@phdthesis{Schollaen2014,
  author    = {Schollaen, Karina},
  title     = {Tracking climate signals in tropical trees},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus-71947},
  school      = {Universit{\"a}t Potsdam},
  year      = {2014},
  abstract  = {The tropical warm pool waters surrounding Indonesia are one of the equatorial heat and moisture sources that are considered as a driving force of the global climate system. The climate in Indonesia is dominated by the equatorial monsoon system, and has been linked to El Ni{\~n}o-Southern Oscillation (ENSO) events, which often result in severe droughts or floods over Indonesia with profound societal and economic impacts on the populations living in the world's fourth most populated country. The latest IPCC report states that ENSO will remain the dominant mode in the tropical Pacific with global effects in the 21st century and ENSO-related precipitation extremes will intensify. However, no common agreement exists among climate simulation models for projected change in ENSO and the Australian-Indonesian Monsoon. Exploring high-resolution palaeoclimate archives, like tree rings or varved lake sediments, provide insights into the natural climate variability of the past, and thus helps improving and validating simulations of future climate changes. Centennial tree-ring stable isotope records | Within this doctoral thesis the main goal was to explore the potential of tropical tree rings to record climate signals and to use them as palaeoclimate proxies. In detail, stable carbon (δ13C) and oxygen (δ18O) isotopes were extracted from teak trees in order to establish the first well-replicated centennial (AD 1900-2007) stable isotope records for Java, Indonesia. Furthermore, different climatic variables were tested whether they show significant correlation with tree-ring proxies (ring-width, δ13C, δ18O). Moreover, highly resolved intra-annual oxygen isotope data were established to assess the transfer of the seasonal precipitation signal into the tree rings. Finally, the established oxygen isotope record was used to reveal possible correlations with ENSO events. Methodological achievements | A second goal of this thesis was to assess the applicability of novel techniques which facilitate and optimize high-resolution and high-throughput stable isotope analysis of tree rings. Two different UV-laser-based microscopic dissection systems were evaluated as a novel sampling tool for high-resolution stable isotope analysis. Furthermore, an improved procedure of tree-ring dissection from thin cellulose laths for stable isotope analysis was designed. The most important findings of this thesis are: I) The herein presented novel sampling techniques improve stable isotope analyses for tree-ring studies in terms of precision, efficiency and quality. The UV-laser-based microdissection serve as a valuable tool for sampling plant tissue at ultrahigh-resolution and for unprecedented precision. II) A guideline for a modified method of cellulose extraction from wholewood cross-sections and subsequent tree-ring dissection was established. The novel technique optimizes the stable isotope analysis process in two ways: faster and high-throughput cellulose extraction and precise tree-ring separation at annual to high-resolution scale. III) The centennial tree-ring stable isotope records reveal significant correlation with regional precipitation. High-resolution stable oxygen values, furthermore, allow distinguishing between dry and rainy season rainfall. IV) The δ18O record reveals significant correlation with different ENSO flavors and demonstrates the importance of considering ENSO flavors when interpreting palaeoclimatic data in the tropics. The findings of my dissertation show that seasonally resolved δ18O records from Indonesian teak trees are a valuable proxy for multi-centennial reconstructions of regional precipitation variability (monsoon signals) and large-scale ocean-atmosphere phenomena (ENSO) for the Indo-Pacific region. Furthermore, the novel methodological achievements offer many unexplored avenues for multidisciplinary research in high-resolution palaeoclimatology.},
  language  = {en}
}
@phdthesis{Hassler2013,
  author    = {Haßler, Sibylle Kathrin},
  title     = {Saturated hydraulic conductivity in the humid tropics : sources of variability, implications for monitoring and effects on near-surface hydrological flow paths},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus-66864},
  school      = {Universit{\"a}t Potsdam},
  year      = {2013},
  abstract  = {Large areas in the humid tropics are currently undergoing land-use change. The decrease of tropical rainforest, which is felled for land clearing and timber production, is countered by increasing areas of tree plantations and secondary forests. These changes are known to affect the regional water cycle as a result of plant-specific water demand and by influencing key soil properties which determine hydrological flow paths. One of these key properties sensitive to land-use change is the saturated hydraulic conductivity (Ks) as it governs vertical percolation of water within the soil profile. Low values of Ks in a certain soil depth can form an impeding layer and lead to perched water tables and the development of predominantly lateral flow paths such as overland flow. These processes can induce nutrient redistribution, erosion and soil degradation and thus affect ecosystem services and human livelihoods. Due to its sensitivity to land-use change, Ks is commonly used to assess the associated changes in hydrological flow paths. The objective of this dissertation was to assess the effect of land-use change on hydrological flow paths by analysing Ks as indicator variable. Sources of Ks variability, their implications for Ks monitoring and the relationship between Ks and near-surface hydrological flow paths in the context of land-use change were studied. The research area was located in central Panama, a country widely experiencing the abovementioned changes in land use. Ks is dependent on both static, soil-inherent properties such as particle size and clay mineralogy and dynamic, land use-dependent properties such as organic carbon content. By conducting a pair of studies with one of these influences held constant in each, the importance of static and dynamic properties for Ks was assessed. Applying a space-for-time approach to sample Ks under secondary forests of different age classes on comparable soils, a recovery of Ks from the former pasture use was shown to require more than eight years. The process was limited to the 0-6 cm sampling depth and showed large variability among replicates. A wavelet analysis of a Ks transect crossing different soil map units under comparable land cover, old-growth tropical rainforest, showed large small-scale variability, which was attributed to biotic influences, as well as a possible but non-conclusive influence of soil types. The two results highlight the importance of dynamic, land use-dependent influences on Ks. Monitoring studies can help to quantify land use-induced change of Ks, but there is a variety of sampling designs which differ in efficiency of estimating mean Ks. A comparative study of four designs and their suitability for Ks monitoring is used to give recommendations about designing a Ks monitoring scheme. Quantifying changes in spatial means of Ks for small catchments with a rotational stratified sampling design did not prove to be more efficient than Simple Random Sampling. The lack of large-scale spatial structure prevented benefits of stratification, and large small-scale variability resulting from local biotic processes and artificial effects of destructive sampling caused a lack of temporal consistency in the re-sampling of locations, which is part of the rotational design. The relationship between Ks and near-surface hydrological flow paths is of critical importance when assessing the consequences of land-use change in the humid tropics. The last part of this dissertation aimed at disclosing spatial relationships between Ks and overland flow as influenced by different land cover types. The effects of Ks on overland-flow generation were spatially variable, different between planar plots and incised flowlines and strongly influenced by land-cover characteristics. A simple comparison of Ks values and rainfall intensities was insufficient to describe the observed pattern of overland flow. Likewise, event flow in the stream was apparently not directly related to overland flow response patterns within the catchments. The study emphasises the importance of combining pedological, hydrological, meteorological and botanical measurements to comprehensively understand the land use-driven change in hydrological flow paths. In summary, Ks proved to be a suitable parameter for assessing the influence of land-use change on soils and hydrological processes. The results illustrated the importance of land cover and spatial variability of Ks for decisions on sampling designs and for interpreting overland-flow generation. As relationships between Ks and overland flow were shown to be complex and dependent on land cover, an interdisciplinary approach is required to comprehensively understand the effects of land-use change on soils and near-surface hydrological flow paths in the humid tropics.},
  language  = {en}
}
@article{Ette2011,
  author    = {Ette, Ottmar},
  title     = {Alexander von Humboldt: Wissenschaft im Feld},
  series = {Alexander von Humboldt im Netz ; international review for Humboldtian studies},
  volume    = {XII},
  journal   = {Alexander von Humboldt im Netz ; international review for Humboldtian studies},
  number    = {23},
  publisher = {Universit{\"a}tsverlag Potsdam},
  address   = {Potsdam},
  issn      = {2568-3543},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus-57553},
  pages     = {9 -- 25},
  year      = {2011},
  abstract  = {Alexander von Humboldt verstand sich zwar sicher nicht als Direktor eines Museums, war aber sehr wohl der Welt der Museen, Bibliotheken und Archive nicht nur als Besucher und Leser, sondern auch als Sammler und Forscher verpflichtet. Durch seine Forschungsreisen nach Amerika und Asien vermehrte er im Verlauf eines langen Gelehrtenlebens viele Sammlungen durch eigene Sammelt{\"a}tigkeit vor Ort. Seine Feldforschung blieb dabei nicht auf naturwissenschaftliche Aspekte begrenzt, sondern bezog ganz selbstverst{\"a}ndlich auch die verschiedenartigsten kulturwissenschaftlichen Forschungsgegenst{\"a}nde mitein. Diese transdisziplin{\"a}r agierende Praxis im Feld l{\"a}sst sich zugleich als eine transareale, einzelne Areas {\"u}bergreifende und damit im Sinne von TransArea Studies aus den Beziehungen, Zirkulationen und Wechselwirkungen jenseits des bloß Territorialen sich speisende Wissenschaftskonzeption begreifen. So l{\"a}sst sich in seiner Auseinandersetzung mit der amerikanischen Tropenwelt eine doppelte transareale Relationalit{\"a}t erkennen, die einerseits intern die Tropenwelt unterschiedlicher Kontinente miteinander verbindet, andererseits aber extern die Tropen insbesondere mit den gem{\"a}ßigten Zonen in Relation setzt, um dadurch erst globale Zusammenh{\"a}nge - einschließlich der sich ver{\"a}ndernden Schneegrenzen oder der Wanderungsbewegungen der Pflanzenformen, f{\"u}r die sich die mobile Wissenschaft Humboldts in besonderem Maße interessierte - skizzieren und erl{\"a}utern zu k{\"o}nnen. Die Tropen sind f{\"u}r ihn die Zone h{\"o}chster Mannigfaltigkeit und Vielverbundenheit - oder um es mit heutigen Begriffen zum Ausdruck zu bringen: die TransArea par excellence.},
  language  = {de}
}
@misc{KnoblochSchwarzEtteetal.2011,
  author    = {Knobloch, Eberhard and Schwarz, Ingo and Ette, Ottmar and P{\´e}aud, Laura and Reich, Karin and Biermann, Kurt-Reinhard},
  title     = {HiN : Alexander von Humboldt im Netz},
  volume    = {XII},
  number    = {23},
  editor    = {Ette, Ottmar and Knobloch, Eberhard},
  publisher = {Universit{\"a}tsverlag Potsdam},
  address   = {Potsdam},
  issn      = {1617-5239},
  doi       = {10.18443/hinvol12iss232011},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus-57517},
  pages     = {73},
  year      = {2011},
  abstract  = {Inhalt: - Eberhard Knobloch/Ingo Schwarz: Die Feuer von Baku - ein wiederentdeckter Brief von Alexander von Humboldt - Ottmar Ette: Alexander von Humboldt: Wissenschaft im Feld - Transareale Wissenschaftsfelder in den Tropen - Laura P{\´e}aud: Le politique, op{\´e}rateur de la construction des savoirs g{\´e}ographiques modernes: l'exemple des voyages d'Alexander von Humboldt - Karin Reich: Sternschnuppen und Erdmagnetismus, ein von Alexander von Humboldt und Carl Friedrich Gauß w{\"a}hrend der Universit{\"a}tsfeierlichkeiten in G{\"o}ttingen im September 1837 initiiertes Projekt - Kurt-R. Biermann: War Alexander von Humboldt ein „Freiherr" (oder „Baron")?},
  language  = {mul}
}
@phdthesis{Zimmermann2007,
  author    = {Zimmermann, Beate},
  title     = {Spatial and temporal variability of the soil saturated hydraulic conductivity in gradients of disturbance},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus-16402},
  school      = {Universit{\"a}t Potsdam},
  year      = {2007},
  abstract  = {As land-cover conversion continues to expand into ever more remote areas in the humid tropics, montane rainforests are increasingly threatened. In the south Ecuadorian Andes, they are not only subject to man-made disturbances but also to naturally occurring landslides. I was interested in the impact of this ecosystem dynamics on a key parameter of the hydrologic cycle, the soil saturated hydraulic conductivity (synonym: permeability; Ks from here on), because it is a sensitive indicator for soil disturbances. My general objective was to quantify the effects of the regional natural and human disturbances on the saturated hydraulic conductivity and to describe the resulting spatial-temporal patterns. The main hypotheses were: 1) disturbances cause an apparent displacement of the less permeable soil layer towards the surface, either due to a loss of the permeable surface soil after land-sliding, or as a consequence of the surface soil compaction under cattle pastures; 2) 'recovery' from disturbance, either because of landslide re-vegetation or because of secondary succession after pasture abandonment, involves an apparent displacement of the less permeable layer back towards the original depth an 3) disturbances cause a simplification of the Ks spatial structure, i.e. the spatially dependent random variation diminishes; the subsequent recovery entails the re-establishment of the original structure. In my first study, I developed a synthesis of recent geostatistical research regarding its applicability to soil hydraulic data, including exploratory data analysis and variogram estimation techniques; I subsequently evaluated the results in terms of spatial prediction uncertainty. Concerning the exploratory data analysis, my main results were: 1) Gaussian uni- and bivariate distributions of the log-transformed data; 2) the existence of significant local trends; 3) no need for robust estimation; 4) no anisotropic variation. I found partly considerable differences in covariance parameters resulting from different variogram estimation techniques, which, in the framework of spatial prediction, were mainly reflected in the spatial connectivity of the Ks-field. Ignoring the trend component and an arbitrary use of robust estimators, however, would have the most severe consequences in this respect. Regarding variogram modeling, I encouraged restricted maximum likelihood estimation because of its accuracy and independence on the selected lags needed for experimental variograms. The second study dealt with the Ks spatial-temporal pattern in the sequences of natural and man-made disturbances characteristic for the montane rainforest study area. To investigate the disturbance effects both on global means and the spatial structure of Ks, a combined design-and model-based sampling approach was used for field-measurements at soil depths of 12.5, 20, and 50 cm (n=30-150/depth) under landslides of different ages (2 and 8 years), under actively grazed pasture, fallows following pasture abandonment (2 to 25 years of age), and under natural forest. Concerning global means, our main findings were 1) global means of the soil permeability generally decrease with increasing soil depth; 2) no significant Ks differences can be observed among landslides and compared to the natural forest; 3) a distinct permeability decrease of two orders of magnitude occurs after forest conversion to pasture at shallow soil depths, and 4) the slow regeneration process after pasture abandonment requires at least one decade. Regarding the Ks spatial structure, we found that 1) disturbances affect the Ks spatial structure in the topsoil, and 2) the largest differences in spatial patterns are associated with the subsoil permeability. In summary, the regional landslide activity seems to affect soil hydrology to a marginal extend only, which is in contrast to the pronounced drop of Ks after forest conversion. We used this spatial-temporal information combined with local rain intensities to assess the partitioning of rainfall into vertical and lateral flowpaths under undisturbed, disturbed, and regenerating land-cover types in the third study. It turned out that 1) the montane rainforest is characterized by prevailing vertical flowpaths in the topsoil, which can switch to lateral directions below 20 cm depth for a small number of rain events, which may, however, transport a high portion of the annual runoff; 2) similar hydrological flowpaths occur under the landslides except for a somewhat higher probability of impermeable layer formation in the topsoil of a young landslide, and 3) pronounced differences in runoff components can be observed for the human disturbance sequence involving the development of near-surface impeding layers for 24, 44, and 8 \% of rain events for pasture, a two-year-old fallow, and a ten-year-old fallow, respectively.},
  language  = {en}
}