioneer adopters, and that the adoption process is composed of separate individual steps, which are influenced distinctly by identifiable predictors, such as livelihood diversity. Uncovering this heterogeneity of motivations towards adoption provides useful knowledge for designing more effective external policy interventions.