TY - JOUR A1 - Jeltsch, Florian A1 - Blaum, Niels A1 - Brose, Ulrich A1 - Chipperfield, Joseph D. A1 - Clough, Yann A1 - Farwig, Nina A1 - Geissler, Katja A1 - Graham, Catherine H. A1 - Grimm, Volker A1 - Hickler, Thomas A1 - Huth, Andreas A1 - May, Felix A1 - Meyer, Katrin M. A1 - Pagel, Jörn A1 - Reineking, Björn A1 - Rillig, Matthias C. A1 - Shea, Katriona A1 - Schurr, Frank Martin A1 - Schroeder, Boris A1 - Tielbörger, Katja A1 - Weiss, Lina A1 - Wiegand, Kerstin A1 - Wiegand, Thorsten A1 - Wirth, Christian A1 - Zurell, Damaris T1 - How can we bring together empiricists and modellers in functional biodiversity research? JF - Basic and applied ecology : Journal of the Gesellschaft für Ökologie N2 - 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. KW - Biodiversity theory KW - Biodiversity experiments KW - Conservation management KW - Decision-making KW - Ecosystem functions and services KW - Forecasting KW - Functional traits KW - Global change KW - Monitoring programmes KW - Interdisciplinarity Y1 - 2013 U6 - https://doi.org/10.1016/j.baae.2013.01.001 SN - 1439-1791 VL - 14 IS - 2 SP - 93 EP - 101 PB - Elsevier CY - Jena ER - TY - JOUR A1 - Geißler, Katja A1 - Mühle, Ralf-Udo A1 - Gzik, Axel T1 - Cnidium dubium und Microtus arvalis : eine Pflanze-Konsument-Interaktion der Unteren Havelaue in Abhängigkeit von der wurzelbürtigen Assimilationsspeicherung Y1 - 2005 ER - TY - THES A1 - Geißler, Katja T1 - Lebensstrategien seltener Stromtalpflanzen : autökologische Untersuchung von Cnidium dubium, Gratiola officinalis und Juncus atratus unter besonderer Berücksichtigung ihrer Stressresistenz T1 - Life strategies of rare river corridor plants : autecological investigation of Cnidium dubium, Gratiola officinalis and Juncus atratus with special consideration of their stress resistance N2 - Die vorliegende Dissertation behandelt die Ökologie von Cnidium dubium (Schkuhr) Thell. (Sumpf-Brenndolde), Gratiola officinalis L. (Gottes-Gnadenkraut) und Juncus atratus Krocker (Schwarze Binse), drei gefährdeten Arten, die als sogenannte Stromtalpflanzen in Mitteleuropa in ihrem Vorkommen eng an die Flussauen gebunden sind. Die Arbeit basiert auf verschiedenen Simulationsexperimenten und Feldstudien in der Unteren Havelniederung, einem „Feuchtgebiet von internationaler Bedeutung“. Sie behandelt Themenkomplexe wie das Samenbankverhalten, die Samenkeimung, die Stickstofflimitierung, die Konkurrenzkraft, das Verhalten der Pflanzen nach einer Sommertrockenheit und nach einer Winter/Frühjahrsüberflutung. Ferner widmet sie sich der Populationsbiologie der Arten und dem Verhalten der Pflanzen nach besonderen Störungsereignissen wie Mahd, Herbivorie und der Sommerflut 2002. Der Leser erfährt, wie die Pflanzen in verschiedenen Lebensphasen auf die auentypische Umwelt reagieren und erhält umfassende Einblicke in physiologische Mechanismen, die der Anpassung an die typischen Bedingungen einer mitteleuropäischen Flussaue dienen. Eine Interpretation der Ergebnisse zeigt auf, welche der spezifischen Eigenschaften zur Gefährdung der drei Stromtalarten beitragen. Die Arbeit ist für den Arten-, Biotop- und Landschaftsschutz interessant. Darüber hinaus bietet sie zahlreiche Anknüpfungspunkte zur ökophysiologischen Grundlagenforschung. Die verstärkte Nutzung physiologischer Methoden bei der Klärung ökologischer Fragestellungen wird angeregt. N2 - The thesis deals with the ecology of three endangered European river corridor angiosperms Cnidium dubium (Schkuhr) Thell., Gratiola officinalis L. und Juncus atratus Krocker. The study is based on different experimental approaches and field surveys in a wetland along the Lower Havel River, a designated German Ramsar-site (Wetland of International Importance). This involves the examination of aspects of seed bank dynamics, germination, nitrogen limitation, competitive ability, and the response of plants to summer drought and/or winter/spring flooding. The thesis continues with a detailed study of the population biology of the species at natural sites and the response of these plants to specific disturbances like mowing, herbivory and the severe summer flooding in 2002. The reader learns about the traits of the three plant species to tolerate the typical conditions their natural sites are exposed to in different phases of their life cycle. He gets a comprehensive look at physiological means by which plants can adapt to the prevailing conditions of European river lowlands. The interpretation of the results is used to reveal specific plant traits, which may contribute to the endangerment of the three river corridor plants. As such, this thesis is interesting for protection of species, biotopes and landscapes. Furthermore, it provides numerous close connections to fundamental research from an ecophysiological perspective. The increased use of physiological methods is recommended in order to be able to adequately resolve ecological problems. KW - untere Havelniederung KW - seltene Pflanzen KW - Stoffwechsel KW - Wachstum KW - Samen KW - Hypoxie KW - Trockenstress KW - Konkurrenz KW - Mahd KW - lower Havel river wetland KW - rare plants KW - metabolism KW - growth KW - seeds KW - hypoxia KW - drought stress KW - competition KW - mowing Y1 - 2008 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus-17468 ER - TY - GEN A1 - Geißler, Katja A1 - Heblack, Jessica A1 - Uugulu, Shoopala A1 - Wanke, Heike A1 - Blaum, Niels T1 - Partitioning of Water Between Differently Sized Shrubs and Potential Groundwater Recharge in a Semiarid Savanna in Namibia T2 - Postprints der Universität Potsdam Mathematisch-Naturwissenschaftliche Reihe N2 - Introduction: Many semiarid regions around the world are presently experiencing significant changes in both climatic conditions and vegetation. This includes a disturbed coexistence between grasses and bushes also known as bush encroachment, and altered precipitation patterns with larger rain events. Fewer, more intense precipitation events might promote groundwater recharge, but depending on the structure of the vegetation also encourage further woody encroachment. Materials and Methods: In this study, we investigated how patterns and sources of water uptake of Acacia mellifera (blackthorn), an important encroaching woody plant in southern African savannas, are associated with the intensity of rain events and the size of individual shrubs. The study was conducted at a commercial cattle farm in the semiarid Kalahari in Namibia (MAP 250 mm/a). We used soil moisture dynamics in different depths and natural stable isotopes as markers of water sources. Xylem water of fifteen differently sized individuals during eight rain events was extracted using a Scholander pressure bomb. Results and Discussion: Results suggest the main rooting activity zone of A. mellifera in 50 and 75 cm soil depth but a reasonable water uptake from 10 and 25 cm. Any apparent uptake pattern seems to be driven by water availability, not time in the season. Bushes prefer the deeper soil layers after heavier rain events, indicating some evidence for the classical Walter’s two-layer hypothesis. However, rain events up to a threshold of 6 mm/day cause shallower depths of use and suggest several phases of intense competition with perennial grasses. The temporal uptake pattern does not depend on shrub size, suggesting a fast upwards water flow inside. d2H and d18O values in xylem water indicate that larger shrubs rely less on upper and very deep soil water than smaller shrubs. It supports the hypothesis that in environments where soil moisture is highly variable in the upper soil layers, the early investment in a deep tap-root to exploit deeper, more reliable water sources could reduce the probability of mortality during the establishment phase. Nevertheless, independent of size and time in the season, bushes do not compete with potential groundwater recharge. In a savanna encroached by A. mellifera, groundwater will most likely be affected indirectly. T3 - Zweitveröffentlichungen der Universität Potsdam : Mathematisch-Naturwissenschaftliche Reihe - 798 KW - bush encroachment KW - groundwater recharge KW - rooting depth KW - Savannas KW - stable isotopes KW - shrub size KW - Acacia mellifera KW - rain event depth Y1 - 2019 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus4-441110 SN - 1866-8372 IS - 798 ER - TY - JOUR A1 - Geißler, Katja A1 - Hahn, Claudia A1 - Joubert, David A1 - Blaum, Niels T1 - Functional responses of the herbaceous plant community explain ecohydrological impacts of savanna shrub encroachment JF - Perspectives in plant ecology, evolution and systematics N2 - Major drivers of savanna shrub encroachment are climatic conditions, CO2 and unsustainable grazing management including fire prevention. Although all drivers affect ecohydrological processes, and given that water is a seasonally scarce resource in savannas, it remains largely unclear how shrub encroachment itself affects hydrological conditions that feed back into water use and community assembly of the remaining plant community. Hence, understanding direct ecohydrological effects of shrubs that may limit the recovery of the perennial herbaceous vegetation in grazed areas and promote the establishment of shrub seedlings facilitates the identification of areas that are most sensitive to further encroachment. In our trait-based approach, we determined relationships among shrub cover, soil and plant trait characteristics sensitive to water limitation in 120 plots along a shrub cover gradient. We focused on two functional response traits indicating immediate drought stress and subsequent water use for drought stress recovery with associated competition for water (midday leaf/xylem water potential and diurnally recovery rate of leaf water potential), and three functional response traits indicating long-term stress adaptation and related resource use strategies (SLA, plant height and seed release height). To understand species assembly and the associated mechanisms of resource use, we calculated community weighted mean traits, intraspecific trait variability as a proxy for the mechanism of coexistence, and mean traits at plant functional type level including 2-year-old Acacia mellifera-saplings. We found a low intraspecific trait variability in drought stress recovery rate and height suggesting that competitive exclusion via active resource acquisition (i.e. water exploitation) played a minor role for community assembly in a shrub encroaching savanna. The dominant community assembly process was passive stress avoidance via resource conservation up to stress tolerance indicated by the high variability in SLA and midday leaf water potential. Correlations of traits with soil moisture suggest a rooting niche differentiation between annual and perennial grasses and that Acacia-shrub saplings within the first 50 cm of soil already escaped the highest drought stress. Interestingly, immediate drought stress for the herbaceous community was lowest on moderately shrub encroached sites and not on grass dominated sites. Since passive stress avoidance accompanied by a distinct stress tolerance in semi-arid savannas is more important than active competition, and assuming that the low drought stress of the herbaceous community at intermediate levels of shrub cover also applies to newly emerging shrub seedlings, these areas are likely to be most sensitive to further encroachment. As such, they should be considered as focal areas for prevention management. KW - Community-weighted means KW - Drought stress KW - Intraspecific variation KW - Soil moisture KW - Stress recovery KW - Plant functional traits Y1 - 2019 U6 - https://doi.org/10.1016/j.ppees.2019.125458 SN - 1433-8319 VL - 39 PB - Elsevier CY - München ER - TY - JOUR A1 - Geissler, Katja A1 - Fiedler, Sebastian A1 - Ni, Jian A1 - Herzschuh, Ulrike A1 - Jeltsch, Florian T1 - Combined effects of grazing and climate warming drive shrub dominance on the Tibetan Plateau JF - The Rangeland journal N2 - 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. KW - alpine grassland degradation KW - herd composition KW - rangeland management KW - shrub encroachment KW - shrubline KW - simulation model Y1 - 2019 U6 - https://doi.org/10.1071/RJ19027 SN - 1036-9872 SN - 1834-7541 VL - 41 IS - 5 SP - 425 EP - 439 PB - CSIRO Publishing CY - Collingwood ER - TY - JOUR A1 - Reinhard, Johanna E. A1 - Geissler, Katja A1 - Blaum, Niels T1 - Short-term responses of darkling beetles (Coleoptera:Tenebrionidae) to the effects of fire and grazing in savannah rangeland JF - Insect Conservation and Diversity N2 - 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. KW - Arid ecosystems KW - arid rangeland KW - beetles KW - herbivory KW - insect diversity KW - land use KW - management Y1 - 2018 U6 - https://doi.org/10.1111/icad.12324 SN - 1752-458X SN - 1752-4598 VL - 12 IS - 1 SP - 39 EP - 48 PB - Wiley CY - Hoboken ER - TY - JOUR A1 - Geissler, Katja A1 - Gzik, Axel T1 - Germination ecology of three endangered river corridor plants in relation to their preferred occurrence N2 - 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. Y1 - 2010 UR - http://www.sciencedirect.com/science/journal/03672530 U6 - https://doi.org/10.1016/j.flora.2010.04.008 SN - 0367-2530 ER - TY - JOUR A1 - Schaldach, Rüdiger A1 - Wimmer, Florian A1 - Koch, Jennifer A1 - Volland, Jan A1 - Geissler, Katja A1 - Köchy, Martin T1 - Model-based analysis of the environmental impacts of grazing management on Eastern Mediterranean ecosystems in Jordan JF - Journal of environmental management N2 - 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. KW - Sustainable management of Mediterranean grazing land KW - Land-use modeling KW - Climate change KW - Landscape metrics KW - Ecosystem service value KW - Human Appropriation of Net Primary Production (HANPP) Y1 - 2013 U6 - https://doi.org/10.1016/j.jenvman.2012.11.024 SN - 0301-4797 SN - 1095-8630 VL - 127 IS - 9 SP - S84 EP - S95 PB - Elsevier CY - London ER - TY - JOUR A1 - Geißler, Katja A1 - Heblack, Jessica A1 - Uugulu, Shoopala A1 - Wanke, Heike A1 - Blaum, Niels T1 - Partitioning of Water Between Differently Sized Shrubs and Potential Groundwater Recharge in a Semiarid Savanna in Namibia JF - Frontiers in Plant Science N2 - Introduction: Many semiarid regions around the world are presently experiencing significant changes in both climatic conditions and vegetation. This includes a disturbed coexistence between grasses and bushes also known as bush encroachment, and altered precipitation patterns with larger rain events. Fewer, more intense precipitation events might promote groundwater recharge, but depending on the structure of the vegetation also encourage further woody encroachment. Materials and Methods: In this study, we investigated how patterns and sources of water uptake of Acacia mellifera (blackthorn), an important encroaching woody plant in southern African savannas, are associated with the intensity of rain events and the size of individual shrubs. The study was conducted at a commercial cattle farm in the semiarid Kalahari in Namibia (MAP 250 mm/a). We used soil moisture dynamics in different depths and natural stable isotopes as markers of water sources. Xylem water of fifteen differently sized individuals during eight rain events was extracted using a Scholander pressure bomb. Results and Discussion: Results suggest the main rooting activity zone of A. mellifera in 50 and 75 cm soil depth but a reasonable water uptake from 10 and 25 cm. Any apparent uptake pattern seems to be driven by water availability, not time in the season. Bushes prefer the deeper soil layers after heavier rain events, indicating some evidence for the classical Walter’s two-layer hypothesis. However, rain events up to a threshold of 6 mm/day cause shallower depths of use and suggest several phases of intense competition with perennial grasses. The temporal uptake pattern does not depend on shrub size, suggesting a fast upwards water flow inside. d2H and d18O values in xylem water indicate that larger shrubs rely less on upper and very deep soil water than smaller shrubs. It supports the hypothesis that in environments where soil moisture is highly variable in the upper soil layers, the early investment in a deep tap-root to exploit deeper, more reliable water sources could reduce the probability of mortality during the establishment phase. Nevertheless, independent of size and time in the season, bushes do not compete with potential groundwater recharge. In a savanna encroached by A. mellifera, groundwater will most likely be affected indirectly. KW - bush encroachment KW - groundwater recharge KW - rooting depth KW - Savannas KW - stable isotopes KW - shrub size KW - Acacia mellifera KW - rain event depth Y1 - 2019 U6 - https://doi.org/10.3389/fpls.2019.01411 SN - 1664-462X VL - 10 PB - Frontiers Media CY - Lausanne ER - TY - JOUR A1 - Hering, Robert A1 - Hauptfleisch, Morgan A1 - Geissler, Katja A1 - Marquart, Arnim A1 - Schoenen, Maria A1 - Blaum, Niels T1 - Shrub encroachment is not always land degradation BT - Insights from ground‐dwelling beetle species niches along a shrub cover gradient in a semi‐arid Namibian savanna JF - Land degradation & development N2 - 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. KW - Coleoptera KW - rangeland KW - semi-arid savanna KW - shrub encroachment KW - species niche KW - threshold Y1 - 2018 U6 - https://doi.org/10.1002/ldr.3197 SN - 1085-3278 SN - 1099-145X VL - 30 IS - 1 SP - 14 EP - 24 PB - Wiley CY - Chichester ER - TY - JOUR A1 - Marquart, Arnim A1 - Eldridge, David J. A1 - Geissler, Katja A1 - Lobas, Christoph A1 - Blaum, Niels T1 - Interconnected effects of shrubs, invertebrate-derived macropores and soil texture on water infiltration in a semi-arid savanna rangeland JF - Land degradation & development N2 - 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. KW - hydrology KW - infiltration KW - invertebrate macropores KW - shrub-encroachment KW - soil function KW - soil texture Y1 - 2020 U6 - https://doi.org/10.1002/ldr.3598 SN - 1085-3278 SN - 1099-145X VL - 31 IS - 16 SP - 2307 EP - 2318 PB - Wiley CY - Chichester, Sussex ER - TY - JOUR A1 - Reinhard, Johanna E. A1 - Geißler, Katja A1 - Blaum, Niels T1 - Grass and ground dwelling beetle community responses to holistic and wildlife grazing management using a cross-fence comparison in Western Kalahari rangeland, Namibia JF - Journal of insect conservation : an international journal devoted to the conservation of insects and related invertebrates N2 - Savannahs are often branded by livestock grazing with resulting land degradation. Holistic management of livestock was proposed to contribute to biodiversity conservation by simulating native wildlife grazing behaviour. This study attempts the comparison of the impact of a holistic management regime to a wildlife grazing management regime on grass and ground-dwelling beetle species diversity on neighboring farms in Namibian rangeland. Results show that the response of biodiversity in species richness and composition to holistic management of livestock differs substantially from wildlife grazing with a positive impact. From a total of 39 identified species of ground-dwelling beetles (Coleoptera: Tenebrionidae, Carabidae) from 29 genera, eight species were found to be indicators for holistic management of livestock and three were found to be indicators for wildlife grazed rangeland. Observations suggest that holistic management of livestock may contribute to biodiversity conservation, but the differential effect of grazing management on species assemblages suggests that livestock grazing cannot replace native wildlife herbivory. Implications for insect conservation An adaptive management strategy such as holistic management used in this study shows the potential to support high beetle biodiversity. Holistic management of livestock thus aspects in favour for a sustainable form of grazing management for insect conservation even though it does not functionally replace grazing by native wildlife. KW - Beetle conservation KW - Land use management KW - Biodiversity KW - Insect conservation KW - Wildlife management Y1 - 2022 U6 - https://doi.org/10.1007/s10841-022-00410-6 SN - 1366-638X SN - 1572-9753 VL - 26 SP - 711 EP - 720 PB - Springer CY - Dordrecht ER - TY - JOUR A1 - Bergholz, Kolja A1 - Jeltsch, Florian A1 - Weiß, Lina A1 - Pottek, Janine A1 - Geißler, Katja A1 - Ristow, Michael T1 - Fertilization affects the establishment ability of species differing in seed mass via direct nutrient addition and indirect competition effects JF - Oikos N2 - Fertilization causes species loss and species dominance changes in plant communities worldwide. However, it still remains unclear how fertilization acts upon species functional traits, e.g. seed mass. Seed mass is a key trait of the regeneration strategy of plants, which influences a range of processes during the seedling establishment phase. Fertilization may select upon seed mass, either directly by increased nutrient availability or indirectly by increased competition. Since previous research has mainly analyzed the indirect effects of fertilization, we disentangled the direct and indirect effects to examine how nutrient availability and competition influence the seed mass relationships on four key components during seedling establishment: seedling emergence, time of seedling emergence, seedling survival and seedling growth. We conducted a common garden experiment with 22 dry grassland species with a two-way full factorial design that simulated additional nutrient supply and increased competition. While we found no evidence that fertilization either directly by additional nutrient supply or indirectly by increased competition alters the relationship between seed mass and (time of) seedling emergence, we revealed that large seed mass is beneficial under nutrient-poor conditions (seedlings have greater chances of survival, particularly in nutrient-poor soils) as well as under competition (large-seeded species produced larger seedlings, which suffered less from competition than small-seeded species). Based on these findings, we argue that both factors, i.e. nutrient availability and competition intensity, ought to be considered to understand how fertilization influences seedling establishment and species composition with respect to seed mass in natural communities. We propose a simple conceptual model, in which seed mass in natural communities is determined by competition intensity and nutrient availability. Here, we hypothesize that seed mass shows a U-shaped pattern along gradients of soil fertility, which may explain the contrasting soil fertility-seed mass relationships found in the recent literature. Y1 - 2015 U6 - https://doi.org/10.1111/oik.02193 SN - 0030-1299 SN - 1600-0706 VL - 124 IS - 11 SP - 1547 EP - 1554 PB - Wiley-Blackwell CY - Hoboken ER - TY - JOUR A1 - Weiss, Lina A1 - Schalow, Linda A1 - Jeltsch, Florian A1 - Geissler, Katja T1 - Experimental evidence for root competition effects on community evenness in one of two phytometer species JF - Journal of plant ecology N2 - 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. KW - plant-plant interactions KW - root and shoot competition KW - intensity vs KW - importance KW - experimental plant communities KW - asymmetry of competition Y1 - 2018 U6 - https://doi.org/10.1093/jpe/rty021 SN - 1752-9921 SN - 1752-993X VL - 12 IS - 2 SP - 281 EP - 291 PB - Oxford Univ. Press CY - Oxford ER - TY - JOUR A1 - Lohmann, Dirk A1 - Falk, Thomas A1 - Geissler, Katja A1 - Blaum, Niels A1 - Jeltsch, Florian T1 - Determinants of semi-arid rangeland management in a land reform setting in Namibia JF - Journal of arid environments N2 - 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. KW - Dry land degradation KW - Semi-arid savanna KW - Land reform KW - Rangeland management KW - Simulation model KW - Role-play Y1 - 2014 U6 - https://doi.org/10.1016/j.jaridenv.2013.10.005 SN - 0140-1963 SN - 1095-922X VL - 100 SP - 23 EP - 30 PB - Elsevier CY - London ER - TY - GEN A1 - Synodinos, Alexios D. A1 - Eldridge, David A1 - Geißler, Katja A1 - Jeltsch, Florian A1 - Lohmann, Dirk A1 - Midgley, Guy A1 - Blaum, Niels T1 - Remotely sensed canopy height reveals three pantropical ecosystem states BT - a comment T2 - Ecology : a publication of the Ecological Society of America Y1 - 2017 U6 - https://doi.org/10.1002/ecy.1997 SN - 0012-9658 SN - 1939-9170 VL - 99 IS - 1 SP - 231 EP - 234 PB - Wiley CY - Hoboken 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 -