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 - 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 - 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 - 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 - 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 - 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 - 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 -