TY - GEN A1 - Langerwisch, Fanny A1 - Walz, Ariane A1 - Rammig, Anja A1 - Tietjen, Britta A1 - Thonicke, Kirsten A1 - Cramer, Wolfgang T1 - Deforestation in Amazonia impacts riverine carbon dynamics T2 - Postprints der Universität Potsdam : Mathematisch-Naturwissenschaftliche Reihe N2 - Fluxes of organic and inorganic carbon within the Amazon basin are considerably controlled by annual flooding, which triggers the export of terrigenous organic material to the river and ultimately to the Atlantic Ocean. The amount of carbon imported to the river and the further conversion, transport and export of it depend on temperature, atmospheric CO2, terrestrial productivity and carbon storage, as well as discharge. Both terrestrial productivity and discharge are influenced by climate and land use change. The coupled LPJmL and RivCM model system (Langerwisch et al., 2016) has been applied to assess the combined impacts of climate and land use change on the Amazon riverine carbon dynamics. Vegetation dynamics (in LPJmL) as well as export and conversion of terrigenous carbon to and within the river (RivCM) are included. The model system has been applied for the years 1901 to 2099 under two deforestation scenarios and with climate forcing of three SRES emission scenarios, each for five climate models. We find that high deforestation (business-as-usual scenario) will strongly decrease (locally by up to 90 %) riverine particulate and dissolved organic carbon amount until the end of the current century. At the same time, increase in discharge leaves net carbon transport during the first decades of the century roughly unchanged only if a sufficient area is still forested. After 2050 the amount of transported carbon will decrease drastically. In contrast to that, increased temperature and atmospheric CO2 concentration determine the amount of riverine inorganic carbon stored in the Amazon basin. Higher atmospheric CO2 concentrations increase riverine inorganic carbon amount by up to 20% (SRES A2). The changes in riverine carbon fluxes have direct effects on carbon export, either to the atmosphere via outgassing or to the Atlantic Ocean via discharge. The outgassed carbon will increase slightly in the Amazon basin, but can be regionally reduced by up to 60% due to deforestation. The discharge of organic carbon to the ocean will be reduced by about 40% under the most severe deforestation and climate change scenario. These changes would have local and regional consequences on the carbon balance and habitat characteristics in the Amazon basin itself as well as in the adjacent Atlantic Ocean. T3 - Zweitveröffentlichungen der Universität Potsdam : Mathematisch-Naturwissenschaftliche Reihe - 535 KW - Global vegetation model KW - Climate-Change KW - Brazilian Amazon KW - organic-matter KW - land-use KW - secondary forests KW - seed dispersal KW - Atlantic-Ocean KW - basin KW - CO2 Y1 - 2019 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus4-410225 SN - 1866-8372 IS - 535 ER - TY - JOUR A1 - Langerwisch, Fanny A1 - Walz, Ariane A1 - Rammig, Anja A1 - Tietjen, Britta A1 - Thonicke, Kirsten A1 - Cramer, Wolfgang T1 - Deforestation in Amazonia impacts riverine carbon dynamics JF - Earth system dynamics N2 - Fluxes of organic and inorganic carbon within the Amazon basin are considerably controlled by annual flooding, which triggers the export of terrigenous organic material to the river and ultimately to the Atlantic Ocean. The amount of carbon imported to the river and the further conversion, transport and export of it depend on temperature, atmospheric CO2, terrestrial productivity and carbon storage, as well as discharge. Both terrestrial productivity and discharge are influenced by climate and land use change. The coupled LPJmL and RivCM model system (Langerwisch et al., 2016) has been applied to assess the combined impacts of climate and land use change on the Amazon riverine carbon dynamics. Vegetation dynamics (in LPJmL) as well as export and conversion of terrigenous carbon to and within the river (RivCM) are included. The model system has been applied for the years 1901 to 2099 under two deforestation scenarios and with climate forcing of three SRES emission scenarios, each for five climate models. We find that high deforestation (business-as-usual scenario) will strongly decrease (locally by up to 90 %) riverine particulate and dissolved organic carbon amount until the end of the current century. At the same time, increase in discharge leaves net carbon transport during the first decades of the century roughly unchanged only if a sufficient area is still forested. After 2050 the amount of transported carbon will decrease drastically. In contrast to that, increased temperature and atmospheric CO2 concentration determine the amount of riverine inorganic carbon stored in the Amazon basin. Higher atmospheric CO2 concentrations increase riverine inorganic carbon amount by up to 20% (SRES A2). The changes in riverine carbon fluxes have direct effects on carbon export, either to the atmosphere via outgassing or to the Atlantic Ocean via discharge. The outgassed carbon will increase slightly in the Amazon basin, but can be regionally reduced by up to 60% due to deforestation. The discharge of organic carbon to the ocean will be reduced by about 40% under the most severe deforestation and climate change scenario. These changes would have local and regional consequences on the carbon balance and habitat characteristics in the Amazon basin itself as well as in the adjacent Atlantic Ocean. Y1 - 2016 U6 - https://doi.org/10.5194/esd-7-953-2016 SN - 2190-4979 SN - 2190-4987 VL - 7 SP - 953 EP - 968 PB - Copernicus CY - Göttingen ER - TY - JOUR A1 - Tietjen, Britta A1 - Jeltsch, Florian A1 - Zehe, Erwin A1 - Classen, Nikolaus A1 - Groengroeft, Alexander A1 - Schiffers, Katja A1 - Oldeland, Jens T1 - Effects of climate change on the coupled dynamics of water and vegetation in drylands N2 - Drylands worldwide are exposed to a highly variable environment and face a high risk of degradation. The effects of global climate change such as altered precipitation patterns and increased temperature leading to reduced water availability will likely increase this risk. At the same time, an elevated atmospheric CO2 level could mitigate the effects of reduced water availability by increasing the water use efficiency of plants. To prevent degradation of drylands, it is essential to understand the underlying processes that affect water availability and vegetation cover. Since water and vegetation are strongly interdependent in water-limited ecosystems, changes can lead to highly non- linear effects. We assess these effects by developing an ecohydrological model of soil moisture and vegetation cover. The water component of the model simulates the daily dynamics of surface water and water contents in two soil layers. Vegetation is represented by two functional types: shrubs and grasses. These compete for soil water and strongly influence hydrological processes. We apply the model to a Namibian thornbush savanna and evaluate the separate and combined effects of decreased annual precipitation, increased temperature, more variable precipitation and elevated atmospheric CO2 on soil moisture and on vegetation cover. The results show that two main factors control the response of plant types towards climate change, namely a change in water availability and a change in water allocation to a specific plant type. Especially, reduced competitiveness of grasses can lead to a higher risk of shrub encroachment in these systems. Y1 - 2010 UR - http://www3.interscience.wiley.com/journal/114209870/home U6 - https://doi.org/10.1002/Eco.70 SN - 1936-0584 ER - TY - JOUR A1 - Synodinos, Alexios D. A1 - Tietjen, Britta A1 - Jeltsch, Florian T1 - Facilitation in drylands: Modeling a neglected driver of savanna dynamics JF - Ecological modelling : international journal on ecological modelling and engineering and systems ecolog N2 - Our current understanding regarding the functioning of the savanna ecosystem describes savannas as either competition- or disturbance-dependent. Within this generalized view, the role and importance of facilitation have been mostly neglected. This study presents a mathematical model of savannas with coupled soil moisture-vegetation dynamics, which includes interspecific competition and environmental disturbance. We find that there exist environmental and climatic conditions where grass facilitation toward trees plays an important role in supporting tree cover and by extension preserving the savanna biome. We, therefore, argue that our theoretical results in combination with the first empirical studies on the subject should stimulate further research into the role of facilitation in the savanna ecosystem, particularly when analyzing the impact of past and projected climatic changes on it. (C) 2015 Elsevier B.V. All rights reserved. KW - Ecohydrological modeling KW - ODE model KW - Coexistence KW - Biome shifts KW - Fire KW - Grazing Y1 - 2015 U6 - https://doi.org/10.1016/j.ecolmodel.2015.02.015 SN - 0304-3800 SN - 1872-7026 VL - 304 SP - 11 EP - 21 PB - Elsevier CY - Amsterdam ER - TY - JOUR A1 - Fer, Istem A1 - Tietjen, Britta A1 - Jeltsch, Florian T1 - High-resolution modelling closes the gap between data and model simulations for Mid-Holocene and present-day biomes of East Africa JF - Palaeogeography, palaeoclimatology, palaeoecology : an international journal for the geo-sciences N2 - East Africa hosts a striking diversity of terrestrial ecosystems, which vary both in space and time due to complex regional topography and a dynamic climate. The structure and functioning of these ecosystems under this environmental setting can be studied with dynamic vegetation models (DVMs) in a spatially explicit way. Yet, regional applications of DVMs to East Africa are rare and a comprehensive validation of such applications is missing. Here, we simulated the present-day and mid-Holocene vegetation of East Africa with the DVM, LPJ-GUESS and we conducted an exhaustive comparison of model outputs with maps of potential modern vegetation distribution, and with pollen records of local change through time. Overall, the model was able to reproduce the observed spatial patterns of East African vegetation. To see whether running the model at higher spatial resolutions (10′ × 10′) contribute to resolve the vegetation distribution better and have a better comparison scale with the observational data (i.e. pollen data), we run the model with coarser spatial resolution (0.5° × 0.5°) for the present-day as well. Both the area- and point-wise comparison showed that a higher spatial resolution allows to better describe spatial vegetation changes induced by the complex topography of East Africa. Our analysis of the difference between modelled mid-Holocene and modern-day vegetation showed that whether a biome shifts to another is best explained by both the amount of change in precipitation it experiences and the amount of precipitation it received originally. We also confirmed that tropical forest biomes were more sensitive to a decrease in precipitation compared to woodland and savanna biomes and that Holocene vegetation changes in East Africa were driven not only by changes in annual precipitation but also by changes in its seasonality. KW - Dynamic vegetation models KW - Biome KW - Mid-Holocene KW - Leaf area index KW - Climate change KW - East Africa Y1 - 2016 U6 - https://doi.org/10.1016/j.palaeo.2015.12.001 SN - 0031-0182 SN - 1872-616X VL - 444 SP - 144 EP - 151 PB - Elsevier CY - Amsterdam ER - TY - JOUR A1 - Esther, Alexandra A1 - Groeneveld, Jürgen A1 - Enright, Neal J. A1 - Miller, Ben P. A1 - Lamont, Byron B. A1 - Perry, George L. W. A1 - Tietjen, Britta A1 - Jeltsch, Florian T1 - Low-dimensional trade-offs fail to explain richness and structure in species-rich plant communities JF - Theoretical ecology N2 - Mathematical models and ecological theory suggest that low-dimensional life history trade-offs (i.e. negative correlation between two life history traits such as competition vs. colonisation) may potentially explain the maintenance of species diversity and community structure. In the absence of trade-offs, we would expect communities to be dominated by 'super-types' characterised by mainly positive trait expressions. However, it has proven difficult to find strong empirical evidence for such trade-offs in species-rich communities. We developed a spatially explicit, rule-based and individual-based stochastic model to explore the importance of low-dimensional trade-offs. This model simulates the community dynamics of 288 virtual plant functional types (PFTs), each of which is described by seven life history traits. We consider trait combinations that fit into the trade-off concept, as well as super-types with little or no energy constraints or resource limitations, and weak PFTs, which do not exploit resources efficiently. The model is parameterised using data from a fire-prone, species-rich Mediterranean-type shrubland in southwestern Australia. We performed an exclusion experiment, where we sequentially removed the strongest PFT in the simulation and studied the remaining communities. We analysed the impact of traits on performance of PFTs in the exclusion experiment with standard and boosted regression trees. Regression tree analysis of the simulation results showed that the trade-off concept is necessary for PFT viability in the case of weak trait expression combinations such as low seed production or small seeds. However, species richness and diversity can be high despite the presence of super-types. Furthermore, the exclusion of super-types does not necessarily lead to a large increase in PFT richness and diversity. We conclude that low-dimensional trade-offs do not provide explanations for multi-species co-existence contrary to the prediction of many conceptual models. KW - Plant diversity KW - Plant functional types KW - Co-existence KW - Spatially explicit model KW - Individual-based model KW - CART KW - Regression tree analysis KW - Boosted regression tree Y1 - 2011 U6 - https://doi.org/10.1007/s12080-010-0092-y SN - 1874-1738 VL - 4 IS - 4 SP - 495 EP - 511 PB - Springer CY - Heidelberg ER - TY - JOUR A1 - Tietjen, Britta A1 - Huth, Andreas T1 - Modelling dynamics of managed tropical rainforests - An aggregated approach JF - Ecological modelling : international journal on ecological modelling and engineering and systems ecolog N2 - The overuse of rainforests in the last century and its consequences necessitate a rethinking of logging policies. To this end models have been developed to simulate rainforest dynamics and to allow optional management strategies to be evaluated. Parameterisation of presently existing models for a certain site needs a lot of work, thus the parameterisation effort is too high to apply the models to a wide range of rainforests. Hence, in this paper we introduce the simplified model FORREG using the knowledge we have gained from a more complex model, FORMIX3-Q. The FORREG model uses differential equations to determine the volume growth of three successional species groups. Parameterisation is simplified by a genetic algorithm, which determines the required internal model parameters from characteristics of the forest dynamics. The new model is employed to assess the sustainability of various logging policies in terms of yield and damage. Results for three forests are discussed: (1) the tropical lowland rain forest in the Deramakot Forest Reserve, (2) the Lambir National Park in Malaysia and (3) a subtropical forest in Paraguay. Our model reproduces both undisturbed forest dynamics and dynamics of logged forests simulated with FORMIX3-Q very well. However, the resultant volumes of yield and damage differ slightly from those gained by FORMIX3-Q if short logging cycles are simulated. Choosing longer logging cycles leads to a good correspondence of both models. For the Deramakot Forest Reserve different logging cycles are compared and discussed. (c) 2006 Elsevier B.V. All rights reserved. KW - aggregation KW - differential equation KW - forest model KW - genetic algorithm KW - logging KW - tropical rainforest Y1 - 2006 U6 - https://doi.org/10.1016/j.ecolmodel.2005.11.045 SN - 0304-3800 VL - 199 IS - 4 SP - 421 EP - 432 PB - Elsevier CY - Amsterdam ER - TY - JOUR A1 - Fer, Istem A1 - Tietjen, Britta A1 - Jeltsch, Florian A1 - Trauth, Martin H. T1 - Modelling vegetation change during Late Cenozoic uplift of the East African plateaus JF - Palaeogeography, palaeoclimatology, palaeoecology : an international journal for the geo-sciences N2 - The present-day vegetation in the tropics is mainly characterized by forests worldwide except in tropical East Africa, where forests only occur as patches at the coast and in the uplands. These forest patches result from the peculiar aridity that is linked to the uplift of the region during the Late Cenozoic. The Late Cenozoic vegetation history of East Africa is of particular interest as it has set the scene for the contemporary events in mammal and hominin evolution. In this study, we investigate the conditions under which these forest patches could have been connected, and a previous continuous forest belt could have extended and fragmented. We apply a dynamic vegetation model with a set of climatic scenarios in which we systematically alter the present-day environmental conditions such that they would be more favourable for a continuous forest belt in tropical East Africa. We consider varying environmental factors, namely temperature, precipitation and atmospheric CO2 concentrations. Our results show that all of these variables play a significant role in supporting the forest biomes and a continuous forest belt could have occurred under certain combinations of these settings. With our current knowledge of the palaeoenvironmental history of East Africa, it is likely that the region hosted these conditions during the Late Cenozoic. Recent improvements on environmental hypotheses of hominin evolution highlight the role of periods of short and extreme climate variability during the Late Cenozoic specific to East Africa in driving evolution. Our results elucidate how the forest biomes of East Africa can appear and disappear under fluctuating environmental conditions and demonstrate how this climate variability might be recognized on the biosphere level. KW - Dynamic vegetation models KW - Palaeovegetation KW - Evolution KW - Late Cenozoic KW - East Africa KW - Climate change Y1 - 2016 U6 - https://doi.org/10.1016/j.palaeo.2016.04.007 SN - 0031-0182 SN - 1872-616X VL - 467 SP - 120 EP - 130 PB - Elsevier CY - Amsterdam ER - TY - JOUR A1 - Karp, Daniel S. A1 - Tallis, Heather A1 - Sachse, Rene A1 - Halpern, Ben A1 - Thonicke, Kirsten A1 - Cramer, Wolfgang A1 - Mooney, Harold A1 - Polasky, Stephen A1 - Tietjen, Britta A1 - Waha, Katharina A1 - Walt, Ariane A1 - Wolny, Stacie T1 - National indicators for observing ecosystem service change JF - Global environmental change : human and policy dimensions N2 - Earth's life-support systems are in rapid decline, yet we have few metrics or indicators with which to track these changes. The world's governments are calling for biodiversity and ecosystem-service monitoring to guide and evaluate international conservation policy as well as to incorporate natural capital into their national accounts. The Group on Earth Observations Biodiversity Observation Network (GEO BON) has been tasked with setting up this monitoring system. Here we explore the immediate feasibility of creating a global ecosystem-service monitoring platform under the GEO BON framework through combining data from national statistics, global vegetation models, and production function models. We found that nine ecosystem services could be annually reported at a national scale in the short term: carbon sequestration, water supply for hydropower, and non-fisheries marine products, crop, livestock, game meat, fisheries, mariculture, and timber production. Reported changes in service delivery over time reflected ecological shocks (e.g., droughts and disease outbreaks), highlighting the immediate utility of this monitoring system. Our work also identified three opportunities for creating a more comprehensive monitoring system. First, investing in input data for ecological process models (e.g., global land-use maps) would allow many more regulating services to be monitored. Currently, only 1 of 9 services that can be reported is a regulating service. Second, household surveys and censuses could help evaluate how nature affects people and provides non-monetary benefits. Finally, to forecast the sustainability of service delivery, research efforts could focus on calculating the total remaining biophysical stocks of provisioning services. Regardless, we demonstrated that a preliminary ecosystem-service monitoring platform is immediately feasible. With sufficient international investment, the platform could evolve further into a much-needed system to track changes in our planet's life-support systems. (C) 2015 Elsevier Ltd. All rights reserved. KW - Ecosystem services KW - GEO BON KW - Global change KW - Monitoring KW - Process models Y1 - 2015 U6 - https://doi.org/10.1016/j.gloenvcha.2015.07.014 SN - 0959-3780 SN - 1872-9495 VL - 35 SP - 12 EP - 21 PB - Elsevier CY - Oxford ER - TY - JOUR A1 - Lohmann, Dirk A1 - Tietjen, Britta A1 - Blaum, Niels A1 - Joubert, David Francois A1 - Jeltsch, Florian T1 - Prescribed fire as a tool for managing shrub encroachment in semi-arid savanna rangelands JF - Journal of arid environments N2 - Savanna rangelands worldwide are threatened by shrub encroachment, i.e. the increase of woody plant species at the cost of perennial grasses, causing a strong decline in the productivity of domestic livestock production. Although recent studies indicate that fire might be of great importance for semi-arid and arid savanna dynamics, it is largely not applied in the management of semi-arid rangelands especially with regard to woody plant control. We used the eco-hydrological savanna model EcoHyD to simulate the effects of different fire management strategies on semi-arid savanna vegetation and to assess their longterm suitability for semi-arid rangeland management. Simulation results show that prescribed fires, timed to kill tree seedlings prevented shrub encroachment for a broad range of livestock densities while the possible maximum long-term cattle densities on the simulated semi-arid rangeland in Namibia increased by more than 30%. However, when grazing intensity was too high, fire management failed in preventing shrub encroachment. Our findings indicate that with regard to fire management a clear distinction between mesic and more arid savannas is necessary: While the frequency of fires is of relevance for mesic savannas, we recommend a fire management focussing on the timing of fire for semi-arid and arid savannas. (C) 2014 Elsevier Ltd. All rights reserved. KW - Acacia mellifera KW - Bush encroachment KW - Dry land degradation KW - Rangeland management KW - Simulation model KW - Southern Africa Y1 - 2014 U6 - https://doi.org/10.1016/j.jaridenv.2014.04.003 SN - 0140-1963 SN - 1095-922X VL - 107 SP - 49 EP - 56 PB - Elsevier CY - London ER -