Simulating the impact of land use change and climate change on the supply of ecosystem services in a rubber-dominated watershed in Southwestern China

This cumulative PhD thesis investigates the expansion of rubber (Hevea brasiliensis Müll. Arg.) plantations and the ensuing multiple impacts on biodiversity and the supply of ecosystem services (ESS) in a mountainous watershed in Xishuangbanna Prefecture, Southwestern China. In recent decades, the study area, the Nabanhe Reserve, saw the expansion of rubber plantations and the loss of extensive forest areas, which led to a substantial decline in ESS. Workshops with regional stakeholders resulted in the development of three future land use scenarios for Nabanhe Reserve (2015 2040), varying in their degree of rubber expansions, management options and reforestations efforts. In the first study, the InVEST (Integrated Valuation of Ecosystem Services and Trade-offs) modeling framework was used to analyze the impact of these rubber expansion scenarios on selected ESS: sediment retention, water yield, habitat quality, and carbon sequestration. In addition, a model for assessing potential rubber yields was developed and implemented in ArcGIS. The analysis also included different statistical weighting methods to include rankings for the preference of ESS from three contrasting stakeholder groups (prefecture administration, tourists, off-site citizens). The study concludes that the integrated ESS indices would be overestimated without the inclusion of the stakeholder groups. The second study introduced a new method to identify potential tipping points in the supply of ESS. Here, time-series data derived from InVEST have been combined with a sequential, data-driven algorithm (R-method) to identify potential tipping points in the supply of ESS within two contrasting scenarios of rubber expansion in Nabanhe Reserve. The tipping point analysis included hydrological, agronomical, and climate-regulation ESS, as well as multiple facets of biodiversity. The model results showed regime shifts indicating potential tipping points, which were linked to abrupt changes in rubber yields, in both scenarios and at varying spatial scales. The study concludes that sophisticated land use planning may provide benefits in the supply of ESS at watershed scale, but that potential trade-offs at sub-watershed scales should not be neglected. The third study focused on modeling hydrological ESS (water yield and sediment export) in Nabanhe Reserve under multiple scenarios of land use and climate change in order to assess how both drivers influence the supply of these ESS. Three rubber expansion scenarios were analyzed in combination with multiple climate change scenarios using the InVEST modeling framework. Simulation results showed that the effect of land use and land management decisions on water yield in Nabanhe Reserve are relatively minor (4% difference in water yield between land use scenarios), when compared to the effects that future climate change will exert on water yield (up to 15% increase or 13% decrease in water yield compared to the baseline climate). Changes in sediment export were more sensitive to land use change (15% increase or 64% decrease) in comparison to the effects of climate change (up to 10% increase). The study concludes that in the future, particularly dry years may have a more pronounced effect on the water balance in Nabanhe Reserve as the higher potential evapotranspiration increases the probability for periods of water scarcity, especially in the dry season. In conclusion, the studies showed detrimental consequences induced by rubber expansions for all assessed ESS, with the exception of rubber yields. Further continuing the trend of rubber expansions in the study area is not the best option in terms of integrated ESS supply on a landscape scale. Land use planning alternatives, such as rubber expansions restricted to suitable areas only, in combination with reforestation efforts at less suitable locations, may be used to keep crucial environmental functions intact. Policy regulations at the local level, if properly assessed with spatial models and integrated stakeholder feedback, have the potential to buffer the typical trade-off between agricultural intensification and environmental protection. The implementation of these regulations might still pose a considerable challenge. The methods introduced in this Dissertation can easily be transferred to regions facing comparable land use situations, as InVEST and a large amount of the utilized spatial datasets are freely available.Die vorgelegte Doktorarbeit befasst sich mit der Ausweitung von Kautschukplantagen (Hevea brasiliensis Müll. Arg.) und den daraus folgenden vielfältigen Auswirkungen auf Biodiversität und die Bereitstellung von Ökosystemdienstleistungen (ÖSD) in einem bergigen Wassereinzugsgebiet in der Präfektur Xishuangbanna im Südwesten Chinas. In den vergangenen Jahrzehnten kam es im Untersuchungsgebiet, dem Nabanhe-Reservat, zu einer rasanten Ausweitung von Kautschukplantagen und dem Verlust weitläufiger Waldflächen und Ökosystemdienstleistungen. Aus Workshops mit regionalen Interessenvertretern entstanden drei Landnutzungsszenarien für die Zukunft des Nabanhe-Reservats (2015 2040), die sich hinsichtlich des Ausmaßes der Kautschukausweitung, verschiedener Managementoptionen und Wiederaufforstungsstrategien unterscheiden. In der ersten Fallstudie wurde das Model InVEST (Integrated Valuation of Ecosystem Services and Trade-Offs) verwendet, um die Auswirkungen der Landnutzungsszenarien auf vier ausgewählte ÖSD zu analysieren: Sedimentretention, Wasserertrag, Habitat-Qualität und Kohlenstoffbindung. Zusätzlich wurde ein Modell zur Abschätzung potenzieller Kautschukerträge entwickelt und in ArcGIS implementiert. Weiterhin wurden verschiedene statistische Gewichtungsmethoden benutzt, um die Präferenzen dreier kontrastierender Interessengruppen (Präfektur-Administration, Touristen, Externe Bürger) in der Auswertung der ÖSD Ergebnisse miteinzubinden. Die Studie kommt zu dem Schluss, dass die integrierten ÖSD Indizes ohne die Einbeziehung der Interessengruppen überbewertet würden. Die zweite Studie stellt eine neue Methode zur Identifikation potenzieller Kipp-Punkte (KP) in der Bereitstellung von ÖSD vor. Hierbei werden Zeitreihendaten von InVEST mit einem sequenziellen, datengetriebenen Algorithmus (R-Methode) kombiniert, um potenzielle KP in der Bereitstellung von ÖSD innerhalb zweier gegensätzlicher Landnutzungsszenarios abzuleiten. Die KP-Analyse umfasste hydrologische, agronomische und klimaregulierende ÖSD sowie mehrere Facetten der Artenvielfalt. Die Modellergebnisse zeigten in beiden Landnutzungsszenarien auf unterschiedlichen räumlichen Skalen Regimeverschiebungen, die auf potenzielle KP hindeuteten und aus abrupten Veränderungen der Kautschukerträge hervorgingen. Verbesserungen in der Bereitstellung von ÖSD können mit Hilfe von gut geplanten Landnutzungsstrategien auf der Skalenebene von Wassereinzugsgebieten erreicht werden. Potenzielle Trade-Offs auf kleineren Skalenebenen sollten jedoch auch beachtet werden. Die dritte Studie befasste sich mit der Modellierung hydrologischer ÖSD (Wasserertrag und Sedimentretention) im Nabanhe-Reservat unter verschiedenen Landnutzungs- und Klimawandelszenarien, um zu beurteilen, wie beide Faktoren die Bereitstellung dieser ÖSD beeinflussen. Drei Landnutzungsszenarien wurden in Kombination mit mehreren Klimawandel-Szenarien mit Hilfe von InVEST analysiert. Die Simulationsergebnisse zeigen, dass die Auswirkungen von Landnutzungs- und Landmanagemententscheidungen auf den Wasserertrag im Nabanhe-Reservat relativ gering sind (ein Unterschied von 4% im Wasserertrag zwischen den Landnutzungsszenarien), insbesondere wenn man sie mit den Auswirkungen des bevorstehenden Klimawandels vergleicht (eine 15% Zunahme oder 13% Abnahme des Wasserertrags verglichen mit dem Baseline-Klima). Sedimentexportwerte reagierten sensitiver auf Landnutzungsänderungen (15% Zunahme oder 64% Abnahme) im Vergleich zu den Auswirkungen des Klimawandels (bis zu 10% Zunahme). Die Studie kommt zu dem Schluss, dass sich in Zukunft besonders trockene Jahre stärker auf den Wasserhaushalt im Nabanhe-Reservat auswirken könnten, da die höhere potenzielle Evapotranspiration die Wahrscheinlichkeit für Zeiten der Wasserknappheit erhört, was insbesondere in der Trockenzeit eintreten könnte. Zusammenfassend zeigten die Studien nachteilige Folgen der Kautschukausweitung in Bezug auf alle betrachteten ÖSD mit Ausnahme der Kautschukerträge. Auf Landschaftsebene ist die zusätzliche Ausweitung von Kautschukflächen nicht die beste Option im Hinblick auf die integrierte ÖSD Bereitstellung. Alternativen der Landnutzungsplanung, wie z.B. die Kautschukausweitung auf geeignete Flächen zu beschränken und andere Flächen wieder aufzuforsten, können genutzt werden, um wichtige Umweltfunktionen zu erhalten. Politische Regelungen auf lokaler Ebene haben das Potenzial den typischen Zielkonflikt zwischen landwirtschaftlicher Intensivierung und Umweltschutz zu mildern, sofern sie mit räumlich expliziter Modellierung und dem Feedback von Interessengruppen ausgewertet werden. Die Umsetzung solcher Regelungen könnte jedoch eine beträchtliche Herausforderung darstellen. Die in dieser Dissertation vorgestellten Methoden können leicht auf Regionen mit vergleichbaren Landnutzungssituationen übertragen werden, da sowohl InVEST als auch der Großteil der verwendeten räumlichen Datensätze frei verfügbar sind

Tipping Points in the Supply of Ecosystem Services of a Mountainous Watershed in Southeast Asia

This resesarch article published by MDPI, 2018Rubber plantations have expanded at an unprecedented rate in Southeast Asia in recent decades. This has led to a substantial decline in the supply of ecosystem services (ESS) and has reduced livelihood options and socioeconomic well-being in rural areas. We assessed the impact of two land use scenarios on the supply of ESS in a mountainous watershed in Xishuangbanna Prefecture, People’s Republic of China. We combined time-series data derived from spatially explicit ESS models (InVEST) with a sequential, data-driven algorithm (R-method) to identify potential tipping points (TPs) in the supply of ESS under two rubber plantation expansion scenarios. TPs were defined as any situation in which the state of a system is changed through positive feedback as a result of accelerating changes. The TP analysis included hydrological, agronomical, and climate-regulation ESS, as well as multiple facets of biodiversity (habitat quality for vertebrate, invertebrate, and plant species). We identified regime shifts indicating potential tipping points, which were linked to abrupt changes in rubber yields, in both scenarios at varying spatial scales. With this study, we provide an easily applicable method for regional policy making and land use planning in data-scarce environments to reduce the risk of traversing future TPs in ESS supply for rubber producing land use systems

Using agent-based modelling to simulate social-ecological systems across scales

Agent-based modelling (ABM) simulates Social-Ecological-Systems (SESs) based on the decision-making and actions of individual actors or actor groups, their interactions with each other, and with ecosystems. Many ABM studies have focused at the scale of villages, rural landscapes, towns or cities. When considering a geographical, spatially-explicit domain, current ABM architecture is generally not easily translatable to a regional or global context, nor does it acknowledge SESs interactions across scales sufficiently; the model extent is usually determined by pragmatic considerations, which may well cut across dynamical boundaries. With a few exceptions, the internal structure of governments is not included when representing them as agents. This is partly due to the lack of theory about how to represent such as actors, and because they are not static over the time-scales typical for social changes to have significant effects. Moreover, the relevant scale of analysis is often not known a priori, being dynamically determined, and may itself vary with time and circumstances. There is a need for ABM to cross the gap between micro-scale actors and larger-scale environmental, infrastructural and political systems in a way that allows realistic spatial and temporal phenomena to emerge; this is vital for models to be useful for policy analysis in an era when global crises can be triggered by small numbers of micro-level actors. We aim with this thought-piece to suggest conceptual avenues for implementing ABM to simulate SESs across scales, and for using big data from social surveys, remote sensing or other sources for this purpose

Assessing Ecosystem Services in Rubber Dominated Landscapes in South-East Asia—A Challenge for Biophysical Modeling and Transdisciplinary Valuation

The concept of ecosystem services (ESS) has been increasingly recognized for its potential in decision making processes concerning environmental policy. Multidisciplinary projects on rubber (Hevea brasiliensis) cultivation, integrating research on a variety of ESS, have been few and far between. More than three years of iterative workshops with regional stakeholders resulted in the development of future land use scenarios for our study area in Xishuangbanna, PR China. We used the InVEST (Integrated Valuation of Ecosystem Services and Trade-offs) modeling framework to analyze their impact on sediment retention, water yield, habitat quality, and carbon sequestration and developed a model for assessing rubber yields. We investigated the percentage deviations of integrated ESS indices in each scenario, as compared to the initial state of 2015 and as a novelty used different statistical weighting methods to include rankings for the preference of ESS from three contrasting stakeholder groups. The business-as-usual scenario (BAU, continuous rubber expansions) revealed an increase in rubber yields trading off against all other ESS analyzed. Compared to BAU, the measures introduced in the balanced-trade-offs scenario (reforestation, reduced herbicide application, riverine buffer zones, etc.) reduced the total amount of rubber yield but enhanced habitat quality and regulating ESS. The results show that the integrated indices for the provisioning of ESS would be overestimated without the inclusion of the stakeholder groups. We conclude that policy regulations, if properly assessed with spatial models and integrated stakeholder feedback, have the potential to buffer the typical trade-off between agricultural intensification and environmental protection.Peer Reviewe

Assessing Hydrological Ecosystem Services in a Rubber-Dominated Watershed under Scenarios of Land Use and Climate Change

Land use and climate change exert pressure on ecosystems and threaten the sustainable supply of ecosystem services (ESS). In Southeast-Asia, the shift from swidden farming to permanent cash crop systems has led to a wide range of impacts on ESS. Our study area, the Nabanhe Reserve in Yunnan province (PR China), saw the loss of extensive forest areas and the expansion of rubber (Hevea brasiliensis Müll. Arg.) plantations. In this study, we model water yield and sediment export for a rubber-dominated watershed under multiple scenarios of land use and climate change in order to assess how both drivers influence the supply of these ESS. For this we use three stakeholder-validated land use scenarios, varying in their degree of rubber expansion and land management rules. As projected climate change varies remarkably between different climate models, we combined the land use scenarios with datasets of temperature and precipitation changes, derived from nine General Circulation Models (GCMs) of the Fifth Assessment Report of the IPCC (Intergovernmental Panel on Climate Change) in order to model water yield and sediment export with InVEST (Integrated Valuation of Ecosystem Services and Trade-offs). Simulation results show that the effect of land use and land management decisions on water yield in Nabanhe Reserve are relatively minor (4% difference in water yield between land use scenarios), when compared to the effects that future climate change will exert on water yield (up to 15% increase or 13% decrease in water yield compared to the baseline climate). Changes in sediment export were more sensitive to land use change (15% increase or 64% decrease) in comparison to the effects of climate change (up to 10% increase). We conclude that in the future, particularly dry years may have a more pronounced effect on the water balance as the higher potential evapotranspiration increases the probability for periods of water scarcity, especially in the dry season. The method we applied can easily be transferred to regions facing comparable land use situations, as InVEST and the IPCC data are freely available