@article{GeisslerFiedlerNietal.2019, author = {Geissler, Katja and Fiedler, Sebastian and Ni, Jian and Herzschuh, Ulrike and Jeltsch, Florian}, title = {Combined effects of grazing and climate warming drive shrub dominance on the Tibetan Plateau}, series = {The Rangeland journal}, volume = {41}, journal = {The Rangeland journal}, number = {5}, publisher = {CSIRO Publishing}, address = {Collingwood}, issn = {1036-9872}, doi = {10.1071/RJ19027}, pages = {425 -- 439}, year = {2019}, abstract = {Encroachment of shrubs into the unique pastoral grassland ecosystems of the Tibetan Plateau has significant impact on ecosystem services, especially forage production. We developed a process-based ecohydrological model to identify the relative importance of the main drivers of shrub encroachment for the alpine meadows within the Qinghai province. Specifically, we explored the effects of summer livestock grazing (intensity and type of livestock) together with the effects of climate warming, including interactions between herbaceous and woody vegetation and feedback loops between soil, water and vegetation. Under current climatic conditions and a traditional herd composition, an increasing grazing intensity above a threshold value of 0.32 +/- 0.10 large stock units (LSU) ha(-1) day(-1) changes the vegetation composition from herbaceous towards a woody and bare soil dominated system. Very high grazing intensity (above 0.8 LSU ha(-1) day(-1)) leads to a complete loss of any vegetation. Under warmer conditions, the vegetation showed a higher resilience against livestock farming. This resilience is enhanced when the herd has a higher browser : grazer ratio. A cooler climate has a shrub encroaching effect, whereas warmer conditions increase the cover of the herbaceous vegetation. This effect was primarily due to season length and an accompanied competitive loss of slower growing shrubs, rather than evaporative water loss leading to less soil water in deeper soil layers for deeper rooting shrubs. If climate warming is driving current shrub encroachment, we conclude it is only indirectly so. It would be manifest by an advancing shrubline and could be regarded as a climatic escape of specific shrub species such as Potentilla fruticosa. Under the recent high intensity of grazing, only herding by more browsing animals can potentially prevent both shrub encroachment and the complete loss of herbaceous vegetation.}, language = {en} } @article{LohmannFalkGeissleretal.2014, author = {Lohmann, Dirk and Falk, Thomas and Geissler, Katja and Blaum, Niels and Jeltsch, Florian}, title = {Determinants of semi-arid rangeland management in a land reform setting in Namibia}, series = {Journal of arid environments}, volume = {100}, journal = {Journal of arid environments}, publisher = {Elsevier}, address = {London}, issn = {0140-1963}, doi = {10.1016/j.jaridenv.2013.10.005}, pages = {23 -- 30}, year = {2014}, abstract = {To assess the ecological and economic implications of the redistributive land reform in semi-arid Namibia, we investigated to what extent land reform beneficiaries adjust herd size and herd composition according to environmental (rainfall, vegetation) and economic variables (herd size, financial assets, running costs). We performed model-based role-plays with Namibian land reform beneficiaries, simulating 10 years of rangeland management. Our study revealed that the farmers surveyed mainly manage their herds according to their economic situation (herd size and account balance) but do not take environmental variability (rainfall and vegetation) into account. Further, our results indicate that, due to financial pressure, farmers are not able to apply their desired management strategies, and that owners of small farms face a higher risk of economic failure. However, farmers apply rather conservative and constant stocking rates and will thus, given the current economic limitations, likely not contribute to semi-arid savanna degradation. We conclude that land reform beneficiaries need support to be able to apply straightforward and efficient management strategies. This could be achieved by facilitating cooperation between small farming businesses and by supporting initial investment in productive cattle herds at the time of redistribution of the land.}, language = {en} } @article{WeissSchalowJeltschetal.2019, author = {Weiss, Lina and Schalow, Linda and Jeltsch, Florian and Geissler, Katja}, title = {Experimental evidence for root competition effects on community evenness in one of two phytometer species}, series = {Journal of plant ecology}, volume = {12}, journal = {Journal of plant ecology}, number = {2}, publisher = {Oxford Univ. Press}, address = {Oxford}, issn = {1752-9921}, doi = {10.1093/jpe/rty021}, pages = {281 -- 291}, year = {2019}, abstract = {Aims Plant-plant interactions, being positive or negative, are recognized to be key factors in structuring plant communities. However, it is thought that root competition may be less important than shoot competition due to greater size symmetry belowground. Because direct experimental tests on the importance of root competition are scarce, we aim at elucidating whether root competition may have direct or indirect effects on community structure. Indirect effects may occur by altering the overall size asymmetry of competition through root-shoot competitive interactions. Methods We used a phytometer approach to examine the effects of root, shoot and total competition intensity and importance on evenness of experimental plant communities. Thereby two different phytometer species, Festuca brevipila and Dianthus carthusianorum, were grown in small communities of six grassland species over three levels of light and water availability, interacting with neighbouring shoots, roots, both or not at all. Important Findings We found variation in community evenness to be best explained if root and shoot (but not total) competition were considered. However, the effects were species specific: in Dianthus communities increasing root competition increased plant community evenness, while in Festuca communities shoot competition was the driving force of this evenness response. Competition intensities were influenced by environmental conditions in Dianthus, but not in Festuca phytometer plants. While we found no evidence for root-shoot interactions for neither phytometer species root competition in Dianthus communities led to increased allocation to shoots, thereby increasing the potential ability to perform in size-asymmetric competition for light. Our experiment demonstrates the potential role of root competition in structuring plant communities.}, language = {en} } @article{GeisslerGzik2010, author = {Geissler, Katja and Gzik, Axel}, title = {Germination ecology of three endangered river corridor plants in relation to their preferred occurrence}, issn = {0367-2530}, doi = {10.1016/j.flora.2010.04.008}, year = {2010}, abstract = {As a contribution to conservation, we investigated germination requirements of three perennial, endangered river corridor plants of Central European lowlands coexisting in subcontinental flood meadows, but preferring particular zones of decreasing flooding frequency and duration along the elevational gradient of the banks. It was hypothesized that the species have specific germination requirements to respond successfully to open patch creation depending on their occurrence along the gradient of spring flooding in the field. This study involved controlled experiments and phenological studies. Juncus atratus and Gratiola officinalis, which frequently occupy flooded, naturally disturbed sites, have an absolute light requirement for germination, typical of pioneer species. Summer-dispersed, non-dormant seeds off. atratus did hardly germinate at high temperatures and lacked a gap sensitivity based on temperature fluctuation. Since the temperature amplitude decreases beneath an insulating cover of vegetation or water, seeds seem to be prepared for rapid germination at open, wet, maybe even inundated sites. Late-summer-dispersed seeds of G. officinalis were in a state of conditional primary dormancy. Dormancy could be completely broken by cold-wet stratification, indicating spring germination. Similar to J. atratus, daily temperature fluctuations did not control germination at suitable microsites. In Cnidium dubium that occurs at higher elevated sites, the level of primary dormancy of seeds was sufficient to prevent germination following dispersal, but the level was dependent on the year of harvest. Buried seeds showed an annual dormancy/conditional dormancy cycle. Dormancy was only partially broken by cold- wet stratification. It was completely broken by application of a high concentration of gibberellic acid. C. dubium had no absolute light requirement for germination, but it was stimulated by high light levels and in contrast to the other two species, seeds were stimulated by daily temperature fluctuations. Germination would therefore be maximized by zaps in early spring when the flooding water has receded. Re-entering dormancy in the late spring fails to support that germination occurs immediately after early-summer mowing - an important factor at subcontinental flood meadows.}, language = {en} } @article{JeltschBlaumBroseetal.2013, author = {Jeltsch, Florian and Blaum, Niels and Brose, Ulrich and Chipperfield, Joseph D. and Clough, Yann and Farwig, Nina and Geissler, Katja and Graham, Catherine H. and Grimm, Volker and Hickler, Thomas and Huth, Andreas and May, Felix and Meyer, Katrin M. and Pagel, J{\"o}rn and Reineking, Bj{\"o}rn and Rillig, Matthias C. and Shea, Katriona and Schurr, Frank Martin and Schroeder, Boris and Tielb{\"o}rger, Katja and Weiss, Lina and Wiegand, Kerstin and Wiegand, Thorsten and Wirth, Christian and Zurell, Damaris}, title = {How can we bring together empiricists and modellers in functional biodiversity research?}, series = {Basic and applied ecology : Journal of the Gesellschaft f{\"u}r {\"O}kologie}, volume = {14}, journal = {Basic and applied ecology : Journal of the Gesellschaft f{\"u}r {\"O}kologie}, number = {2}, publisher = {Elsevier}, address = {Jena}, issn = {1439-1791}, doi = {10.1016/j.baae.2013.01.001}, pages = {93 -- 101}, year = {2013}, abstract = {Improving our understanding of biodiversity and ecosystem functioning and our capacity to inform ecosystem management requires an integrated framework for functional biodiversity research (FBR). However, adequate integration among empirical approaches (monitoring and experimental) and modelling has rarely been achieved in FBR. We offer an appraisal of the issues involved and chart a course towards enhanced integration. A major element of this path is the joint orientation towards the continuous refinement of a theoretical framework for FBR that links theory testing and generalization with applied research oriented towards the conservation of biodiversity and ecosystem functioning. We further emphasize existing decision-making frameworks as suitable instruments to practically merge these different aims of FBR and bring them into application. This integrated framework requires joint research planning, and should improve communication and stimulate collaboration between modellers and empiricists, thereby overcoming existing reservations and prejudices. The implementation of this integrative research agenda for FBR requires an adaptation in most national and international funding schemes in order to accommodate such joint teams and their more complex structures and data needs.}, language = {en} } @article{MarquartEldridgeGeissleretal.2020, author = {Marquart, Arnim and Eldridge, David J. and Geissler, Katja and Lobas, Christoph and Blaum, Niels}, title = {Interconnected effects of shrubs, invertebrate-derived macropores and soil texture on water infiltration in a semi-arid savanna rangeland}, series = {Land degradation \& development}, volume = {31}, journal = {Land degradation \& development}, number = {16}, publisher = {Wiley}, address = {Chichester, Sussex}, issn = {1085-3278}, doi = {10.1002/ldr.3598}, pages = {2307 -- 2318}, year = {2020}, abstract = {Many semi arid savannas are prone to degradation, caused for example, by overgrazing or extreme climatic events, which often lead to shrub encroachment. Overgrazing by livestock affects vegetation and infiltration processes by directly altering plant composition (selective grazing) or by impacting soil physical properties (trampling). Water infiltration is controlled by several parameters, such as macropores (created by soil-burrowing animals or plant roots) and soil texture, but their effects have mostly been studied in isolation. Here we report on a study, in which we conducted infiltration experiments to analyze the interconnected effects of invertebrate-created macropores, shrubs and soil texture (sandy soil and loamy sand) on infiltration in two Namibian rangelands. Using structural equation modeling, we found a direct positive effect of shrub size on infiltration and indirectly via invertebrate macropores on both soil types. On loamy sands this effect was even stronger, but additionally, invertebrate-created macropores became relevant as a direct driver of infiltration. Our results provide new insights into the effects of vegetation and invertebrates on infiltration under different soil textures. Pastoralists should use management strategies that maintain a heterogeneous plant community that supports soil fauna to sustain healthy soil water dynamics, particularly on soils with higher loam content. Understanding the fundamental functioning of soil water dynamics in drylands is critical because these ecosystems are water-limited and support the livelihoods of many cultures worldwide.}, language = {en} } @article{SchaldachWimmerKochetal.2013, author = {Schaldach, R{\"u}diger and Wimmer, Florian and Koch, Jennifer and Volland, Jan and Geissler, Katja and K{\"o}chy, Martin}, title = {Model-based analysis of the environmental impacts of grazing management on Eastern Mediterranean ecosystems in Jordan}, series = {Journal of environmental management}, volume = {127}, journal = {Journal of environmental management}, number = {9}, publisher = {Elsevier}, address = {London}, issn = {0301-4797}, doi = {10.1016/j.jenvman.2012.11.024}, pages = {S84 -- S95}, year = {2013}, abstract = {Eastern Mediterranean ecosystems are prone to desertification when under grazing pressure. Therefore, management of grazing intensity plays a crucial role to avoid or to diminish land degradation and to sustain both livelihoods and ecosystem functioning. The dynamic land-use model LandSHIFT was applied to a case study on the country level for Jordan. The impacts of different stocking densities on the environment were assessed through a set of simulation experiments for various combinations of climate input and assumptions about the development of livestock numbers. Indicators used for the analysis include a set of landscape metrics to account for habitat fragmentation and the "Human Appropriation of Net Primary Production" (HANPP), i.e., the difference between the amount of net primary production (NPP) that would be available in a natural ecosystem and the amount of NPP that remains under human management. Additionally, the potential of the economic valuation of ecosystem services, including landscape and grazing services, as an analysis concept was explored. We found that lower management intensities had a positive effect on HANPP but at the same time resulted in a strong increase of grazing area. This effect was even more pronounced under climate change due to a predominantly negative effect on the biomass productivity of grazing land. Also Landscape metrics tend to indicate decreasing habitat fragmentation as a consequence of lower grazing pressure. The valuation of ecosystem services revealed that low grazing intensity can lead to a comparatively higher economic value on the country level average. The results from our study underline the importance of considering grazing management as an important factor to manage dry-land ecosystems in a sustainable manner.}, language = {en} } @article{MuellervanSchaikBlumeetal.2014, author = {M{\"u}ller, Eva Nora and van Schaik, Loes and Blume, Theresa and Bronstert, Axel and Carus, Jana and Fleckenstein, Jan H. and Fohrer, Nicola and Geissler, Katja and Gerke, Horst H. and Gr{\"a}ff, Thomas and Hesse, Cornelia and Hildebrandt, Anke and H{\"o}lker, Franz and Hunke, Philip and K{\"o}rner, Katrin and Lewandowski, J{\"o}rg and Lohmann, Dirk and Meinikmann, Karin and Schibalski, Anett and Schmalz, Britta and Schr{\"o}der-Esselbach, Boris and Tietjen, Britta}, title = {Scales, key aspects, feedbacks and challenges of ecohydrological research in Germany}, series = {Hydrologie und Wasserbewirtschaftung}, volume = {58}, journal = {Hydrologie und Wasserbewirtschaftung}, number = {4}, publisher = {Bundesanst. f{\"u}r Gew{\"a}sserkunde}, address = {Koblenz}, issn = {1439-1783}, doi = {10.5675/HyWa_2014,4_2}, pages = {221 -- 240}, year = {2014}, abstract = {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.}, language = {de} } @article{ReinhardGeisslerBlaum2019, author = {Reinhard, Johanna E. and Geissler, Katja and Blaum, Niels}, title = {Short-term responses of darkling beetles (Coleoptera:Tenebrionidae) to the effects of fire and grazing in savannah rangeland}, series = {Insect Conservation and Diversity}, volume = {12}, journal = {Insect Conservation and Diversity}, number = {1}, publisher = {Wiley}, address = {Hoboken}, issn = {1752-458X}, doi = {10.1111/icad.12324}, pages = {39 -- 48}, year = {2019}, abstract = {Fire and grazing shape biodiversity in savannah landscapes. In land use management, knowing the effects of fire and grazing on biodiversity are important in order to ensure environmental sustainability. Beetles specifically are indicators of the biodiversity response to fire and grazing. A grazing exclusion and burning experiment in a split-plot design was used in order to investigate the interacting effects of fire and wildlife grazing on biomass, diversity, and species composition of darkling beetles (Coleoptera, Tenebrionidae) over time after fire. Darkling beetle species richness and diversity were responding in a three-way-interaction to fire, grazing, and time after fire, whereby biomass of darkling beetles remained unaffected and species compositional changes were attributed to seasonal changes of time only. Fire on ungrazed plots had a negative effect on species diversity and richness 2 weeks and 6 months post fire, whereas fire on grazed plots had no impact on species diversity and richness. Grazing only lowered species diversity and richness 6 months after fire treatments. Results suggest that grazing overrides the effects of fire and that the similar effects caused by fire and grazing are due to niche and assemblage simplification of the habitat.}, language = {en} } @article{HeringHauptfleischGeissleretal.2019, author = {Hering, Robert and Hauptfleisch, Morgan and Geissler, Katja and Marquart, Arnim and Schoenen, Maria and Blaum, Niels}, title = {Shrub encroachment is not always land degradation}, series = {Land degradation \& development}, volume = {30}, journal = {Land degradation \& development}, number = {1}, publisher = {Wiley}, address = {Chichester}, issn = {1085-3278}, doi = {10.1002/ldr.3197}, pages = {14 -- 24}, year = {2019}, abstract = {Shrub encroachment in semi-arid savannas is induced by interacting effects of climate, fire suppression, and unsustainable livestock farming; it carries a severe risk of land degradation and strongly influences natural communities that provide key ecosystem functions. However, species-specific effects of shrub cover on many animal groups that act as indicators of degradation remain largely unknown. We analysed the consequences of shrub encroachment for ground-dwelling beetles in a semi-arid Namibian savanna rangeland, where beetles and vegetation were recorded along a shrub cover gradient (30\%). Focusing on species niche breadths and optima, we identified two crucial shrub cover thresholds (2.9\% and 10.0\%), corresponding to major changes in the beetle communities with implications for savanna ecosystem functioning. Niche optima of most species were between the first and second thresholds; beyond the second threshold, saprophagous, coprophagous, and rare predatory beetles declined in numbers and diversity. This is problematic because beetles provide important ecosystem functions, such as decomposition and nutrient cycling. However, we also found that certain species were adapted to high shrub cover, thus providing examples of niche differentiation. Despite the predominantly negative effects of heavy shrub encroachment on beetle communities, shrubs in their early life stages apparently provide essential structures, which enhance habitat quality for ground-dwelling beetles. Our results demonstrate that shrub encroachment can have mixed effects on ground-dwelling beetle communities and hence on savanna ecosystem functioning. We, therefore, conclude that rangeland management and restoration should consider the complex trade-offs between species-specific effects and the level of encroachment for sustainable land use.}, language = {en} }