Browsing by Subject "Kautschukplantage"

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Developing a biodiversity evaluation tool and scenario design methods for the Greater Mekong Subregion
(2011) Cotter, Marc; Sauerborn, Joachim
The Xishuangbanna Prefecture in Yunnan Province (PR China) is facing increasing conflicts between rural development and nature conservation because of an ongoing expansion and commercialization of farming. The rapid development of large-scale farming and the improvement of infrastructure throughout the region are posing serious threats to the conservation of endemic species of flora and fauna, while also offering possibilities for enhancing the livelihood of rural populations to an extend never seen before. The expansion of rubber (Hevea brasiliensis Willd Ex A. Juss) has caused a reduction and fragmentation of natural and secondary forest cover, thereby decreasing structural and species diversity as well as the loss of valuable ecosystem services. The establishment of intensified agriculture, especially plantations on sloping terrain, often leads to an increased erosion risk, nutrient run-off and sedimentation in water courses. Thus, large scale deforestation is not just a problem for nature conservation but also one for the rural economies. Rural development and simultaneous environment conservation often face trade-offs, especially in regions that host an exceptionally high biodiversity, such as many tropical areas. In order to adequately consider and evaluate these interactions, tools and methods have to be developed that allow decision makers to assess the impacts of different management and infrastructure options on the environment. The aim of the work presented in this thesis was to analyze and evaluate the effect of large-scale rubber cultivation on local and regional biodiversity by developing methods to integrate field studies from various disciplines into a comprehensive assessment model. This model was then used to highlight key aspects of anthropogenic influence on the plant species composition within the research area and to identify possible impacts of alternative land use decisions. Furthermore, the development of an interdisciplinary approach to scientific scenario design methods has been supplemented with a study on the acceptance of 3D-visualization as communication tool for land use planning in the background of nature conservation sciences. In order to achieve this, an overview of the agronomical and ecological aspects of rubber cultivation was provided. Literature sources referring to the impact of different cultivation systems on natural biodiversity were discussed and an introduction to the effect of rubber cultivation on Ecosystem Services was given. A method for projection of regionally adapted carbon capture properties of rubber cultivation under suboptimal growth conditions was presented and a comparative assessment of greenhouse gas emissions during the establishment of rubber plantations in regard to the preexisting vegetation was made. A biodiversity evaluation tool based on the combination of approaches from landscape ecology and empirical data within a Geographic Information System was developed. Detailed data on plant species diversity and distribution were combined with quality criteria like endemism or invasiveness to form spatially explicit biodiversity indices for different land use types in various elevation classes. Up-scaling in accordance to the land use distribution observed allowed the estimation of overall plant diversity and the evaluation of the effect of possible future land use scenarios. Habitat characteristics and spatial distribution were included into the analysis of the land use map derived from remote sensing information to allow for the assessment of fragmentation and landscape matrix structure. The methodology was tested with an array of possible present and future land use maps. It was possible not only to evaluate the different land use classes within and their distribution throughout the research area, but we were also able to compare distinct sub-regions based on topography or administrative status. The challenges stakeholders and nature conservation face in the different elevation zones of Nabanhe were highlighted and related to the findings of our partner workgroups from economy and social sciences. The feasibility of this approach to administration staff with limited experience in ecological modeling was one of the main goals in designing the methods. Given a reasonable data set on species diversity and distribution within any given tropical research area, this approach will enable planners and nature park administration to quickly project possible consequences on species diversity indices deriving from land use change within their respective research area. Using this approach, the importance of natural tropical forests for the maintenance of species diversity in tropical cultivated landscapes was highlighted. With the information gained from constructing this evaluation tool, the design and development process for a land use scenario based on the integration of multidisciplinary assessments and iterative scenario refinement with repeated stakeholder inclusion was promoted. By combining stricter conservation rules with alternative sources of income for the rural population in order to offer an alternative to monoculture rubber farming, the economic models and the land use allocation model predicted a stop in rubber and agriculture related deforestation, and the establishment of a considerable amount of reforested area. This was achieved by introducing an innovative land use type that is closely related to traditional local home garden agroforestry systems. By coupling reforestation efforts with the economic gain derived from intercropping Traditional Chinese Medicinal plants into degraded secondary forests, this scenario was, at least theoretically, able to remove deforestation pressure from the natural forest types and to offer an economic alternative to rubber cultivation. The methods used for this assignment can serve as guideline for future projects that want to implement scenario design procedures based on the combination of social sciences, economics, ecology and landscape planning. The acceptance and comprehensibility of computer based 3D visualization models for the communication of possible future land use scenarios was also tested. Two alternative scenarios were visualized and compared to the status quo, with questionnaires and guided interviews covering the acceptability and adaptability of such techniques for professionals from various fields of nature conservation. This thesis presents an overview over agronomic, economic and ecological aspects of rubber cultivation and highlights its implications on biodiversity and nature conservation. The methods discussed here can serve as a guideline for the integration of ecological indicators in land use planning and decision making processes. Although the concepts and topics introduced herein are closely interlinked within the framework of the Living Landscapes China (LILAC) research project, the methods and approaches can easily be applied to other areas in the Greater Mekong Subregion and beyond, be it the expansion of oil palm plantations in the Malayan Archipelago or the fragmentation of forests due to increased population pressure in Central Africa. Nature conservation is facing similar problems all over the developing world, and adaptable approaches such as the ones presented here are needed to support decision making processes in order to secure the preservation and long-term survival of the worlds? diversity in species and natural habitats.
Impact of land use change on soil respiration and methane sink in tropical uplands, Southwestern China
(2020) Lang, Rong; Cadisch, Georg
Land use conversion could modulate soil CO2 emissions and the balance between CH4 oxidation and production via changing soil physical, chemical and biological properties. Large areas of natural forests have been converted to rubber plantations in Southeast Asia, but its impact on soil CO2 and CH4 fluxes has not been sufficiently understood. This study was conducted in Xishuangbanna, Southwestern China, aiming to quantify the impact of this land use change on soil CO2 and CH4 fluxes and to clarify mechanisms responsible for the differences between natural forests and rubber plantations. Dynamics of soil respiration rates in two land uses were compared, and a mixed effect model was used in studying the interference of soil moisture on estimating temperature sensitivity (Q10) of soil respiration (Chapter 2). The land use change impact on the ability of soils to function as CH4 sink was firstly assessed with surface CH4 fluxes measured by static chambers, and then assessed with gas concentration profiles determined from soil probes. Confounded controlling factors and land use effects were disentangled, and the pathway of interactions between CH4 processes and mineral nitrogen was identified (Chapter 3). The concentration gradient method and one-dimensional diffusion-oxidation model were applied to quantify the vertical distribution of CH4 uptake in soil profiles, and to separate the relative control by gas diffusivity and by methanotrophic oxidation on CH4 uptake (Chapter 4). Distinct different temporal patterns of soil respiration were observed on sites during most of the rainy season: forest maintained a high soil respiration rate, while soil respiration in rubber plantations became suppressed (by up to 69%). Forest soils thus emitted the highest amount of CO2 with an annual cumulative flux of 8.48 ± 0.71 Mg C ha-1 yr-1, compared to 6.75 ± 0.79, 5.98 ± 0.42 and 5.09 ± 0.47 Mg C ha-1 yr-1 for 22-year-old rubber, rubber-tea intercropping, and 9-year-old rubber, respectively. Adding a quadratic soil moisture term into the regression model accounted for interference of moisture effect on the effect by soil temperature, therefore, improved temperature sensitivity assessments when high soil moisture suppressed soil respiration under rubber plantations. The static chamber method showed that soils under natural forest were stronger CH4 sinks than soils under rubber plantations, with annual CH4 fluxes of -2.41 ± 0.28 kg C ha-1 yr-1 and -1.01 ± 0.23 kg C ha-1 yr-1, respectively. Water-filled pore space was the main factor explaining the differences between natural forests and rubber plantations. Although soils under rubber plantations were more clayey than soils under natural forest, this was proved not to be the decisive factor driving higher soil moisture and lower CH4 uptake in the former soils. Concentration gradients method showed that CH4 consumption in 0-5 cm soil was significantly higher in natural forests than in rubber plantations, with a mean CH4 flux of -23.8 ± 1.0 and -14.4 ± 1.0 ug C m-2 h-1 for forest and rubber plantations, respectively. The atmospheric CH4 oxidized by top 10 cm soil accounted for 93% and 99% of total consumption for forest and rubber plantations, respectively. CH4 diffusivity at four sampled depths were significantly lower in rubber plantation than in forest. This reduced CH4 diffusivity, caused by altered soil water regime, predominately explained the weakened CH4 sink in converted rubber plantations. Estimated isotopic fractionation factor for carbon due to CH4 oxidation was 1.0292 ± 0.0015 (n=12). Modeling 13CH4 distribution in soil profiles using a diffusion-oxidation model explained the observations in the dry season, but suggested CH4 production in subsoil in the rainy season. In summary, converting natural forests into rubber plantations tended to reduce soil CO2 emissions, but this conversion substantially weakened CH4 uptake by tropical upland soils. The altered soil water regime and conditions of soil aeration under converted rubber plantations appear to have a pronounced impact on processes of gaseous carbon fluxes from soils. The clarified mechanisms in this study could improve the regional budget of greenhouse gases emissions in response to land use change and climate change.