TY - JOUR A1 - Blaum, Niels A1 - Tietjen, Britta A1 - Rossmanith, Eva T1 - The impact of livestock husbandry on small- and medium-sized carnivores in Kalahari savannah rangelands N2 - We analyzed relative sensitivities of small- and medium-sized carnivores to livestock husbandry (stocking rates and predator control) in Kalahari, South Africa, rangelands at a regional scale. We monitored small carnivores using track counts on 22 Kalahari farms across a land-use gradient ranging from low to high stocking rates and also interviewed each farm manager to identify farmers" perception of small carnivores as potential predators for livestock. We recorded 12 species of small- and medium-sized carnivores across 22 Kalahari farms. Stocking rate was the most important driving variable for local carnivore abundance. Abundance of all species was lowest on farms where stocking rate was high. Most farm managers perceived medium-sized carnivores, in particular, African wildcat (Felis silvestris lybica), black-backed jackal (Canis mesomelas), and caracal (Caracal caracal), as potential predators of livestock. Multiple regression analysis shows that black-backed jackal, African wildcat, and caracal were negatively affected by predator control measures, whereas bat-eared fox (Otocyon megalotis), cape fox (Vulpes chama), and small-spotted genet (Genetta genetta) were positively affected. Our results show a need for expanding research and conservation activities toward small- and medium-sized carnivores in southern African savannah rangelands. We, therefore, suggest developing a monitoring program combining passive tracking with indigenous knowledge of local Khoisan Bushmen to monitor carnivore populations, and we recommend additional predator removal experiments that manipulate predator densities. Y1 - 2009 UR - http://www.wildlifejournals.org/perlserv/?request=index-html&ct=1 U6 - https://doi.org/10.2193/2008-034 SN - 0022-541X 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 - 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 - 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 - Fer, Istem A1 - Tietjen, Britta A1 - Jeltsch, Florian A1 - Wolff, Christian Michael T1 - The influence of El Nino-Southern Oscillation regimes on eastern African vegetation and its future implications under the RCP8.5 warming scenario JF - Biogeosciences N2 - The El Nino-Southern Oscillation (ENSO) is the main driver of the interannual variability in eastern African rainfall, with a significant impact on vegetation and agriculture and dire consequences for food and social security. In this study, we identify and quantify the ENSO contribution to the eastern African rainfall variability to forecast future eastern African vegetation response to rainfall variability related to a predicted intensified ENSO. To differentiate the vegetation variability due to ENSO, we removed the ENSO signal from the climate data using empirical orthogonal teleconnection (EOT) analysis. Then, we simulated the ecosystem carbon and water fluxes under the historical climate without components related to ENSO teleconnections. We found ENSO-driven patterns in vegetation response and confirmed that EOT analysis can successfully produce coupled tropical Pacific sea surface temperature-eastern African rainfall teleconnection from observed datasets. We further simulated eastern African vegetation response under future climate change as it is projected by climate models and under future climate change combined with a predicted increased ENSO intensity. Our EOT analysis highlights that climate simulations are still not good at capturing rainfall variability due to ENSO, and as we show here the future vegetation would be different from what is simulated under these climate model outputs lacking accurate ENSO contribution. We simulated considerable differences in eastern African vegetation growth under the influence of an intensified ENSO regime which will bring further environmental stress to a region with a reduced capacity to adapt effects of global climate change and food security. Y1 - 2017 U6 - https://doi.org/10.5194/bg-14-4355-2017 SN - 1726-4170 SN - 1726-4189 VL - 14 SP - 4355 EP - 4374 PB - Copernicus CY - Göttingen ER - TY - JOUR A1 - Fer, Istem A1 - Tietjen, Britta A1 - Jeltsch, Florian A1 - Wolff, Christian Michael T1 - The influence of El Nino-Southern Oscillation regimes on eastern African vegetation and its future implications under the RCP8.5 warming scenario JF - Biogeosciences N2 - The El Nino-Southern Oscillation (ENSO) is the main driver of the interannual variability in eastern African rainfall, with a significant impact on vegetation and agriculture and dire consequences for food and social security. In this study, we identify and quantify the ENSO contribution to the eastern African rainfall variability to forecast future eastern African vegetation response to rainfall variability related to a predicted intensified ENSO. To differentiate the vegetation variability due to ENSO, we removed the ENSO signal from the climate data using empirical orthogonal teleconnection (EOT) analysis. Then, we simulated the ecosystem carbon and water fluxes under the historical climate without components related to ENSO teleconnections. We found ENSO-driven patterns in vegetation response and confirmed that EOT analysis can successfully produce coupled tropical Pacific sea surface temperature-eastern African rainfall teleconnection from observed datasets. We further simulated eastern African vegetation response under future climate change as it is projected by climate models and under future climate change combined with a predicted increased ENSO intensity. Our EOT analysis highlights that climate simulations are still not good at capturing rainfall variability due to ENSO, and as we show here the future vegetation would be different from what is simulated under these climate model outputs lacking accurate ENSO contribution. We simulated considerable differences in eastern African vegetation growth under the influence of an intensified ENSO regime which will bring further environmental stress to a region with a reduced capacity to adapt effects of global climate change and food security. Y1 - 2017 U6 - https://doi.org/10.5194/bg-14-4355-2017 SN - 1726-4170 SN - 1726-4189 VL - 14 IS - 18 SP - 4355 EP - 4374 PB - Copernicus CY - Katlenburg-Lindau ER - TY - GEN A1 - Fer, Istem A1 - Tietjen, Britta A1 - Jeltsch, Florian A1 - Wolff, Christian Michael T1 - The influence of El Nino-Southern Oscillation regimes on eastern African vegetation and its future implications under the RCP8.5 warming scenario N2 - The El Nino-Southern Oscillation (ENSO) is the main driver of the interannual variability in eastern African rainfall, with a significant impact on vegetation and agriculture and dire consequences for food and social security. In this study, we identify and quantify the ENSO contribution to the eastern African rainfall variability to forecast future eastern African vegetation response to rainfall variability related to a predicted intensified ENSO. To differentiate the vegetation variability due to ENSO, we removed the ENSO signal from the climate data using empirical orthogonal teleconnection (EOT) analysis. Then, we simulated the ecosystem carbon and water fluxes under the historical climate without components related to ENSO teleconnections. We found ENSO-driven patterns in vegetation response and confirmed that EOT analysis can successfully produce coupled tropical Pacific sea surface temperature-eastern African rainfall teleconnection from observed datasets. We further simulated eastern African vegetation response under future climate change as it is projected by climate models and under future climate change combined with a predicted increased ENSO intensity. Our EOT analysis highlights that climate simulations are still not good at capturing rainfall variability due to ENSO, and as we show here the future vegetation would be different from what is simulated under these climate model outputs lacking accurate ENSO contribution. We simulated considerable differences in eastern African vegetation growth under the influence of an intensified ENSO regime which will bring further environmental stress to a region with a reduced capacity to adapt effects of global climate change and food security. T3 - Zweitveröffentlichungen der Universität Potsdam : Mathematisch-Naturwissenschaftliche Reihe - 394 Y1 - 2017 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus4-403853 ER - TY - JOUR A1 - Guo, Tong A1 - Lohmann, Dirk A1 - Ratzmann, Gregor A1 - Tietjen, Britta T1 - Response of semi-arid savanna vegetation composition towards grazing along a precipitation gradient-The effect of including plant heterogeneity into an ecohydrological savanna model JF - Ecological modelling : international journal on ecological modelling and engineering and systems ecolog N2 - Ecohydrological models of savanna rangeland systems typically aggregate plant species to very broad plant functional types (PFTs), which are characterized by their trait combinations. However, neglecting trait variability within modelled PFTs may hamper our ability to understand the effects of climate or land use change on vegetation composition and thus on ecosystem processes. In this study we extended and parameterized the ecohydrological savanna model EcoHyD, which originally considered only three broad PFTs (perennial grasses, annuals and shrubs). We defined several sub-types of perennial grasses (sub-PFTs) to assess the effect of environmental conditions on vegetation composition and ecosystem functioning. These perennial sub-PFTs are defined by altering distinct trait values based on a trade-off approach for (i) the longevity of plants and (ii) grazing-resistance. We find that increasing grazing intensity leads to a dominance of the fast-growing and short-lived perennial grass type as well as a dominance of the poorly palatable grass type. Increasing precipitation dampens the magnitude of grazing-induced shifts between perennial grass types. The diversification of perennial grass PFTs generally increases the total perennial grass cover and ecosystem water use efficiency, but does not protect the community from shrub encroachment. We thus demonstrate that including trait heterogeneity into ecosystem models will allow for an improved representation of ecosystem responses to environmental change in savannas. This will help to better assess how ecosystem functions might be impacted under future conditions. (C) 2016 Elsevier B.V. All rights reserved. KW - Plant functional types KW - Trait heterogeneity KW - Rangeland management KW - Precipitation gradient KW - Livestock KW - Ecosystem functioning Y1 - 2016 U6 - https://doi.org/10.1016/j.ecolmodel.2016.01.004 SN - 0304-3800 SN - 1872-7026 VL - 325 SP - 47 EP - 56 PB - Elsevier CY - Amsterdam ER - TY - JOUR A1 - Guo, Tong A1 - Weise, Hanna A1 - Fiedler, Sebastian A1 - Lohmann, Dirk A1 - Tietjen, Britta T1 - The role of landscape heterogeneity in regulating plant functional diversity under different precipitation and grazing regimes in semi-arid savannas JF - Ecological modelling : international journal on ecological modelling and engineering and systems ecolog N2 - 1. Savanna systems exhibit a high plant functional diversity. While aridity and livestock grazing intensity have been widely discussed as drivers of savanna vegetation composition, physical soil properties have received less attention. Since savannas can show local differences in soil properties, these might act as environmental filters and affect plant diversity and ecosystem functioning at the patch scale. However, research on the link between savanna vegetation diversity and ecosystem function is widely missing. 2. In this study, we aim at understanding the impact of local heterogeneity in soil conditions on plant diversity and on ecosystem functions. For this, we used the ecohydrological savanna model EcoHyD. The model simulates the fate of multiple plant functional types and their interactions with local biotic and abiotic conditions. We applied the model to a set of different landscapes under a wide range of livestock grazing and precipitation scenarios to assess the impact of local heterogeneity in soil conditions on the composition and diversity of plant functional types and on ecosystem functions. 3. Comparisons between homogeneous and heterogeneous landscapes revealed that landscape soil heterogeneity allowed for a higher functional diversity of vegetation under conditions of high competition, i.e. scenarios of low grazing stress. However, landscape heterogeneity did not have this effect under low grazing stress in combination with high mean annual precipitation. Further, landscape heterogeneity led to a higher community biomass, especially for lower rainfall conditions, but also dependent on grazing stress. Total transpiration of the plant community decreased in heterogeneous landscapes under arid conditions. 4. This study highlights that local soil conditions interact with precipitation and grazing in driving savanna vegetation. It clearly shows that vegetation diversity and resulting ecosystem functioning can be driven by landscape heterogeneity. We therefore suggest that future research on ecosystem functioning of savanna systems should focus on the links between local environmental conditions via plant functional diversity to ecosystem functioning. KW - Plant functional type KW - Trait diversity KW - Ecosystem functioning KW - Plant coexistence KW - Soil texture KW - Ecohydrological model Y1 - 2018 U6 - https://doi.org/10.1016/j.ecolmodel.2018.04.009 SN - 0304-3800 SN - 1872-7026 VL - 379 SP - 1 EP - 9 PB - Elsevier CY - Amsterdam ER - TY - JOUR A1 - Irob, Katja A1 - Blaum, Niels A1 - Baldauf, Selina A1 - Kerger, Leon A1 - Strohbach, Ben A1 - Kanduvarisa, Angelina A1 - Lohmann, Dirk A1 - Tietjen, Britta T1 - Browsing herbivores improve the state and functioning of savannas BT - A model assessment of alternative land-use strategies JF - Ecology and evolution N2 - Changing climatic conditions and unsustainable land use are major threats to savannas worldwide. Historically, many African savannas were used intensively for livestock grazing, which contributed to widespread patterns of bush encroachment across savanna systems. To reverse bush encroachment, it has been proposed to change the cattle-dominated land use to one dominated by comparatively specialized browsers and usually native herbivores. However, the consequences for ecosystem properties and processes remain largely unclear. We used the ecohydrological, spatially explicit model EcoHyD to assess the impacts of two contrasting, herbivore land-use strategies on a Namibian savanna: grazer- versus browser-dominated herbivore communities. We varied the densities of grazers and browsers and determined the resulting composition and diversity of the plant community, total vegetation cover, soil moisture, and water use by plants. Our results showed that plant types that are less palatable to herbivores were best adapted to grazing or browsing animals in all simulated densities. Also, plant types that had a competitive advantage under limited water availability were among the dominant ones irrespective of land-use scenario. Overall, the results were in line with our expectations: under high grazer densities, we found heavy bush encroachment and the loss of the perennial grass matrix. Importantly, regardless of the density of browsers, grass cover and plant functional diversity were significantly higher in browsing scenarios. Browsing herbivores increased grass cover, and the higher total cover in turn improved water uptake by plants overall. We concluded that, in contrast to grazing-dominated land-use strategies, land-use strategies dominated by browsing herbivores, even at high herbivore densities, sustain diverse vegetation communities with high cover of perennial grasses, resulting in lower erosion risk and bolstering ecosystem services. KW - browsing KW - ecohydrology KW - land use KW - plant community KW - savanna KW - wildlife KW - management Y1 - 2022 U6 - https://doi.org/10.1002/ece3.8715 SN - 2045-7758 VL - 12 IS - 3 PB - Wiley CY - Hoboken 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 - 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 - Lohmann, Dirk A1 - Guo, Tong A1 - Tietjen, Britta T1 - Zooming in on coarse plant functional types-simulated response of savanna vegetation composition in response to aridity and grazing JF - Theoretical ecology N2 - Precipitation and land use in terms of livestock grazing have been identified as two of the most important drivers structuring the vegetation composition of semi-arid and arid savannas. Savanna research on the impact of these drivers has widely applied the so-called plant functional type (PFT) approach, grouping the vegetation into two or three broad types (here called meta-PFTs): woody plants and grasses, which are sometimes divided into perennial and annual grasses. However, little is known about the response of functional traits within these coarse types towards water availability or livestock grazing. In this study, we extended an existing eco-hydrological savanna vegetation model to capture trait diversity within the three broad meta-PFTs to assess the effects of both grazing and mean annual precipitation (MAP) on trait composition along a gradient of both drivers. Our results show a complex pattern of trait responses to grazing and aridity. The response differs for the three meta-PFTs. From our findings, we derive that trait responses to grazing and aridity for perennial grasses are similar, as suggested by the convergence model for grazing and aridity. However, we also see that this only holds for simulations below a MAP of 500 mm. This combined with the finding that trait response differs between the three meta-PFTs leads to the conclusion that there is no single, universal trait or set of traits determining the response to grazing and aridity. We finally discuss how simulation models including trait variability within meta-PFTs are necessary to understand ecosystem responses to environmental drivers, both locally and globally and how this perspective will help to extend conceptual frameworks of other ecosystems to savanna research. KW - Traits KW - Dryland KW - Degradation KW - Shrub encroachment KW - Simulation KW - Eco-hydrological model KW - EcoHyD Y1 - 2018 U6 - https://doi.org/10.1007/s12080-017-0356-x SN - 1874-1738 SN - 1874-1746 VL - 11 IS - 2 SP - 161 EP - 173 PB - Springer CY - Heidelberg ER - TY - JOUR A1 - Lohmann, Dirk A1 - Tietjen, Britta A1 - Blaum, Niels A1 - Joubert, David F. A1 - Jeltsch, Florian T1 - Shifting thresholds and changing degradation patterns: climate change effects on the simulated long-term response of a semi-arid savanna to grazing JF - Journal of applied ecology : an official journal of the British Ecological Society N2 - 1. The complex, nonlinear response of dryland systems to grazing and climatic variations is a challenge to management of these lands. Predicted climatic changes will impact the desertification of drylands under domestic livestock production. Consequently, there is an urgent need to understand the response of drylands to grazing under climate change. 2. We enhanced and parameterized an ecohydrological savanna model to assess the impacts of a range of climate change scenarios on the response of a semi-arid African savanna to grazing. We focused on the effects of temperature and CO2 level increase in combination with changes in inter- and intra-annual precipitation patterns on the long-term dynamics of three major plant functional types. 3. We found that the capacity of the savanna to sustain livestock grazing was strongly influenced by climate change. Increased mean annual precipitation and changes in intra-annual precipitation pattern have the potential to slightly increase carrying capacities of the system. In contrast, decreased precipitation, higher interannual variation and temperature increase are leading to a severe decline of carrying capacities owing to losses of the perennial grass biomass. 4. Semi-arid rangelands will be at lower risk of shrub encroachment and encroachment will be less intense under future climatic conditions. This finding holds in spite of elevated levels of atmospheric CO2 and irrespective of changes in precipitation pattern, because of the drought sensitivity of germination and establishment of encroaching species. 5. Synthesis and applications. Changes in livestock carrying capacities, both positive and negative, mainly depend on the highly uncertain future rainfall conditions. However, independent of the specific changes, shrub encroachment becomes less likely and in many cases less severe. Thus, managers of semi-arid rangelands should shift their focus from woody vegetation towards perennial grass species as indicators for rangeland degradation. Furthermore, the resulting reduced competition from woody vegetation has the potential to facilitate ecosystem restoration measures such as re-introduction of desirable plant species that are only little promising or infeasible under current climatic conditions. On a global scale, the reductions in standing biomass resulting from altered degradation dynamics of semi-arid rangelands can have negative impacts on carbon sequestration. KW - CO2 increase KW - demographic bottleneck KW - ecohydrology KW - grid-based simulation model KW - livestock KW - precipitation pattern KW - savanna resilience KW - shrub encroachment KW - soil moisture KW - sustainable rangeland management Y1 - 2012 U6 - https://doi.org/10.1111/j.1365-2664.2012.02157.x SN - 0021-8901 VL - 49 IS - 4 SP - 814 EP - 823 PB - Wiley-Blackwell CY - Hoboken 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 - TY - JOUR A1 - Müller, Eva Nora A1 - van Schaik, Loes A1 - Blume, Theresa A1 - Bronstert, Axel A1 - Carus, Jana A1 - Fleckenstein, Jan H. A1 - Fohrer, Nicola A1 - Geissler, Katja A1 - Gerke, Horst H. A1 - Gräff, Thomas A1 - Hesse, Cornelia A1 - Hildebrandt, Anke A1 - Hölker, Franz A1 - Hunke, Philip A1 - Körner, Katrin A1 - Lewandowski, Jörg A1 - Lohmann, Dirk A1 - Meinikmann, Karin A1 - Schibalski, Anett A1 - Schmalz, Britta A1 - Schröder-Esselbach, Boris A1 - Tietjen, Britta T1 - Scales, key aspects, feedbacks and challenges of ecohydrological research in Germany JF - Hydrologie und Wasserbewirtschaftung N2 - Ecohydrology analyses the interactions of biotic and abiotic aspects of our ecosystems and landscapes. It is a highly diverse discipline in terms of its thematic and methodical research foci. This article gives an overview of current German ecohydrological research approaches within plant-animal-soil-systems, meso-scale catchments and their river networks, lake systems, coastal areas and tidal rivers. It discusses their relevant spatial and temporal process scales and different types of interactions and feedback dynamics between hydrological and biotic processes and patterns. The following topics are considered key challenges: innovative analysis of the interdisciplinary scale continuum, development of dynamically coupled model systems, integrated monitoring of coupled processes at the interface and transition from basic to applied ecohydrological science to develop sustainable water and land resource management strategies under regional and global change. KW - Coastal regions KW - drylands KW - ecohydrological modelling KW - feedback KW - hyporheic zone KW - meso-scale ecosystems KW - plant-animal-soil-system KW - river networks Y1 - 2014 U6 - https://doi.org/10.5675/HyWa_2014,4_2 SN - 1439-1783 VL - 58 IS - 4 SP - 221 EP - 240 PB - Bundesanst. für Gewässerkunde CY - Koblenz ER - TY - JOUR A1 - Schiffers, Katja A1 - Tielboerger, Katja A1 - Tietjen, Britta A1 - Jeltsch, Florian T1 - Root plasticity buffers competition among plants theory meets experimental data JF - Ecology : a publication of the Ecological Society of America N2 - Morphological plasticity is a striking characteristic of plants in natural communities. In the context of foraging behavior particularly, root plasticity has been documented for numerous species. Root plasticity is known to mitigate competitive interactions by reducing the overlap of the individuals' rhizospheres. But despite its obvious effect on resource acquisition, plasticity has been generally neglected in previous empirical and theoretical studies estimating interaction intensity among plants. In this study, we developed a semi-mechanistic model that addresses this shortcoming by introducing the idea of compensatory growth into the classical-zone-of influence (ZOI) and field-of-neighborhood (FON) approaches. The model parameters describing the belowground plastic sphere of influence (PSI) were parameterized using data from an accompanying field experiment. Measurements of the uptake of a stable nutrient analogue at distinct distances to the neighboring plants showed that the study species responded plastically to belowground competition by avoiding overlap of individuals' rhizospheres. An unexpected finding was that the sphere of influence of the study species Bromus hordeaceus could be best described by a unimodal function of distance to the plant's center and not with a continuously decreasing function as commonly assumed. We employed the parameterized model to investigate the interplay between plasticity and two other important factors determining the intensity of competitive interactions: overall plant density and the distribution of individuals in space. The simulation results confirm that the reduction of competition intensity due to morphological plasticity strongly depends on the spatial structure of the competitive environment. We advocate the use of semi-mechanistic simulations that explicitly consider morphological plasticity to improve our mechanistic understanding of plant interactions. KW - Bromus hordeaceus KW - competition intensity KW - morphological plasticity KW - nutrient analogues KW - plant density KW - PSI (plastic sphere of influence) KW - zone-of-influence model Y1 - 2011 SN - 0012-9658 VL - 92 IS - 3 SP - 610 EP - 620 PB - Wiley CY - Washington 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 - Synodinos, Alexis D. A1 - Tietjen, Britta A1 - Lohmann, Dirk A1 - Jeltsch, Florian T1 - The impact of inter-annual rainfall variability on African savannas changes with mean rainfall JF - Journal of theoretical biology N2 - Savannas are mixed tree-grass ecosystems whose dynamics are predominantly regulated by resource competition and the temporal variability in climatic and environmental factors such as rainfall and fire. Hence, increasing inter-annual rainfall variability due to climate change could have a significant impact on savannas. To investigate this, we used an ecohydrological model of stochastic differential equations and simulated African savanna dynamics along a gradient of mean annual rainfall (520–780 mm/year) for a range of inter-annual rainfall variabilities. Our simulations produced alternative states of grassland and savanna across the mean rainfall gradient. Increasing inter-annual variability had a negative effect on the savanna state under dry conditions (520 mm/year), and a positive effect under moister conditions (580–780 mm/year). The former resulted from the net negative effect of dry and wet extremes on trees. In semi-arid conditions (520 mm/year), dry extremes caused a loss of tree cover, which could not be recovered during wet extremes because of strong resource competition and the increased frequency of fires. At high mean rainfall (780 mm/year), increased variability enhanced savanna resilience. Here, resources were no longer limiting and the slow tree dynamics buffered against variability by maintaining a stable population during ‘dry’ extremes, providing the basis for growth during wet extremes. Simultaneously, high rainfall years had a weak marginal benefit on grass cover due to density-regulation and grazing. Our results suggest that the effects of the slow tree and fast grass dynamics on tree-grass interactions will become a major determinant of the savanna vegetation composition with increasing rainfall variability. KW - Rainfall variability KW - Savanna-grassland bistability KW - Stochastic differential equations KW - Coexistence mechanisms KW - Fire Y1 - 2017 U6 - https://doi.org/10.1016/j.jtbi.2017.10.019 SN - 0022-5193 SN - 1095-8541 VL - 437 SP - 92 EP - 100 PB - Elsevier Ltd. CY - London ER -